   PBO issue using SDL
  Currently I am using SDL for my openGL application which using Pixel Buffer Object (PBO) to capture screen pixels, an advanced buffer technique. The issue that I am facing currently is that after binding to the pbo, the pixels read time is much more than expected approx. 11ms. But if run the same application using GLUT library instead of PBO or using some plain windows programming in which the screen built using WinMain then it gives much faster read time of approx. 0.01 ms. The only difference between all these three applications is that the windows are built using different techniques. But all other code is exactly similar. I am also pasting my code here for review for all of the three different techniques.1. First code is using SDL (Read time is 11ms)   ===========================================/* *  SimpleSDL.cpp *  SimpleSDL * *  Created by david on 19/06/2010. */// in order to get function prototypes from glext.h, define GL_GLEXT_PROTOTYPES before including glext.h#define GL_GLEXT_PROTOTYPES#define SCREEN_WIDTH256//800#define SCREEN_HEIGHT256//600#define SCREEN_BPP32#include <iostream>#include <vector>#ifdef __APPLE__//Apple Headers//#include <OpenGL/OpenGL.h>#include <GLUT/glut.h>#include "SDL.h"#include "SDL_opengl.h"#else//Windows and linux headers#include "oglext\glext.h"#include "SDL.h"#include "SDL_opengl.h"#include <gl\gl.h>#include <gl\glu.h>#include "glut.h"#include <iostream>#include <sstream>#include <iomanip>#include "Timer.h"#include "glInfo.h"    // glInfo struct#endifusing std::stringstream;using std::cout;using std::endl;using std::ends;// VBO Extension Definitions, From glext.h#define GL_ARRAY_BUFFER_ARB 0x8892#define GL_STATIC_DRAW_ARB 0x88E4typedef void (APIENTRY * PFNGLBINDBUFFERARBPROC) (GLenum target, GLuint buffer);typedef void (APIENTRY * PFNGLDELETEBUFFERSARBPROC) (GLsizei n, const GLuint *buffers);typedef void (APIENTRY * PFNGLGENBUFFERSARBPROC) (GLsizei n, GLuint *buffers);typedef void (APIENTRY * PFNGLBUFFERDATAARBPROC) (GLenum target, int size, const GLvoid *data, GLenum usage);typedef void (APIENTRY * PFNGLBUFFERSUBDATAARBPROC) (GLenum, GLintptrARB, GLsizeiptrARB, GLvoid const *);typedef void (APIENTRY * PFNGLGETBUFFERPARAMETERIVARBPROC) (GLenum, GLenum, GLint *);typedef GLvoid* (APIENTRY * PFNGLMAPBUFFERARBPROC) (GLenum, GLenum);typedef GLboolean* (APIENTRY * PFNGLUNMAPBUFFERARBPROC) (GLenum);//Surface for OpenGL to be drawn toSDL_Surface *screen = NULL;//False unti program quit by ESC or clicking top corner 'X'bool quit;//Keyboard and other Input Device eventsSDL_Event event;GLfloatrtri;// Angle For The Triangle ( NEW )GLfloatrquad;// Angle For The Quad ( NEW )// function pointers for PBO Extension// Windows needs to get function pointers from ICD OpenGL drivers,// because opengl32.dll does not support extensions higher than v1.1.#ifdef _WIN32PFNGLGENBUFFERSARBPROC pglGenBuffersARB = 0; // VBO Name Generation ProcedurePFNGLBINDBUFFERARBPROC pglBindBufferARB = 0; // VBO Bind ProcedurePFNGLBUFFERDATAARBPROC pglBufferDataARB = 0; // VBO Data Loading ProcedurePFNGLBUFFERSUBDATAARBPROC pglBufferSubDataARB = 0;// VBO Sub Data Loading ProcedurePFNGLDELETEBUFFERSARBPROC pglDeleteBuffersARB = 0;// VBO Deletion ProcedurePFNGLGETBUFFERPARAMETERIVARBPROC pglGetBufferParameterivARB = 0; // return various parameters of VBOPFNGLMAPBUFFERARBPROC pglMapBufferARB = 0;   // map VBO procedurePFNGLUNMAPBUFFERARBPROC pglUnmapBufferARB = 0;    // unmap VBO procedure#define glGenBuffersARB pglGenBuffersARB#define glBindBufferARB pglBindBufferARB#define glBufferDataARB pglBufferDataARB#define glBufferSubDataARB   pglBufferSubDataARB#define glDeleteBuffersARB   pglDeleteBuffersARB#define glGetBufferParameterivARB pglGetBufferParameterivARB#define glMapBufferARB  pglMapBufferARB#define glUnmapBufferARBpglUnmapBufferARB#endif// constants//const int SCREEN_WIDTH = 256;//const int SCREEN_HEIGHT = 256;const int CHANNEL_COUNT = 4;const int DATA_SIZE = SCREEN_WIDTH * SCREEN_HEIGHT * CHANNEL_COUNT;const GLenum PIXEL_FORMAT = GL_BGRA;const int PBO_COUNT = 2;// global variablesvoid *font = GLUT_BITMAP_8_BY_13;bool pboSupported;GLubyte* colorBuffer = 0;bool pboUsed;GLuint pboIds[PBO_COUNT]; // IDs of PBOsfloat cameraAngleX;float cameraAngleY;float cameraDistance;Timer timer, t1;float readTime, processTime;//Methods In Programbool init();void init_GL();bool init_SDL();void clean_up();void display();void draw();void handle_input();///////////////////////////////////////////////////////////////////////////////// change the brightness///////////////////////////////////////////////////////////////////////////////void add(unsigned char* src, int width, int height, int shift, unsigned char* dst){    if(!src || !dst)   return;    int value;    for(int i = 0; i < height; ++i)    {   for(int j = 0; j < width; ++j)   {  value = *src + shift;  if(value > 255) *dst = (unsigned char)255;  else  *dst = (unsigned char)value;  ++src;  ++dst;  value = *src + shift;  if(value > 255) *dst = (unsigned char)255;  else  *dst = (unsigned char)value;  ++src;  ++dst;  value = *src + shift;  if(value > 255) *dst = (unsigned char)255;  else  *dst = (unsigned char)value;  ++src;  ++dst;  ++src;    // skip alpha  ++dst;   }    }}void toOrtho(){    // set viewport to be the entire window    glViewport((GLsizei)SCREEN_WIDTH, 0, (GLsizei)SCREEN_WIDTH, (GLsizei)SCREEN_HEIGHT);    // set orthographic viewing frustum    glMatrixMode(GL_PROJECTION);    glLoadIdentity();    glOrtho(0, SCREEN_WIDTH, 0, SCREEN_HEIGHT, -1, 1);    // switch to modelview matrix in order to set scene    glMatrixMode(GL_MODELVIEW);    glLoadIdentity();    gluLookAt(0, 0, 0, 0, 0, -1, 0, 1, 0); // eye(x,y,z), focal(x,y,z), up(x,y,z)}void toPerspective(){    // set viewport to be the entire window    glViewport(0, 0, (GLsizei)SCREEN_WIDTH, (GLsizei)SCREEN_HEIGHT);    // set perspective viewing frustum    glMatrixMode(GL_PROJECTION);    glLoadIdentity();    gluPerspective(60.0f, (float)(SCREEN_WIDTH)/SCREEN_HEIGHT, 1.0f, 1000.0f); // FOV, AspectRatio, NearClip, FarClip    // switch to modelview matrix in order to set scene    glMatrixMode(GL_MODELVIEW);    glLoadIdentity();    gluLookAt(0, 0, 8, 0, 0, 0, 0, 1, 0); // eye(x,y,z), focal(x,y,z), up(x,y,z)}///////////////////////////////////////////////////////////////////////////////// write 2d text using GLUT// The projection matrix must be set to orthogonal before call this function.///////////////////////////////////////////////////////////////////////////////void drawString(const char *str, int x, int y, float color[4], void *font){    glPushAttrib(GL_LIGHTING_BIT | GL_CURRENT_BIT); // lighting and color mask    glDisable(GL_LIGHTING);// need to disable lighting for proper text color    glDisable(GL_TEXTURE_2D);    glColor4fv(color);// set text color    glRasterPos2i(x, y);   // place text position    // loop all characters in the string    while(*str)    {   glutBitmapCharacter(font, *str);   ++str;    }    glEnable(GL_TEXTURE_2D);    glEnable(GL_LIGHTING);    glPopAttrib();}///////////////////////////////////////////////////////////////////////////////// display info messages///////////////////////////////////////////////////////////////////////////////void showInfo(){    // backup current model-view matrix    glPushMatrix(); // save current modelview matrix    glLoadIdentity();    // reset modelview matrix    // set to 2D orthogonal projection    glMatrixMode(GL_PROJECTION);// switch to projection matrix    glPushMatrix();   // save current projection matrix    glLoadIdentity(); // reset projection matrix    gluOrtho2D(0, SCREEN_WIDTH, 0, SCREEN_HEIGHT);  // set to orthogonal projection    const int FONT_HEIGHT = 14;    float color[4] = {1, 1, 1, 1};    stringstream ss;    ss << "PBO: ";    if(pboUsed)   ss << "on" << ends;    else   ss << "off" << ends;    drawString(ss.str().c_str(), 1, SCREEN_HEIGHT-FONT_HEIGHT, color, font);    ss.str(""); // clear buffer    ss << "Read Time: " << readTime << " ms" << ends;    drawString(ss.str().c_str(), 1, SCREEN_HEIGHT-(2*FONT_HEIGHT), color, font);    ss.str("");    ss << std::fixed << std::setprecision(3);    ss << "Process Time: " << processTime << " ms" << ends;    drawString(ss.str().c_str(), 1, SCREEN_HEIGHT-(3*FONT_HEIGHT), color, font);    ss.str("");    ss << "Press SPACE to toggle PBO." << ends;    drawString(ss.str().c_str(), 1, 1, color, font);    // unset floating format    ss << std::resetiosflags(std::ios_base::fixed | std::ios_base::floatfield);    // restore projection matrix    glPopMatrix();    // restore to previous projection matrix    // restore modelview matrix    glMatrixMode(GL_MODELVIEW); // switch to modelview matrix    glPopMatrix();    // restore to previous modelview matrix}///////////////////////////////////////////////////////////////////////////////// display transfer rates///////////////////////////////////////////////////////////////////////////////void showTransferRate(){    static Timer timer;    static int count = 0;    static stringstream ss;    double elapsedTime;    // backup current model-view matrix    glPushMatrix(); // save current modelview matrix    glLoadIdentity();    // reset modelview matrix    // set to 2D orthogonal projection    glMatrixMode(GL_PROJECTION);   // switch to projection matrix    glPushMatrix(); // save current projection matrix    glLoadIdentity();    // reset projection matrix    gluOrtho2D(0, SCREEN_WIDTH, 0, SCREEN_HEIGHT); // set to orthogonal projection    float color[4] = {1, 1, 0, 1};    // update fps every second    elapsedTime = timer.getElapsedTime();    if(elapsedTime < 1.0)    {   ++count;    }    else    {   ss.str("");   ss << std::fixed << std::setprecision(1);   ss << "Transfer Rate: " << (count / elapsedTime) * (SCREEN_WIDTH * SCREEN_HEIGHT) / (1024 * 1024) << " Mp" << ends; // update fps string   ss << std::resetiosflags(std::ios_base::fixed | std::ios_base::floatfield);   count = 0;  // reset counter   timer.start();   // restart timer    }    drawString(ss.str().c_str(), 200, 286, color, font);    // restore projection matrix    glPopMatrix();  // restore to previous projection matrix    // restore modelview matrix    glMatrixMode(GL_MODELVIEW);    // switch to modelview matrix    glPopMatrix();  // restore to previous modelview matrix}///////////////////////////////////////////////////////////////////////////////// print transfer rates///////////////////////////////////////////////////////////////////////////////void printTransferRate(){    const double INV_MEGA = 1.0 / (1024 * 1024);    static Timer timer;    static int count = 0;    static stringstream ss;    double elapsedTime;    // loop until 1 sec passed    elapsedTime = timer.getElapsedTime();    if(elapsedTime < 1.0)    {   ++count;    }    else    {   cout << std::fixed << std::setprecision(1);   cout << "Transfer Rate: " << (count / elapsedTime) * (SCREEN_WIDTH * SCREEN_HEIGHT) * INV_MEGA << " Mpixels/s. (" << count / elapsedTime << " FPS)\n";   cout << std::resetiosflags(std::ios_base::fixed | std::ios_base::floatfield);   count = 0;  // reset counter   timer.start();   // restart timer    }}int DrawLesson5Scene(GLvoid)// Here's Where We Do All The Drawing{//glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);// Clear Screen And Depth Buffer//glLoadIdentity();// Reset The Current Modelview MatrixglTranslatef(-1.5f,0.0f,-6.0f);// Move Left 1.5 Units And Into The Screen 6.0glRotatef(rtri,0.0f,1.0f,0.0f);// Rotate The Triangle On The Y axis ( NEW )glBegin(GL_TRIANGLES);// Start Drawing A TriangleglColor3f(1.0f,0.0f,0.0f);// RedglVertex3f( 0.0f, 1.0f, 0.0f);// Top Of Triangle (Front)glColor3f(0.0f,1.0f,0.0f);// GreenglVertex3f(-1.0f,-1.0f, 1.0f);// Left Of Triangle (Front)glColor3f(0.0f,0.0f,1.0f);// BlueglVertex3f( 1.0f,-1.0f, 1.0f);// Right Of Triangle (Front)glColor3f(1.0f,0.0f,0.0f);// RedglVertex3f( 0.0f, 1.0f, 0.0f);// Top Of Triangle (Right)glColor3f(0.0f,0.0f,1.0f);// BlueglVertex3f( 1.0f,-1.0f, 1.0f);// Left Of Triangle (Right)glColor3f(0.0f,1.0f,0.0f);// GreenglVertex3f( 1.0f,-1.0f, -1.0f);// Right Of Triangle (Right)glColor3f(1.0f,0.0f,0.0f);// RedglVertex3f( 0.0f, 1.0f, 0.0f);// Top Of Triangle (Back)glColor3f(0.0f,1.0f,0.0f);// GreenglVertex3f( 1.0f,-1.0f, -1.0f);// Left Of Triangle (Back)glColor3f(0.0f,0.0f,1.0f);// BlueglVertex3f(-1.0f,-1.0f, -1.0f);// Right Of Triangle (Back)glColor3f(1.0f,0.0f,0.0f);// RedglVertex3f( 0.0f, 1.0f, 0.0f);// Top Of Triangle (Left)glColor3f(0.0f,0.0f,1.0f);// BlueglVertex3f(-1.0f,-1.0f,-1.0f);// Left Of Triangle (Left)glColor3f(0.0f,1.0f,0.0f);// GreenglVertex3f(-1.0f,-1.0f, 1.0f);// Right Of Triangle (Left)glEnd();// Done Drawing The PyramidglLoadIdentity();// Reset The Current Modelview MatrixglTranslatef(1.5f,0.0f,-7.0f);// Move Right 1.5 Units And Into The Screen 7.0glRotatef(rquad,1.0f,1.0f,1.0f);// Rotate The Quad On The X axis ( NEW )glBegin(GL_QUADS);// Draw A QuadglColor3f(0.0f,1.0f,0.0f);// Set The Color To BlueglVertex3f( 1.0f, 1.0f,-1.0f);// Top Right Of The Quad (Top)glVertex3f(-1.0f, 1.0f,-1.0f);// Top Left Of The Quad (Top)glVertex3f(-1.0f, 1.0f, 1.0f);// Bottom Left Of The Quad (Top)glVertex3f( 1.0f, 1.0f, 1.0f);// Bottom Right Of The Quad (Top)glColor3f(1.0f,0.5f,0.0f);// Set The Color To OrangeglVertex3f( 1.0f,-1.0f, 1.0f);// Top Right Of The Quad (Bottom)glVertex3f(-1.0f,-1.0f, 1.0f);// Top Left Of The Quad (Bottom)glVertex3f(-1.0f,-1.0f,-1.0f);// Bottom Left Of The Quad (Bottom)glVertex3f( 1.0f,-1.0f,-1.0f);// Bottom Right Of The Quad (Bottom)glColor3f(1.0f,0.0f,0.0f);// Set The Color To RedglVertex3f( 1.0f, 1.0f, 1.0f);// Top Right Of The Quad (Front)glVertex3f(-1.0f, 1.0f, 1.0f);// Top Left Of The Quad (Front)glVertex3f(-1.0f,-1.0f, 1.0f);// Bottom Left Of The Quad (Front)glVertex3f( 1.0f,-1.0f, 1.0f);// Bottom Right Of The Quad (Front)glColor3f(1.0f,1.0f,0.0f);// Set The Color To YellowglVertex3f( 1.0f,-1.0f,-1.0f);// Top Right Of The Quad (Back)glVertex3f(-1.0f,-1.0f,-1.0f);// Top Left Of The Quad (Back)glVertex3f(-1.0f, 1.0f,-1.0f);// Bottom Left Of The Quad (Back)glVertex3f( 1.0f, 1.0f,-1.0f);// Bottom Right Of The Quad (Back)glColor3f(0.0f,0.0f,1.0f);// Set The Color To BlueglVertex3f(-1.0f, 1.0f, 1.0f);// Top Right Of The Quad (Left)glVertex3f(-1.0f, 1.0f,-1.0f);// Top Left Of The Quad (Left)glVertex3f(-1.0f,-1.0f,-1.0f);// Bottom Left Of The Quad (Left)glVertex3f(-1.0f,-1.0f, 1.0f);// Bottom Right Of The Quad (Left)glColor3f(1.0f,0.0f,1.0f);// Set The Color To VioletglVertex3f( 1.0f, 1.0f,-1.0f);// Top Right Of The Quad (Right)glVertex3f( 1.0f, 1.0f, 1.0f);// Top Left Of The Quad (Right)glVertex3f( 1.0f,-1.0f, 1.0f);// Bottom Left Of The Quad (Right)glVertex3f( 1.0f,-1.0f,-1.0f);// Bottom Right Of The Quad (Right)glEnd();// Done Drawing The Quadrtri+=0.2f;// Increase The Rotation Variable For The Triangle ( NEW )rquad-=0.15f;// Decrease The Rotation Variable For The Quad ( NEW )return TRUE;// Keep Going}int DrawGLScene(GLvoid)// Here's Where We Do All The Drawing{static int shift = 0;    static int index = 0;    int nextIndex = 0;   // pbo index used for next frame    // brightness shift amount    shift = ++shift % 200;    // increment current index first then get the next index    // "index" is used to read pixels from a framebuffer to a PBO    // "nextIndex" is used to process pixels in the other PBO    index = (index + 1) % 2;    nextIndex = (index + 1) % 2;// set the framebuffer to read    glReadBuffer(GL_FRONT);GLuint* srcTex;    if(pboUsed) // with PBO    {   // read framebuffer ///////////////////////////////    timer.start();    // copy pixels from framebuffer to PBO   // Use offset instead of ponter.   // OpenGL should perform asynch DMA transfer, so glReadPixels() will return immediately.   glBindBufferARB(GL_PIXEL_PACK_BUFFER_ARB, pboIds[index]);glReadPixels(0, 0, SCREEN_WIDTH, SCREEN_HEIGHT, PIXEL_FORMAT, GL_UNSIGNED_BYTE, 0);// measure the time reading framebuffer   timer.stop();   readTime = timer.getElapsedTimeInMilliSec();   ///////////////////////////////////////////////////   // process pixel data /////////////////////////////   // map the PBO that contain framebuffer pixels before processing it   glBindBufferARB(GL_PIXEL_PACK_BUFFER_ARB, pboIds[nextIndex]);   GLubyte* src = (GLubyte*) glMapBufferARB(GL_PIXEL_PACK_BUFFER_ARB, GL_READ_ONLY_ARB);   if(src)   {  // change brightness  add(src, SCREEN_WIDTH, SCREEN_HEIGHT, shift, colorBuffer);  glUnmapBufferARB(GL_PIXEL_PACK_BUFFER_ARB);// release pointer to the mapped buffer   }    glBindBufferARB(GL_PIXEL_PACK_BUFFER_ARB, 0);    } else   // without PBO    { // read framebuffer ///////////////////////////////   timer.start();   // read framebuffer ///////////////////////////////  glReadPixels(0, 0, SCREEN_WIDTH, SCREEN_HEIGHT, PIXEL_FORMAT, GL_UNSIGNED_BYTE, colorBuffer);   // measure the time reading framebuffer   timer.stop();   readTime = timer.getElapsedTimeInMilliSec();   ///////////////////////////////////////////////////    // change brightness   add(colorBuffer, SCREEN_WIDTH, SCREEN_HEIGHT, shift, colorBuffer);    }  // render to the framebuffer //////////////////////////glDrawBuffer(GL_BACK); toPerspective(); // set to perspective on the left side of the window // clear buffer    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);    ////// tramsform camera    //glTranslatef(0, 0, cameraDistance);    //glRotatef(cameraAngleX, 1, 0, 0);   // pitch    //glRotatef(cameraAngleY, 0, 1, 0);   // heading    //// draw a cube    //draw();DrawLesson5Scene();    // draw the read color buffer to the right side of the window    toOrtho(); // set to orthographic on the right side of the window    glRasterPos2i(0, 0);glDrawPixels(SCREEN_WIDTH, SCREEN_HEIGHT, PIXEL_FORMAT, GL_UNSIGNED_BYTE, colorBuffer);showInfo();printTransferRate();//glutSwapBuffers();return TRUE;// Keep Going}/*-------------------------------------------------- * Setup SDL *--------------------------------------------------*/bool init_SDL(){//Init all SDL Partsif(SDL_Init(SDL_INIT_EVERYTHING) == -1){return false;} //screen = SDL_SetVideoMode( SCREEN_WIDTH, SCREEN_HEIGHT, SCREEN_BPP, SDL_OPENGL | SDL_DOUBLEBUF | SDL_FULLSCREEN );//FULLSCREENscreen = SDL_SetVideoMode( SCREEN_WIDTH*2, SCREEN_HEIGHT, SCREEN_BPP, SDL_OPENGL | SDL_DOUBLEBUF);SDL_WM_SetCaption("Simple SDL Demo", NULL);  return true;}/*-------------------------------------------------- * Init OpenGL *--------------------------------------------------*/void init_GL(){// get OpenGL info    glInfo glInfo;    glInfo.getInfo();    glInfo.printSelf();#ifdef _WIN32    // check PBO is supported by your video card    if(glInfo.isExtensionSupported("GL_ARB_pixel_buffer_object"))    {   // get pointers to GL functions   glGenBuffersARB = (PFNGLGENBUFFERSARBPROC)wglGetProcAddress("glGenBuffersARB");   glBindBufferARB = (PFNGLBINDBUFFERARBPROC)wglGetProcAddress("glBindBufferARB");   glBufferDataARB = (PFNGLBUFFERDATAARBPROC)wglGetProcAddress("glBufferDataARB");   glBufferSubDataARB = (PFNGLBUFFERSUBDATAARBPROC)wglGetProcAddress("glBufferSubDataARB");   glDeleteBuffersARB = (PFNGLDELETEBUFFERSARBPROC)wglGetProcAddress("glDeleteBuffersARB");   glGetBufferParameterivARB = (PFNGLGETBUFFERPARAMETERIVARBPROC)wglGetProcAddress("glGetBufferParameterivARB");   glMapBufferARB = (PFNGLMAPBUFFERARBPROC)wglGetProcAddress("glMapBufferARB");   glUnmapBufferARB = (PFNGLUNMAPBUFFERARBPROC)wglGetProcAddress("glUnmapBufferARB");   // check once again PBO extension   if(glGenBuffersARB && glBindBufferARB && glBufferDataARB && glBufferSubDataARB && glMapBufferARB && glUnmapBufferARB && glDeleteBuffersARB && glGetBufferParameterivARB)   {  pboSupported = pboUsed = true;  //cout << "Video card supports GL_ARB_pixel_buffer_object." << endl;   }   else   {  pboSupported = pboUsed = false; // cout << "Video card does NOT support GL_ARB_pixel_buffer_object." << endl;   }    }#else // for linux, do not need to get function pointers, it is up-to-date    if(glInfo.isExtensionSupported("GL_ARB_pixel_buffer_object"))    {   pboSupported = pboUsed = true;   cout << "Video card supports GL_ARB_pixel_buffer_object." << endl;    }    else    {   pboSupported = pboUsed = false;   cout << "Video card does NOT support GL_ARB_pixel_buffer_object." << endl;    }#endifif(pboSupported)    {   // create 2 pixel buffer objects, you need to delete them when program exits.   // glBufferDataARB with NULL pointer reserves only memory space.   glGenBuffersARB(PBO_COUNT, pboIds);   glBindBufferARB(GL_PIXEL_PACK_BUFFER_ARB, pboIds[0]);   glBufferDataARB(GL_PIXEL_PACK_BUFFER_ARB, DATA_SIZE, 0, GL_STREAM_READ_ARB);   glBindBufferARB(GL_PIXEL_PACK_BUFFER_ARB, pboIds[1]);   glBufferDataARB(GL_PIXEL_PACK_BUFFER_ARB, DATA_SIZE, 0, GL_STREAM_READ_ARB);   glBindBufferARB(GL_PIXEL_PACK_BUFFER_ARB, 0);    }glShadeModel(GL_SMOOTH);// Enable Smooth ShadingglClearColor(0.0f, 0.0f, 0.0f, 0.5f);// Black BackgroundglClearDepth(1.0f);// Depth Buffer SetupglEnable(GL_DEPTH_TEST);// Enables Depth TestingglDepthFunc(GL_LEQUAL);// The Type Of Depth Testing To DoglHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST);// Really Nice Perspective Calculations//glClearColor(0.8, 0.7, 0.9, 1.0);glViewport(0, 0, SCREEN_WIDTH, SCREEN_HEIGHT);}/*-------------------------------------------------- * Init Everything *--------------------------------------------------*/bool init(){// allocate buffers to store frames    colorBuffer = new GLubyte[DATA_SIZE];    memset(colorBuffer, 255, DATA_SIZE);if(init_SDL() == false){std::cout << "Setting Up SDL Failed - Now Exiting or Crashing" << std::endl;return false;}elsestd::cout<< "SDL Initialized " << std::endl; init_GL();std::cout << "OpenGL Initialized" << std::endl; quit = false; return true;}/*----------------------------------------------------------------- *Clean Up RAM Before Quitting *----------------------------------------------------------------- */void clean_up(){// deallocate frame buffer    delete [] colorBuffer;    colorBuffer = 0;// clean up PBOs    if(pboSupported)    {   glDeleteBuffersARB(PBO_COUNT, pboIds);    }//Close All SDL SubsystemsSDL_Quit();}/*-------------------------------------------------- *Draw Scene Code *--------------------------------------------------*/void draw(){glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); glMatrixMode(GL_PROJECTION);glLoadIdentity();gluPerspective(43.0, SCREEN_WIDTH/SCREEN_HEIGHT, 1, 50);glMatrixMode(GL_MODELVIEW);glLoadIdentity();//DRAW CODE HERESDL_GL_SwapBuffers();}/*-------------------------------------------------- * Handle input Code *--------------------------------------------------*/void handle_input(){if(SDL_PollEvent(&event)){switch(event.type){case SDL_KEYDOWN:switch(event.key.keysym.sym){//ESCAPEcase SDLK_ESCAPE:quit = true;break;//SPACEdefault:break;}break;//EXIT SYSTEMcase SDL_QUIT:quit = true;break;}}}/*----------------------------------------------------------------- *Main Method *----------------------------------------------------------------- */int main(int argc, char *args[]){if(init() == false){std::cout << "Problem Initialising" << std::endl;return 1;}  do{//GAME MAIN LOOP GOES HERE handle_input();//draw();DrawGLScene();SDL_GL_SwapBuffers(); }while(!quit); clean_up();return 0;  }================================================================================================================================================================2.    Second technique is using GLUT Library (Read time: 0.01ms approx.) ===================================================================///////////////////////////////////////////////////////////////////////////////// main.cpp// ========// testing Pixel Buffer Object for packing (read-back) pixel data from// framebuffer to a PBO using GL_ARB_pixel_buffer_object extension////  AUTHOR: Song Ho Ahn (song.ahn@gmail.com)// CREATED: 2007-11-30// UPDATED: 2008-06-12///////////////////////////////////////////////////////////////////////////////// in order to get function prototypes from glext.h, define GL_GLEXT_PROTOTYPES before including glext.h#define GL_GLEXT_PROTOTYPES#include <cstdlib>#ifdef __APPLE__#include <GLUT/glut.h>#else#include "glut.h"#endif#include "glext.h"#include <iostream>#include <sstream>#include <iomanip>#include "glInfo.h"    // glInfo struct#include "Timer.h"using std::stringstream;using std::cout;using std::endl;using std::ends;// GLUT CALLBACK functionsvoid displayCB();void reshapeCB(int w, int h);void timerCB(int millisec);void idleCB();void keyboardCB(unsigned char key, int x, int y);void mouseCB(int button, int stat, int x, int y);void mouseMotionCB(int x, int y);void initGL();int  initGLUT(int argc, char **argv);bool initSharedMem();void clearSharedMem();void initLights();void setCamera(float posX, float posY, float posZ, float targetX, float targetY, float targetZ);void drawString(const char *str, int x, int y, float color[4], void *font);void drawString3D(const char *str, float pos[3], float color[4], void *font);void showInfo();void showTransferRate();void printTransferRate();void draw();void add(unsigned char* src, int width, int height, int shift, unsigned char* dst);void toOrtho();void toPerspective();// constantsconst int SCREEN_WIDTH = 256;const int SCREEN_HEIGHT = 256;const int CHANNEL_COUNT = 4;const int DATA_SIZE = SCREEN_WIDTH * SCREEN_HEIGHT * CHANNEL_COUNT;const GLenum PIXEL_FORMAT = GL_BGRA;const int PBO_COUNT = 2;// global variablesvoid *font = GLUT_BITMAP_8_BY_13;GLuint pboIds[PBO_COUNT]; // IDs of PBOsbool mouseLeftDown;bool mouseRightDown;float mouseX, mouseY;float cameraAngleX;float cameraAngleY;float cameraDistance;bool pboSupported;bool pboUsed;int drawMode = 0;Timer timer, t1;float readTime, processTime;GLubyte* colorBuffer = 0;// function pointers for PBO Extension// Windows needs to get function pointers from ICD OpenGL drivers,// because opengl32.dll does not support extensions higher than v1.1.#ifdef _WIN32PFNGLGENBUFFERSARBPROC pglGenBuffersARB = 0; // VBO Name Generation ProcedurePFNGLBINDBUFFERARBPROC pglBindBufferARB = 0; // VBO Bind ProcedurePFNGLBUFFERDATAARBPROC pglBufferDataARB = 0; // VBO Data Loading ProcedurePFNGLBUFFERSUBDATAARBPROC pglBufferSubDataARB = 0;// VBO Sub Data Loading ProcedurePFNGLDELETEBUFFERSARBPROC pglDeleteBuffersARB = 0;// VBO Deletion ProcedurePFNGLGETBUFFERPARAMETERIVARBPROC pglGetBufferParameterivARB = 0; // return various parameters of VBOPFNGLMAPBUFFERARBPROC pglMapBufferARB = 0;   // map VBO procedurePFNGLUNMAPBUFFERARBPROC pglUnmapBufferARB = 0;    // unmap VBO procedure#define glGenBuffersARB pglGenBuffersARB#define glBindBufferARB pglBindBufferARB#define glBufferDataARB pglBufferDataARB#define glBufferSubDataARB   pglBufferSubDataARB#define glDeleteBuffersARB   pglDeleteBuffersARB#define glGetBufferParameterivARB pglGetBufferParameterivARB#define glMapBufferARB  pglMapBufferARB#define glUnmapBufferARBpglUnmapBufferARB#endif///////////////////////////////////////////////////////////////////////////////// draw a cube with immediate mode// 54 calls = 24 glVertex*() calls + 24 glColor*() calls + 6 glNormal*() calls///////////////////////////////////////////////////////////////////////////////void draw(){    glBegin(GL_QUADS);   // face v0-v1-v2-v3   glNormal3f(0,0,1);   glColor3f(1,1,1);   glVertex3f(1,1,1);   glColor3f(1,1,0);   glVertex3f(-1,1,1);   glColor3f(1,0,0);   glVertex3f(-1,-1,1);   glColor3f(1,0,1);   glVertex3f(1,-1,1);   // face v0-v3-v4-v6   glNormal3f(1,0,0);   glColor3f(1,1,1);   glVertex3f(1,1,1);   glColor3f(1,0,1);   glVertex3f(1,-1,1);   glColor3f(0,0,1);   glVertex3f(1,-1,-1);   glColor3f(0,1,1);   glVertex3f(1,1,-1);   // face v0-v5-v6-v1   glNormal3f(0,1,0);   glColor3f(1,1,1);   glVertex3f(1,1,1);   glColor3f(0,1,1);   glVertex3f(1,1,-1);   glColor3f(0,1,0);   glVertex3f(-1,1,-1);   glColor3f(1,1,0);   glVertex3f(-1,1,1);   // face  v1-v6-v7-v2   glNormal3f(-1,0,0);   glColor3f(1,1,0);   glVertex3f(-1,1,1);   glColor3f(0,1,0);   glVertex3f(-1,1,-1);   glColor3f(0,0,0);   glVertex3f(-1,-1,-1);   glColor3f(1,0,0);   glVertex3f(-1,-1,1);   // face v7-v4-v3-v2   glNormal3f(0,-1,0);   glColor3f(0,0,0);   glVertex3f(-1,-1,-1);   glColor3f(0,0,1);   glVertex3f(1,-1,-1);   glColor3f(1,0,1);   glVertex3f(1,-1,1);   glColor3f(1,0,0);   glVertex3f(-1,-1,1);   // face v4-v7-v6-v5   glNormal3f(0,0,-1);   glColor3f(0,0,1);   glVertex3f(1,-1,-1);   glColor3f(0,0,0);   glVertex3f(-1,-1,-1);   glColor3f(0,1,0);   glVertex3f(-1,1,-1);   glColor3f(0,1,1);   glVertex3f(1,1,-1);    glEnd();}///////////////////////////////////////////////////////////////////////////////int main(int argc, char **argv){    initSharedMem();    // init GLUT and GL    initGLUT(argc, argv);    initGL();    // get OpenGL info    glInfo glInfo;    glInfo.getInfo();    glInfo.printSelf();#ifdef _WIN32    // check PBO is supported by your video card    if(glInfo.isExtensionSupported("GL_ARB_pixel_buffer_object"))    {   // get pointers to GL functions   glGenBuffersARB = (PFNGLGENBUFFERSARBPROC)wglGetProcAddress("glGenBuffersARB");   glBindBufferARB = (PFNGLBINDBUFFERARBPROC)wglGetProcAddress("glBindBufferARB");   glBufferDataARB = (PFNGLBUFFERDATAARBPROC)wglGetProcAddress("glBufferDataARB");   glBufferSubDataARB = (PFNGLBUFFERSUBDATAARBPROC)wglGetProcAddress("glBufferSubDataARB");   glDeleteBuffersARB = (PFNGLDELETEBUFFERSARBPROC)wglGetProcAddress("glDeleteBuffersARB");   glGetBufferParameterivARB = (PFNGLGETBUFFERPARAMETERIVARBPROC)wglGetProcAddress("glGetBufferParameterivARB");   glMapBufferARB = (PFNGLMAPBUFFERARBPROC)wglGetProcAddress("glMapBufferARB");   glUnmapBufferARB = (PFNGLUNMAPBUFFERARBPROC)wglGetProcAddress("glUnmapBufferARB");   // check once again PBO extension   if(glGenBuffersARB && glBindBufferARB && glBufferDataARB && glBufferSubDataARB && glMapBufferARB && glUnmapBufferARB && glDeleteBuffersARB && glGetBufferParameterivARB)   {  pboSupported = pboUsed = true;  cout << "Video card supports GL_ARB_pixel_buffer_object." << endl;   }   else   {  pboSupported = pboUsed = false;  cout << "Video card does NOT support GL_ARB_pixel_buffer_object." << endl;   }    }#else // for linux, do not need to get function pointers, it is up-to-date    if(glInfo.isExtensionSupported("GL_ARB_pixel_buffer_object"))    {   pboSupported = pboUsed = true;   cout << "Video card supports GL_ARB_pixel_buffer_object." << endl;    }    else    {   pboSupported = pboUsed = false;   cout << "Video card does NOT support GL_ARB_pixel_buffer_object." << endl;    }#endif    if(pboSupported)    {   // create 2 pixel buffer objects, you need to delete them when program exits.   // glBufferDataARB with NULL pointer reserves only memory space.   glGenBuffersARB(PBO_COUNT, pboIds);   glBindBufferARB(GL_PIXEL_PACK_BUFFER_ARB, pboIds[0]);   glBufferDataARB(GL_PIXEL_PACK_BUFFER_ARB, DATA_SIZE, 0, GL_STREAM_READ_ARB);   glBindBufferARB(GL_PIXEL_PACK_BUFFER_ARB, pboIds[1]);   glBufferDataARB(GL_PIXEL_PACK_BUFFER_ARB, DATA_SIZE, 0, GL_STREAM_READ_ARB);   glBindBufferARB(GL_PIXEL_PACK_BUFFER_ARB, 0);    }    // start timer, the elapsed time will be used for updateVertices()    timer.start();    // the last GLUT call (LOOP)    // window will be shown and display callback is triggered by events    // NOTE: this call never return main().    glutMainLoop(); /* Start GLUT event-processing loop */    return 0;}///////////////////////////////////////////////////////////////////////////////// initialize GLUT for windowing///////////////////////////////////////////////////////////////////////////////int initGLUT(int argc, char **argv){    // GLUT stuff for windowing    // initialization openGL window.    // it is called before any other GLUT routine    glutInit(&argc, argv);    glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_ALPHA); // display mode    glutInitWindowSize(SCREEN_WIDTH*2, SCREEN_HEIGHT);    // window size    glutInitWindowPosition(100, 100); // window location    // finally, create a window with openGL context    // Window will not displayed until glutMainLoop() is called    // it returns a unique ID    int handle = glutCreateWindow(argv[0]);// param is the title of window    // register GLUT callback functions    glutDisplayFunc(displayCB);    //glutTimerFunc(33, timerCB, 33);   // redraw only every given millisec    glutIdleFunc(idleCB);   // redraw only every given millisec    glutReshapeFunc(reshapeCB);    glutKeyboardFunc(keyboardCB);    glutMouseFunc(mouseCB);    glutMotionFunc(mouseMotionCB);    return handle;}///////////////////////////////////////////////////////////////////////////////// initialize OpenGL// disable unused features///////////////////////////////////////////////////////////////////////////////void initGL(){    glShadeModel(GL_SMOOTH);// shading mathod: GL_SMOOTH or GL_FLAT    glPixelStorei(GL_UNPACK_ALIGNMENT, 4); // 4-byte pixel alignment    // enable /disable features    glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST);    //glHint(GL_LINE_SMOOTH_HINT, GL_NICEST);    //glHint(GL_POLYGON_SMOOTH_HINT, GL_NICEST);    glEnable(GL_DEPTH_TEST);    glEnable(GL_LIGHTING);    glEnable(GL_TEXTURE_2D);    glEnable(GL_CULL_FACE);// track material ambient and diffuse from surface color, call it before glEnable(GL_COLOR_MATERIAL)    glColorMaterial(GL_FRONT_AND_BACK, GL_AMBIENT_AND_DIFFUSE);    glEnable(GL_COLOR_MATERIAL);    glClearColor(0, 0, 0, 0);    // background color    glClearStencil(0); // clear stencil buffer    glClearDepth(1.0f);// 0 is near, 1 is far    glDepthFunc(GL_LEQUAL);    initLights();    //setCamera(0, 0, 8, 0, 0, 0);}///////////////////////////////////////////////////////////////////////////////// write 2d text using GLUT// The projection matrix must be set to orthogonal before call this function.///////////////////////////////////////////////////////////////////////////////void drawString(const char *str, int x, int y, float color[4], void *font){    glPushAttrib(GL_LIGHTING_BIT | GL_CURRENT_BIT); // lighting and color mask    glDisable(GL_LIGHTING);// need to disable lighting for proper text color    glDisable(GL_TEXTURE_2D);    glColor4fv(color);// set text color    glRasterPos2i(x, y);   // place text position    // loop all characters in the string    while(*str)    {   glutBitmapCharacter(font, *str);   ++str;    }    glEnable(GL_TEXTURE_2D);    glEnable(GL_LIGHTING);    glPopAttrib();}///////////////////////////////////////////////////////////////////////////////// draw a string in 3D space///////////////////////////////////////////////////////////////////////////////void drawString3D(const char *str, float pos[3], float color[4], void *font){    glPushAttrib(GL_LIGHTING_BIT | GL_CURRENT_BIT); // lighting and color mask    glDisable(GL_LIGHTING);// need to disable lighting for proper text color    glColor4fv(color);// set text color    glRasterPos3fv(pos);   // place text position    // loop all characters in the string    while(*str)    {   glutBitmapCharacter(font, *str);   ++str;    }    glEnable(GL_LIGHTING);    glPopAttrib();}///////////////////////////////////////////////////////////////////////////////// initialize global variables///////////////////////////////////////////////////////////////////////////////bool initSharedMem(){    mouseLeftDown = mouseRightDown = false;    // allocate buffers to store frames    colorBuffer = new GLubyte[DATA_SIZE];    memset(colorBuffer, 255, DATA_SIZE);    return true;}///////////////////////////////////////////////////////////////////////////////// clean up shared memory///////////////////////////////////////////////////////////////////////////////void clearSharedMem(){    // deallocate frame buffer    delete [] colorBuffer;    colorBuffer = 0;    // clean up PBOs    if(pboSupported)    {   glDeleteBuffersARB(PBO_COUNT, pboIds);    }}///////////////////////////////////////////////////////////////////////////////// initialize lights///////////////////////////////////////////////////////////////////////////////void initLights(){    // set up light colors (ambient, diffuse, specular)    GLfloat lightKa[] = {.2f, .2f, .2f, 1.0f};  // ambient light    GLfloat lightKd[] = {.7f, .7f, .7f, 1.0f};  // diffuse light    GLfloat lightKs[] = {1, 1, 1, 1}; // specular light    glLightfv(GL_LIGHT0, GL_AMBIENT, lightKa);    glLightfv(GL_LIGHT0, GL_DIFFUSE, lightKd);    glLightfv(GL_LIGHT0, GL_SPECULAR, lightKs);    // position the light    float lightPos[4] = {0, 0, 20, 1}; // positional light    glLightfv(GL_LIGHT0, GL_POSITION, lightPos);    glEnable(GL_LIGHT0);    // MUST enable each light source after configuration}///////////////////////////////////////////////////////////////////////////////// set camera position and lookat direction///////////////////////////////////////////////////////////////////////////////void setCamera(float posX, float posY, float posZ, float targetX, float targetY, float targetZ){    glMatrixMode(GL_MODELVIEW);    glLoadIdentity();    gluLookAt(posX, posY, posZ, targetX, targetY, targetZ, 0, 1, 0); // eye(x,y,z), focal(x,y,z), up(x,y,z)}///////////////////////////////////////////////////////////////////////////////// display info messages///////////////////////////////////////////////////////////////////////////////void showInfo(){    // backup current model-view matrix    glPushMatrix(); // save current modelview matrix    glLoadIdentity();    // reset modelview matrix    // set to 2D orthogonal projection    glMatrixMode(GL_PROJECTION);// switch to projection matrix    glPushMatrix();   // save current projection matrix    glLoadIdentity(); // reset projection matrix    gluOrtho2D(0, SCREEN_WIDTH, 0, SCREEN_HEIGHT);  // set to orthogonal projection    const int FONT_HEIGHT = 14;    float color[4] = {1, 1, 1, 1};    stringstream ss;    ss << "PBO: ";    if(pboUsed)   ss << "on" << ends;    else   ss << "off" << ends;    drawString(ss.str().c_str(), 1, SCREEN_HEIGHT-FONT_HEIGHT, color, font);    ss.str(""); // clear buffer    ss << "Read Time: " << readTime << " ms" << ends;    drawString(ss.str().c_str(), 1, SCREEN_HEIGHT-(2*FONT_HEIGHT), color, font);    ss.str("");    ss << std::fixed << std::setprecision(3);    ss << "Process Time: " << processTime << " ms" << ends;    drawString(ss.str().c_str(), 1, SCREEN_HEIGHT-(3*FONT_HEIGHT), color, font);    ss.str("");    ss << "Press SPACE to toggle PBO." << ends;    drawString(ss.str().c_str(), 1, 1, color, font);    // unset floating format    ss << std::resetiosflags(std::ios_base::fixed | std::ios_base::floatfield);    // restore projection matrix    glPopMatrix();    // restore to previous projection matrix    // restore modelview matrix    glMatrixMode(GL_MODELVIEW); // switch to modelview matrix    glPopMatrix();    // restore to previous modelview matrix}///////////////////////////////////////////////////////////////////////////////// display transfer rates///////////////////////////////////////////////////////////////////////////////void showTransferRate(){    static Timer timer;    static int count = 0;    static stringstream ss;    double elapsedTime;    // backup current model-view matrix    glPushMatrix(); // save current modelview matrix    glLoadIdentity();    // reset modelview matrix    // set to 2D orthogonal projection    glMatrixMode(GL_PROJECTION);   // switch to projection matrix    glPushMatrix(); // save current projection matrix    glLoadIdentity();    // reset projection matrix    gluOrtho2D(0, SCREEN_WIDTH, 0, SCREEN_HEIGHT); // set to orthogonal projection    float color[4] = {1, 1, 0, 1};    // update fps every second    elapsedTime = timer.getElapsedTime();    if(elapsedTime < 1.0)    {   ++count;    }    else    {   ss.str("");   ss << std::fixed << std::setprecision(1);   ss << "Transfer Rate: " << (count / elapsedTime) * (SCREEN_WIDTH * SCREEN_HEIGHT) / (1024 * 1024) << " Mp" << ends; // update fps string   ss << std::resetiosflags(std::ios_base::fixed | std::ios_base::floatfield);   count = 0;  // reset counter   timer.start();   // restart timer    }    drawString(ss.str().c_str(), 200, 286, color, font);    // restore projection matrix    glPopMatrix();  // restore to previous projection matrix    // restore modelview matrix    glMatrixMode(GL_MODELVIEW);    // switch to modelview matrix    glPopMatrix();  // restore to previous modelview matrix}///////////////////////////////////////////////////////////////////////////////// print transfer rates///////////////////////////////////////////////////////////////////////////////void printTransferRate(){    const double INV_MEGA = 1.0 / (1024 * 1024);    static Timer timer;    static int count = 0;    static stringstream ss;    double elapsedTime;    // loop until 1 sec passed    elapsedTime = timer.getElapsedTime();    if(elapsedTime < 1.0)    {   ++count;    }    else    {   cout << std::fixed << std::setprecision(1);   cout << "Transfer Rate: " << (count / elapsedTime) * (SCREEN_WIDTH * SCREEN_HEIGHT) * INV_MEGA << " Mpixels/s. (" << count / elapsedTime << " FPS)\n";   cout << std::resetiosflags(std::ios_base::fixed | std::ios_base::floatfield);   count = 0;  // reset counter   timer.start();   // restart timer    }}///////////////////////////////////////////////////////////////////////////////// change the brightness///////////////////////////////////////////////////////////////////////////////void add(unsigned char* src, int width, int height, int shift, unsigned char* dst){    if(!src || !dst)   return;    int value;    for(int i = 0; i < height; ++i)    {   for(int j = 0; j < width; ++j)   {  value = *src + shift;  if(value > 255) *dst = (unsigned char)255;  else  *dst = (unsigned char)value;  ++src;  ++dst;  value = *src + shift;  if(value > 255) *dst = (unsigned char)255;  else  *dst = (unsigned char)value;  ++src;  ++dst;  value = *src + shift;  if(value > 255) *dst = (unsigned char)255;  else  *dst = (unsigned char)value;  ++src;  ++dst;  ++src;    // skip alpha  ++dst;   }    }}void toOrtho(){    // set viewport to be the entire window    glViewport((GLsizei)SCREEN_WIDTH, 0, (GLsizei)SCREEN_WIDTH, (GLsizei)SCREEN_HEIGHT);    // set orthographic viewing frustum    glMatrixMode(GL_PROJECTION);    glLoadIdentity();    glOrtho(0, SCREEN_WIDTH, 0, SCREEN_HEIGHT, -1, 1);    // switch to modelview matrix in order to set scene    glMatrixMode(GL_MODELVIEW);    glLoadIdentity();    gluLookAt(0, 0, 0, 0, 0, -1, 0, 1, 0); // eye(x,y,z), focal(x,y,z), up(x,y,z)}void toPerspective(){    // set viewport to be the entire window    glViewport(0, 0, (GLsizei)SCREEN_WIDTH, (GLsizei)SCREEN_HEIGHT);    // set perspective viewing frustum    glMatrixMode(GL_PROJECTION);    glLoadIdentity();    gluPerspective(60.0f, (float)(SCREEN_WIDTH)/SCREEN_HEIGHT, 1.0f, 1000.0f); // FOV, AspectRatio, NearClip, FarClip    // switch to modelview matrix in order to set scene    glMatrixMode(GL_MODELVIEW);    glLoadIdentity();    gluLookAt(0, 0, 8, 0, 0, 0, 0, 1, 0); // eye(x,y,z), focal(x,y,z), up(x,y,z)}//=============================================================================// CALLBACKS//=============================================================================void displayCB(){    static int shift = 0;    static int index = 0;    int nextIndex = 0;   // pbo index used for next frame    // brightness shift amount    shift = ++shift % 200;    // increment current index first then get the next index    // "index" is used to read pixels from a framebuffer to a PBO    // "nextIndex" is used to process pixels in the other PBO    index = (index + 1) % 2;    nextIndex = (index + 1) % 2;    // set the framebuffer to read    glReadBuffer(GL_FRONT);    if(pboUsed) // with PBO    {   // read framebuffer ///////////////////////////////   t1.start();   // copy pixels from framebuffer to PBO   // Use offset instead of ponter.   // OpenGL should perform asynch DMA transfer, so glReadPixels() will return immediately.   glBindBufferARB(GL_PIXEL_PACK_BUFFER_ARB, pboIds[index]);   glReadPixels(0, 0, SCREEN_WIDTH, SCREEN_HEIGHT, PIXEL_FORMAT, GL_UNSIGNED_BYTE, 0);   // measure the time reading framebuffer   t1.stop();   readTime = t1.getElapsedTimeInMilliSec();   ///////////////////////////////////////////////////   // process pixel data /////////////////////////////   t1.start();   // map the PBO that contain framebuffer pixels before processing it   glBindBufferARB(GL_PIXEL_PACK_BUFFER_ARB, pboIds[nextIndex]);   GLubyte* src = (GLubyte*)glMapBufferARB(GL_PIXEL_PACK_BUFFER_ARB, GL_READ_ONLY_ARB);   if(src)   {  // change brightness  add(src, SCREEN_WIDTH, SCREEN_HEIGHT, shift, colorBuffer);  glUnmapBufferARB(GL_PIXEL_PACK_BUFFER_ARB);// release pointer to the mapped buffer   }   // measure the time reading framebuffer   t1.stop();   processTime = t1.getElapsedTimeInMilliSec();   ///////////////////////////////////////////////////   glBindBufferARB(GL_PIXEL_PACK_BUFFER_ARB, 0);    }    else   // without PBO    {   // read framebuffer ///////////////////////////////   t1.start();   glReadPixels(0, 0, SCREEN_WIDTH, SCREEN_HEIGHT, PIXEL_FORMAT, GL_UNSIGNED_BYTE, colorBuffer);   // measure the time reading framebuffer   t1.stop();   readTime = t1.getElapsedTimeInMilliSec();   ///////////////////////////////////////////////////   // covert to greyscale ////////////////////////////   t1.start();   // change brightness   add(colorBuffer, SCREEN_WIDTH, SCREEN_HEIGHT, shift, colorBuffer);   // measure the time reading framebuffer   t1.stop();   processTime = t1.getElapsedTimeInMilliSec();   ///////////////////////////////////////////////////    }    // render to the framebuffer //////////////////////////    glDrawBuffer(GL_BACK);    toPerspective(); // set to perspective on the left side of the window    // clear buffer    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);    // tramsform camera    glTranslatef(0, 0, cameraDistance);    glRotatef(cameraAngleX, 1, 0, 0);   // pitch    glRotatef(cameraAngleY, 0, 1, 0);   // heading    // draw a cube    draw();    // draw the read color buffer to the right side of the window    toOrtho(); // set to orthographic on the right side of the window    glRasterPos2i(0, 0);    glDrawPixels(SCREEN_WIDTH, SCREEN_HEIGHT, PIXEL_FORMAT, GL_UNSIGNED_BYTE, colorBuffer);    // draw info messages    showInfo();    printTransferRate();    glutSwapBuffers();}void reshapeCB(int w, int h){    toPerspective();}void timerCB(int millisec){    glutTimerFunc(millisec, timerCB, millisec);    glutPostRedisplay();}void idleCB(){    glutPostRedisplay();}void keyboardCB(unsigned char key, int x, int y){    switch(key)    {    case 27: // ESCAPE   clearSharedMem();   //exit(0);   break;    case ' ':   if(pboSupported)  pboUsed = !pboUsed;   cout << "PBO mode: " << (pboUsed ? "on" : "off") << endl;    break;    case 'd': // switch rendering modes (fill -> wire -> point)    case 'D':   drawMode = ++drawMode % 3;   if(drawMode == 0)   // fill mode   {  glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);  glEnable(GL_DEPTH_TEST);  glEnable(GL_CULL_FACE);   }   else if(drawMode == 1)  // wireframe mode   {  glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);  glDisable(GL_DEPTH_TEST);  glDisable(GL_CULL_FACE);   }   else// point mode   {  glPolygonMode(GL_FRONT_AND_BACK, GL_POINT);  glDisable(GL_DEPTH_TEST);  glDisable(GL_CULL_FACE);   }   break;    default:   ;    }    glutPostRedisplay();}void mouseCB(int button, int state, int x, int y){    mouseX = x;    mouseY = y;    if(button == GLUT_LEFT_BUTTON)    {   if(state == GLUT_DOWN)   {  mouseLeftDown = true;   }   else if(state == GLUT_UP)  mouseLeftDown = false;    }    else if(button == GLUT_RIGHT_BUTTON)    {   if(state == GLUT_DOWN)   {  mouseRightDown = true;   }   else if(state == GLUT_UP)  mouseRightDown = false;    }}void mouseMotionCB(int x, int y){    if(mouseLeftDown)    {   cameraAngleY += (x - mouseX);   cameraAngleX += (y - mouseY);   mouseX = x;   mouseY = y;    }    if(mouseRightDown)    {   cameraDistance += (y - mouseY) * 0.2f;   mouseY = y;    }}================================================================================================================================================================3. Third technique is using plain Windows Code (WinMain) - Read Time: 0.01ms   ==========================================================================/* *This Code Was Created By Jeff Molofee 2000 *A HUGE Thanks To Fredric Echols For Cleaning Up *And Optimizing The Base Code, Making It More Flexible! *If You've Found This Code Useful, Please Let Me Know. *Visit My Site At nehe.gamedev.net */// in order to get function prototypes from glext.h, define GL_GLEXT_PROTOTYPES before including glext.h#define GL_GLEXT_PROTOTYPES#include <windows.h>// Header File For Windows#include <gl\gl.h>// Header File For The OpenGL32 Library#include <gl\glu.h>// Header File For The GLu32 Library#include "glut.h"//#include <gl\glaux.h>// Header File For The Glaux Library#include "oglext\glext.h"#include <iostream>#include <sstream>#include <iomanip>#include "glInfo.h"    // glInfo struct#include "Timer.h"using std::stringstream;using std::cout;using std::endl;using std::ends;// VBO Extension Definitions, From glext.h#define GL_ARRAY_BUFFER_ARB 0x8892#define GL_STATIC_DRAW_ARB 0x88E4typedef void (APIENTRY * PFNGLBINDBUFFERARBPROC) (GLenum target, GLuint buffer);typedef void (APIENTRY * PFNGLDELETEBUFFERSARBPROC) (GLsizei n, const GLuint *buffers);typedef void (APIENTRY * PFNGLGENBUFFERSARBPROC) (GLsizei n, GLuint *buffers);typedef void (APIENTRY * PFNGLBUFFERDATAARBPROC) (GLenum target, int size, const GLvoid *data, GLenum usage);typedef void (APIENTRY * PFNGLBUFFERSUBDATAARBPROC) (GLenum, GLintptrARB, GLsizeiptrARB, GLvoid const *);typedef void (APIENTRY * PFNGLGETBUFFERPARAMETERIVARBPROC) (GLenum, GLenum, GLint *);typedef GLvoid* (APIENTRY * PFNGLMAPBUFFERARBPROC) (GLenum, GLenum);typedef GLboolean* (APIENTRY * PFNGLUNMAPBUFFERARBPROC) (GLenum);HDChDC=NULL;// Private GDI Device ContextHGLRChRC=NULL;// Permanent Rendering ContextHWNDhWnd=NULL;// Holds Our Window HandleHINSTANCEhInstance;// Holds The Instance Of The Applicationboolkeys[256];// Array Used For The Keyboard Routineboolactive=TRUE;// Window Active Flag Set To TRUE By Defaultboolfullscreen=TRUE;// Fullscreen Flag Set To Fullscreen Mode By DefaultGLfloatrtri;// Angle For The Triangle ( NEW )GLfloatrquad;// Angle For The Quad ( NEW )// function pointers for PBO Extension// Windows needs to get function pointers from ICD OpenGL drivers,// because opengl32.dll does not support extensions higher than v1.1.#ifdef _WIN32PFNGLGENBUFFERSARBPROC pglGenBuffersARB = 0; // VBO Name Generation ProcedurePFNGLBINDBUFFERARBPROC pglBindBufferARB = 0; // VBO Bind ProcedurePFNGLBUFFERDATAARBPROC pglBufferDataARB = 0; // VBO Data Loading ProcedurePFNGLBUFFERSUBDATAARBPROC pglBufferSubDataARB = 0;// VBO Sub Data Loading ProcedurePFNGLDELETEBUFFERSARBPROC pglDeleteBuffersARB = 0;// VBO Deletion ProcedurePFNGLGETBUFFERPARAMETERIVARBPROC pglGetBufferParameterivARB = 0; // return various parameters of VBOPFNGLMAPBUFFERARBPROC pglMapBufferARB = 0;   // map VBO procedurePFNGLUNMAPBUFFERARBPROC pglUnmapBufferARB = 0;    // unmap VBO procedure#define glGenBuffersARB pglGenBuffersARB#define glBindBufferARB pglBindBufferARB#define glBufferDataARB pglBufferDataARB#define glBufferSubDataARB   pglBufferSubDataARB#define glDeleteBuffersARB   pglDeleteBuffersARB#define glGetBufferParameterivARB pglGetBufferParameterivARB#define glMapBufferARB  pglMapBufferARB#define glUnmapBufferARBpglUnmapBufferARB#endif// constantsconst int SCREEN_WIDTH = 256;const int SCREEN_HEIGHT = 256;const int CHANNEL_COUNT = 4;const int DATA_SIZE = SCREEN_WIDTH * SCREEN_HEIGHT * CHANNEL_COUNT;const GLenum PIXEL_FORMAT = GL_BGRA;const int PBO_COUNT = 2;// global variablesvoid *font = GLUT_BITMAP_8_BY_13;bool pboSupported;GLubyte* colorBuffer = 0;bool pboUsed;GLuint pboIds[PBO_COUNT]; // IDs of PBOsfloat cameraAngleX;float cameraAngleY;float cameraDistance;Timer timer, t1;float readTime, processTime;// GLUT CALLBACK functionsvoid displayCB();void reshapeCB(int w, int h);void timerCB(int millisec);void idleCB();void keyboardCB(unsigned char key, int x, int y);void mouseCB(int button, int stat, int x, int y);void mouseMotionCB(int x, int y);bool mouseLeftDown;bool mouseRightDown;float mouseX, mouseY;int drawMode = 0;LRESULTCALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);// Declaration For WndProc///////////////////////////////////////////////////////////////////////////////// initialize global variables//////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////// clean up shared memory///////////////////////////////////////////////////////////////////////////////void clearSharedMem(){    // deallocate frame buffer    delete [] colorBuffer;    colorBuffer = 0;    // clean up PBOs    if(pboSupported)    {   glDeleteBuffersARB(PBO_COUNT, pboIds);    }}bool initSharedMem(){    mouseLeftDown = mouseRightDown = false;    // allocate buffers to store frames    colorBuffer = new GLubyte[DATA_SIZE];    memset(colorBuffer, 255, DATA_SIZE);    return true;}///////////////////////////////////////////////////////////////////////////////// write 2d text using GLUT// The projection matrix must be set to orthogonal before call this function.///////////////////////////////////////////////////////////////////////////////void drawString(const char *str, int x, int y, float color[4], void *font){    glPushAttrib(GL_LIGHTING_BIT | GL_CURRENT_BIT); // lighting and color mask    glDisable(GL_LIGHTING);// need to disable lighting for proper text color    glDisable(GL_TEXTURE_2D);    glColor4fv(color);// set text color    glRasterPos2i(x, y);   // place text position    // loop all characters in the string    while(*str)    {   glutBitmapCharacter(font, *str);   ++str;    }    glEnable(GL_TEXTURE_2D);    glEnable(GL_LIGHTING);    glPopAttrib();}///////////////////////////////////////////////////////////////////////////////// display info messages///////////////////////////////////////////////////////////////////////////////void showInfo(){    // backup current model-view matrix    glPushMatrix(); // save current modelview matrix    glLoadIdentity();    // reset modelview matrix    // set to 2D orthogonal projection    glMatrixMode(GL_PROJECTION);// switch to projection matrix    glPushMatrix();   // save current projection matrix    glLoadIdentity(); // reset projection matrix    gluOrtho2D(0, SCREEN_WIDTH, 0, SCREEN_HEIGHT);  // set to orthogonal projection    const int FONT_HEIGHT = 14;    float color[4] = {1, 1, 1, 1};    stringstream ss;    ss << "PBO: ";    if(pboUsed)   ss << "on" << ends;    else   ss << "off" << ends;    drawString(ss.str().c_str(), 1, SCREEN_HEIGHT-FONT_HEIGHT, color, font);    ss.str(""); // clear buffer    ss << "Read Time: " << readTime << " ms" << ends;    drawString(ss.str().c_str(), 1, SCREEN_HEIGHT-(2*FONT_HEIGHT), color, font);    ss.str("");    ss << std::fixed << std::setprecision(3);    ss << "Process Time: " << processTime << " ms" << ends;    drawString(ss.str().c_str(), 1, SCREEN_HEIGHT-(3*FONT_HEIGHT), color, font);    ss.str("");    ss << "Press SPACE to toggle PBO." << ends;    drawString(ss.str().c_str(), 1, 1, color, font);    // unset floating format    ss << std::resetiosflags(std::ios_base::fixed | std::ios_base::floatfield);    // restore projection matrix    glPopMatrix();    // restore to previous projection matrix    // restore modelview matrix    glMatrixMode(GL_MODELVIEW); // switch to modelview matrix    glPopMatrix();    // restore to previous modelview matrix}///////////////////////////////////////////////////////////////////////////////// display transfer rates///////////////////////////////////////////////////////////////////////////////void showTransferRate(){    static Timer timer;    static int count = 0;    static stringstream ss;    double elapsedTime;    // backup current model-view matrix    glPushMatrix(); // save current modelview matrix    glLoadIdentity();    // reset modelview matrix    // set to 2D orthogonal projection    glMatrixMode(GL_PROJECTION);   // switch to projection matrix    glPushMatrix(); // save current projection matrix    glLoadIdentity();    // reset projection matrix    gluOrtho2D(0, SCREEN_WIDTH, 0, SCREEN_HEIGHT); // set to orthogonal projection    float color[4] = {1, 1, 0, 1};    // update fps every second    elapsedTime = timer.getElapsedTime();    if(elapsedTime < 1.0)    {   ++count;    }    else    {   ss.str("");   ss << std::fixed << std::setprecision(1);   ss << "Transfer Rate: " << (count / elapsedTime) * (SCREEN_WIDTH * SCREEN_HEIGHT) / (1024 * 1024) << " Mp" << ends; // update fps string   ss << std::resetiosflags(std::ios_base::fixed | std::ios_base::floatfield);   count = 0;  // reset counter   timer.start();   // restart timer    }    drawString(ss.str().c_str(), 200, 286, color, font);    // restore projection matrix    glPopMatrix();  // restore to previous projection matrix    // restore modelview matrix    glMatrixMode(GL_MODELVIEW);    // switch to modelview matrix    glPopMatrix();  // restore to previous modelview matrix}///////////////////////////////////////////////////////////////////////////////// print transfer rates///////////////////////////////////////////////////////////////////////////////void printTransferRate(){    const double INV_MEGA = 1.0 / (1024 * 1024);    static Timer timer;    static int count = 0;    static stringstream ss;    double elapsedTime;    // loop until 1 sec passed    elapsedTime = timer.getElapsedTime();    if(elapsedTime < 1.0)    {   ++count;    }    else    {   cout << std::fixed << std::setprecision(1);   cout << "Transfer Rate: " << (count / elapsedTime) * (SCREEN_WIDTH * SCREEN_HEIGHT) * INV_MEGA << " Mpixels/s. (" << count / elapsedTime << " FPS)\n";   cout << std::resetiosflags(std::ios_base::fixed | std::ios_base::floatfield);   count = 0;  // reset counter   timer.start();   // restart timer    }}GLvoid ReSizeGLScene(GLsizei width, GLsizei height)// Resize And Initialize The GL Window{if (height==0)// Prevent A Divide By Zero By{height=1;// Making Height Equal One}glViewport(0,0,width,height);// Reset The Current ViewportglMatrixMode(GL_PROJECTION);// Select The Projection MatrixglLoadIdentity();// Reset The Projection Matrix// Calculate The Aspect Ratio Of The WindowgluPerspective(45.0f,(GLfloat)width/(GLfloat)height,0.1f,100.0f);glMatrixMode(GL_MODELVIEW);// Select The Modelview MatrixglLoadIdentity();// Reset The Modelview Matrix}int InitGL(GLvoid)// All Setup For OpenGL Goes Here{initSharedMem();// get OpenGL info    glInfo glInfo;    glInfo.getInfo();    glInfo.printSelf();#ifdef _WIN32    // check PBO is supported by your video card    if(glInfo.isExtensionSupported("GL_ARB_pixel_buffer_object"))    {   // get pointers to GL functions   glGenBuffersARB = (PFNGLGENBUFFERSARBPROC)wglGetProcAddress("glGenBuffersARB");   glBindBufferARB = (PFNGLBINDBUFFERARBPROC)wglGetProcAddress("glBindBufferARB");   glBufferDataARB = (PFNGLBUFFERDATAARBPROC)wglGetProcAddress("glBufferDataARB");   glBufferSubDataARB = (PFNGLBUFFERSUBDATAARBPROC)wglGetProcAddress("glBufferSubDataARB");   glDeleteBuffersARB = (PFNGLDELETEBUFFERSARBPROC)wglGetProcAddress("glDeleteBuffersARB");   glGetBufferParameterivARB = (PFNGLGETBUFFERPARAMETERIVARBPROC)wglGetProcAddress("glGetBufferParameterivARB");   glMapBufferARB = (PFNGLMAPBUFFERARBPROC)wglGetProcAddress("glMapBufferARB");   glUnmapBufferARB = (PFNGLUNMAPBUFFERARBPROC)wglGetProcAddress("glUnmapBufferARB");   // check once again PBO extension   if(glGenBuffersARB && glBindBufferARB && glBufferDataARB && glBufferSubDataARB && glMapBufferARB && glUnmapBufferARB && glDeleteBuffersARB && glGetBufferParameterivARB)   {  pboSupported = pboUsed = true;  //cout << "Video card supports GL_ARB_pixel_buffer_object." << endl;   }   else   {  pboSupported = pboUsed = false; // cout << "Video card does NOT support GL_ARB_pixel_buffer_object." << endl;   }    }#else // for linux, do not need to get function pointers, it is up-to-date    if(glInfo.isExtensionSupported("GL_ARB_pixel_buffer_object"))    {   pboSupported = pboUsed = true;   cout << "Video card supports GL_ARB_pixel_buffer_object." << endl;    }    else    {   pboSupported = pboUsed = false;   cout << "Video card does NOT support GL_ARB_pixel_buffer_object." << endl;    }#endifif(pboSupported)    {   // create 2 pixel buffer objects, you need to delete them when program exits.   // glBufferDataARB with NULL pointer reserves only memory space.   glGenBuffersARB(PBO_COUNT, pboIds);   glBindBufferARB(GL_PIXEL_PACK_BUFFER_ARB, pboIds[0]);   glBufferDataARB(GL_PIXEL_PACK_BUFFER_ARB, DATA_SIZE, 0, GL_STREAM_READ_ARB);   glBindBufferARB(GL_PIXEL_PACK_BUFFER_ARB, pboIds[1]);   glBufferDataARB(GL_PIXEL_PACK_BUFFER_ARB, DATA_SIZE, 0, GL_STREAM_READ_ARB);   glBindBufferARB(GL_PIXEL_PACK_BUFFER_ARB, 0);    }glShadeModel(GL_SMOOTH);// Enable Smooth ShadingglClearColor(0.0f, 0.0f, 0.0f, 0.5f);// Black BackgroundglClearDepth(1.0f);// Depth Buffer SetupglEnable(GL_DEPTH_TEST);// Enables Depth TestingglDepthFunc(GL_LEQUAL);// The Type Of Depth Testing To DoglHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST);// Really Nice Perspective Calculationsreturn TRUE;// Initialization Went OK}///////////////////////////////////////////////////////////////////////////////// change the brightness///////////////////////////////////////////////////////////////////////////////void add(unsigned char* src, int width, int height, int shift, unsigned char* dst){    if(!src || !dst)   return;    int value;    for(int i = 0; i < height; ++i)    {   for(int j = 0; j < width; ++j)   {  value = *src + shift;  if(value > 255) *dst = (unsigned char)255;  else  *dst = (unsigned char)value;  ++src;  ++dst;  value = *src + shift;  if(value > 255) *dst = (unsigned char)255;  else  *dst = (unsigned char)value;  ++src;  ++dst;  value = *src + shift;  if(value > 255) *dst = (unsigned char)255;  else  *dst = (unsigned char)value;  ++src;  ++dst;  ++src;    // skip alpha  ++dst;   }    }}///////////////////////////////////////////////////////////////////////////////// draw a cube with immediate mode// 54 calls = 24 glVertex*() calls + 24 glColor*() calls + 6 glNormal*() calls///////////////////////////////////////////////////////////////////////////////void draw(){    glBegin(GL_QUADS);   // face v0-v1-v2-v3   glNormal3f(0,0,1);   glColor3f(1,1,1);   glVertex3f(1,1,1);   glColor3f(1,1,0);   glVertex3f(-1,1,1);   glColor3f(1,0,0);   glVertex3f(-1,-1,1);   glColor3f(1,0,1);   glVertex3f(1,-1,1);   // face v0-v3-v4-v6   glNormal3f(1,0,0);   glColor3f(1,1,1);   glVertex3f(1,1,1);   glColor3f(1,0,1);   glVertex3f(1,-1,1);   glColor3f(0,0,1);   glVertex3f(1,-1,-1);   glColor3f(0,1,1);   glVertex3f(1,1,-1);   // face v0-v5-v6-v1   glNormal3f(0,1,0);   glColor3f(1,1,1);   glVertex3f(1,1,1);   glColor3f(0,1,1);   glVertex3f(1,1,-1);   glColor3f(0,1,0);   glVertex3f(-1,1,-1);   glColor3f(1,1,0);   glVertex3f(-1,1,1);   // face  v1-v6-v7-v2   glNormal3f(-1,0,0);   glColor3f(1,1,0);   glVertex3f(-1,1,1);   glColor3f(0,1,0);   glVertex3f(-1,1,-1);   glColor3f(0,0,0);   glVertex3f(-1,-1,-1);   glColor3f(1,0,0);   glVertex3f(-1,-1,1);   // face v7-v4-v3-v2   glNormal3f(0,-1,0);   glColor3f(0,0,0);   glVertex3f(-1,-1,-1);   glColor3f(0,0,1);   glVertex3f(1,-1,-1);   glColor3f(1,0,1);   glVertex3f(1,-1,1);   glColor3f(1,0,0);   glVertex3f(-1,-1,1);   // face v4-v7-v6-v5   glNormal3f(0,0,-1);   glColor3f(0,0,1);   glVertex3f(1,-1,-1);   glColor3f(0,0,0);   glVertex3f(-1,-1,-1);   glColor3f(0,1,0);   glVertex3f(-1,1,-1);   glColor3f(0,1,1);   glVertex3f(1,1,-1);    glEnd();}void toOrtho(){    // set viewport to be the entire window    glViewport((GLsizei)SCREEN_WIDTH, 0, (GLsizei)SCREEN_WIDTH, (GLsizei)SCREEN_HEIGHT);    // set orthographic viewing frustum    glMatrixMode(GL_PROJECTION);    glLoadIdentity();    glOrtho(0, SCREEN_WIDTH, 0, SCREEN_HEIGHT, -1, 1);    // switch to modelview matrix in order to set scene    glMatrixMode(GL_MODELVIEW);    glLoadIdentity();    gluLookAt(0, 0, 0, 0, 0, -1, 0, 1, 0); // eye(x,y,z), focal(x,y,z), up(x,y,z)}void toPerspective(){    // set viewport to be the entire window    glViewport(0, 0, (GLsizei)SCREEN_WIDTH, (GLsizei)SCREEN_HEIGHT);    // set perspective viewing frustum    glMatrixMode(GL_PROJECTION);    glLoadIdentity();    gluPerspective(60.0f, (float)(SCREEN_WIDTH)/SCREEN_HEIGHT, 1.0f, 1000.0f); // FOV, AspectRatio, NearClip, FarClip    // switch to modelview matrix in order to set scene    glMatrixMode(GL_MODELVIEW);    glLoadIdentity();    gluLookAt(0, 0, 8, 0, 0, 0, 0, 1, 0); // eye(x,y,z), focal(x,y,z), up(x,y,z)}int DrawLesson5Scene(GLvoid)// Here's Where We Do All The Drawing{//glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);// Clear Screen And Depth Buffer//glLoadIdentity();// Reset The Current Modelview MatrixglTranslatef(-1.5f,0.0f,-6.0f);// Move Left 1.5 Units And Into The Screen 6.0glRotatef(rtri,0.0f,1.0f,0.0f);// Rotate The Triangle On The Y axis ( NEW )glBegin(GL_TRIANGLES);// Start Drawing A TriangleglColor3f(1.0f,0.0f,0.0f);// RedglVertex3f( 0.0f, 1.0f, 0.0f);// Top Of Triangle (Front)glColor3f(0.0f,1.0f,0.0f);// GreenglVertex3f(-1.0f,-1.0f, 1.0f);// Left Of Triangle (Front)glColor3f(0.0f,0.0f,1.0f);// BlueglVertex3f( 1.0f,-1.0f, 1.0f);// Right Of Triangle (Front)glColor3f(1.0f,0.0f,0.0f);// RedglVertex3f( 0.0f, 1.0f, 0.0f);// Top Of Triangle (Right)glColor3f(0.0f,0.0f,1.0f);// BlueglVertex3f( 1.0f,-1.0f, 1.0f);// Left Of Triangle (Right)glColor3f(0.0f,1.0f,0.0f);// GreenglVertex3f( 1.0f,-1.0f, -1.0f);// Right Of Triangle (Right)glColor3f(1.0f,0.0f,0.0f);// RedglVertex3f( 0.0f, 1.0f, 0.0f);// Top Of Triangle (Back)glColor3f(0.0f,1.0f,0.0f);// GreenglVertex3f( 1.0f,-1.0f, -1.0f);// Left Of Triangle (Back)glColor3f(0.0f,0.0f,1.0f);// BlueglVertex3f(-1.0f,-1.0f, -1.0f);// Right Of Triangle (Back)glColor3f(1.0f,0.0f,0.0f);// RedglVertex3f( 0.0f, 1.0f, 0.0f);// Top Of Triangle (Left)glColor3f(0.0f,0.0f,1.0f);// BlueglVertex3f(-1.0f,-1.0f,-1.0f);// Left Of Triangle (Left)glColor3f(0.0f,1.0f,0.0f);// GreenglVertex3f(-1.0f,-1.0f, 1.0f);// Right Of Triangle (Left)glEnd();// Done Drawing The PyramidglLoadIdentity();// Reset The Current Modelview MatrixglTranslatef(1.5f,0.0f,-7.0f);// Move Right 1.5 Units And Into The Screen 7.0glRotatef(rquad,1.0f,1.0f,1.0f);// Rotate The Quad On The X axis ( NEW )glBegin(GL_QUADS);// Draw A QuadglColor3f(0.0f,1.0f,0.0f);// Set The Color To BlueglVertex3f( 1.0f, 1.0f,-1.0f);// Top Right Of The Quad (Top)glVertex3f(-1.0f, 1.0f,-1.0f);// Top Left Of The Quad (Top)glVertex3f(-1.0f, 1.0f, 1.0f);// Bottom Left Of The Quad (Top)glVertex3f( 1.0f, 1.0f, 1.0f);// Bottom Right Of The Quad (Top)glColor3f(1.0f,0.5f,0.0f);// Set The Color To OrangeglVertex3f( 1.0f,-1.0f, 1.0f);// Top Right Of The Quad (Bottom)glVertex3f(-1.0f,-1.0f, 1.0f);// Top Left Of The Quad (Bottom)glVertex3f(-1.0f,-1.0f,-1.0f);// Bottom Left Of The Quad (Bottom)glVertex3f( 1.0f,-1.0f,-1.0f);// Bottom Right Of The Quad (Bottom)glColor3f(1.0f,0.0f,0.0f);// Set The Color To RedglVertex3f( 1.0f, 1.0f, 1.0f);// Top Right Of The Quad (Front)glVertex3f(-1.0f, 1.0f, 1.0f);// Top Left Of The Quad (Front)glVertex3f(-1.0f,-1.0f, 1.0f);// Bottom Left Of The Quad (Front)glVertex3f( 1.0f,-1.0f, 1.0f);// Bottom Right Of The Quad (Front)glColor3f(1.0f,1.0f,0.0f);// Set The Color To YellowglVertex3f( 1.0f,-1.0f,-1.0f);// Top Right Of The Quad (Back)glVertex3f(-1.0f,-1.0f,-1.0f);// Top Left Of The Quad (Back)glVertex3f(-1.0f, 1.0f,-1.0f);// Bottom Left Of The Quad (Back)glVertex3f( 1.0f, 1.0f,-1.0f);// Bottom Right Of The Quad (Back)glColor3f(0.0f,0.0f,1.0f);// Set The Color To BlueglVertex3f(-1.0f, 1.0f, 1.0f);// Top Right Of The Quad (Left)glVertex3f(-1.0f, 1.0f,-1.0f);// Top Left Of The Quad (Left)glVertex3f(-1.0f,-1.0f,-1.0f);// Bottom Left Of The Quad (Left)glVertex3f(-1.0f,-1.0f, 1.0f);// Bottom Right Of The Quad (Left)glColor3f(1.0f,0.0f,1.0f);// Set The Color To VioletglVertex3f( 1.0f, 1.0f,-1.0f);// Top Right Of The Quad (Right)glVertex3f( 1.0f, 1.0f, 1.0f);// Top Left Of The Quad (Right)glVertex3f( 1.0f,-1.0f, 1.0f);// Bottom Left Of The Quad (Right)glVertex3f( 1.0f,-1.0f,-1.0f);// Bottom Right Of The Quad (Right)glEnd();// Done Drawing The Quadrtri+=0.2f;// Increase The Rotation Variable For The Triangle ( NEW )rquad-=0.15f;// Decrease The Rotation Variable For The Quad ( NEW )return TRUE;// Keep Going}int DrawGLScene(GLvoid)// Here's Where We Do All The Drawing{static int shift = 0;    static int index = 0;    int nextIndex = 0;   // pbo index used for next frame    // brightness shift amount    shift = ++shift % 200;    // increment current index first then get the next index    // "index" is used to read pixels from a framebuffer to a PBO    // "nextIndex" is used to process pixels in the other PBO    index = (index + 1) % 2;    nextIndex = (index + 1) % 2;// set the framebuffer to read    glReadBuffer(GL_FRONT);    if(pboUsed) // with PBO    {   // read framebuffer ///////////////////////////////    timer.start();    // copy pixels from framebuffer to PBO   // Use offset instead of ponter.   // OpenGL should perform asynch DMA transfer, so glReadPixels() will return immediately.   glBindBufferARB(GL_PIXEL_PACK_BUFFER_ARB, pboIds[index]);   glReadPixels(0, 0, SCREEN_WIDTH, SCREEN_HEIGHT, PIXEL_FORMAT, GL_UNSIGNED_BYTE, 0);// measure the time reading framebuffer   timer.stop();   readTime = timer.getElapsedTimeInMilliSec();   ///////////////////////////////////////////////////   // process pixel data /////////////////////////////   // map the PBO that contain framebuffer pixels before processing it   glBindBufferARB(GL_PIXEL_PACK_BUFFER_ARB, pboIds[nextIndex]);   GLubyte* src = (GLubyte*)glMapBufferARB(GL_PIXEL_PACK_BUFFER_ARB, GL_READ_ONLY_ARB);   if(src)   {  // change brightness  add(src, SCREEN_WIDTH, SCREEN_HEIGHT, shift, colorBuffer);  glUnmapBufferARB(GL_PIXEL_PACK_BUFFER_ARB);// release pointer to the mapped buffer   }    glBindBufferARB(GL_PIXEL_PACK_BUFFER_ARB, 0);    } else   // without PBO    { // read framebuffer ///////////////////////////////   timer.start();   // read framebuffer ///////////////////////////////  glReadPixels(0, 0, SCREEN_WIDTH, SCREEN_HEIGHT, PIXEL_FORMAT, GL_UNSIGNED_BYTE, colorBuffer);   // measure the time reading framebuffer   timer.stop();   readTime = timer.getElapsedTimeInMilliSec();   ///////////////////////////////////////////////////    // change brightness   add(colorBuffer, SCREEN_WIDTH, SCREEN_HEIGHT, shift, colorBuffer);    }  // render to the framebuffer //////////////////////////    glDrawBuffer(GL_BACK); toPerspective(); // set to perspective on the left side of the window // clear buffer    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);    ////// tramsform camera    //glTranslatef(0, 0, cameraDistance);    //glRotatef(cameraAngleX, 1, 0, 0);   // pitch    //glRotatef(cameraAngleY, 0, 1, 0);   // heading    //// draw a cube    //draw();DrawLesson5Scene();    // draw the read color buffer to the right side of the window    toOrtho(); // set to orthographic on the right side of the window    glRasterPos2i(0, 0);    glDrawPixels(SCREEN_WIDTH, SCREEN_HEIGHT, PIXEL_FORMAT, GL_UNSIGNED_BYTE, colorBuffer);// draw info messages    showInfo();    printTransferRate();//glutSwapBuffers();return TRUE;// Keep Going}GLvoid KillGLWindow(GLvoid)// Properly Kill The Window{if (fullscreen)// Are We In Fullscreen Mode?{ChangeDisplaySettings(NULL,0);// If So Switch Back To The DesktopShowCursor(TRUE);// Show Mouse Pointer}if (hRC)// Do We Have A Rendering Context?{if (!wglMakeCurrent(NULL,NULL))// Are We Able To Release The DC And RC Contexts?{MessageBox(NULL,"Release Of DC And RC Failed.","SHUTDOWN ERROR",MB_OK | MB_ICONINFORMATION);}if (!wglDeleteContext(hRC))// Are We Able To Delete The RC?{MessageBox(NULL,"Release Rendering Context Failed.","SHUTDOWN ERROR",MB_OK | MB_ICONINFORMATION);}hRC=NULL;// Set RC To NULL}if (hDC && !ReleaseDC(hWnd,hDC))// Are We Able To Release The DC{MessageBox(NULL,"Release Device Context Failed.","SHUTDOWN ERROR",MB_OK | MB_ICONINFORMATION);hDC=NULL;// Set DC To NULL}if (hWnd && !DestroyWindow(hWnd))// Are We Able To Destroy The Window?{MessageBox(NULL,"Could Not Release hWnd.","SHUTDOWN ERROR",MB_OK | MB_ICONINFORMATION);hWnd=NULL;// Set hWnd To NULL}if (!UnregisterClass("OpenGL",hInstance))// Are We Able To Unregister Class{MessageBox(NULL,"Could Not Unregister Class.","SHUTDOWN ERROR",MB_OK | MB_ICONINFORMATION);hInstance=NULL;// Set hInstance To NULL}}/*This Code Creates Our OpenGL Window.  Parameters Are:* *title- Title To Appear At The Top Of The Window* *width- Width Of The GL Window Or Fullscreen Mode* *height- Height Of The GL Window Or Fullscreen Mode* *bits- Number Of Bits To Use For Color (8/16/24/32)* *fullscreenflag- Use Fullscreen Mode (TRUE) Or Windowed Mode (FALSE)*/ BOOL CreateGLWindow(char* title, int width, int height, int bits, bool fullscreenflag){GLuintPixelFormat;// Holds The Results After Searching For A MatchWNDCLASSwc;// Windows Class StructureDWORDdwExstyle;// Window Extended styleDWORDdwstyle;// Window styleRECTWindowRect;// Grabs Rectangle Upper Left / Lower Right ValuesWindowRect.left=(long)0;// Set Left Value To 0WindowRect.right=(long)width;// Set Right Value To Requested WidthWindowRect.top=(long)0;// Set Top Value To 0WindowRect.bottom=(long)height;// Set Bottom Value To Requested Heightfullscreen=fullscreenflag;// Set The Global Fullscreen FlaghInstance= GetModuleHandle(NULL);// Grab An Instance For Our Windowwc.style= CS_HREDRAW | CS_VREDRAW | CS_OWNDC;// Redraw On Size, And Own DC For Window.wc.lpfnWndProc= (WNDPROC) WndProc;// WndProc Handles Messageswc.cbClsExtra= 0;// No Extra Window Datawc.cbWndExtra= 0;// No Extra Window Datawc.hInstance= hInstance;// Set The Instancewc.hIcon= LoadIcon(NULL, IDI_WINLOGO);// Load The Default Iconwc.hCursor= LoadCursor(NULL, IDC_ARROW);// Load The Arrow Pointerwc.hbrBackground= NULL;// No Background Required For GLwc.lpszMenuName= NULL;// We Don't Want A Menuwc.lpszClassName= "OpenGL";// Set The Class Nameif (!RegisterClass(&wc))// Attempt To Register The Window Class{MessageBox(NULL,"Failed To Register The Window Class.","ERROR",MB_OK|MB_ICONEXCLAMATION);return FALSE;// Return FALSE} if (fullscreen)// Attempt Fullscreen Mode?{DEVMODE dmScreenSettings;// Device Modememset(&dmScreenSettings,0,sizeof(dmScreenSettings));// Makes Sure Memory's CleareddmScreenSettings.dmSize=sizeof(dmScreenSettings);// Size Of The Devmode StructuredmScreenSettings.dmPelsWidth= width;// Selected Screen WidthdmScreenSettings.dmPelsHeight= height;// Selected Screen HeightdmScreenSettings.dmBitsPerPel= bits;// Selected Bits Per PixeldmScreenSettings.dmFields=DM_BITSPERPEL|DM_PELSWIDTH|DM_PELSHEIGHT;// Try To Set Selected Mode And Get Results.  NOTE: CDS_FULLSCREEN Gets Rid Of Start Bar.if (ChangeDisplaySettings(&dmScreenSettings,CDS_FULLSCREEN)!=DISP_CHANGE_SUCCESSFUL){// If The Mode Fails, Offer Two Options.  Quit Or Use Windowed Mode.if (MessageBox(NULL,"The Requested Fullscreen Mode Is Not Supported By\nYour Video Card. Use Windowed Mode Instead?","NeHe GL",MB_YESNO|MB_ICONEXCLAMATION)==IDYES){fullscreen=FALSE;// Windowed Mode Selected.  Fullscreen = FALSE}else{// Pop Up A Message Box Letting User Know The Program Is Closing.MessageBox(NULL,"Program Will Now Close.","ERROR",MB_OK|MB_ICONSTOP);return FALSE;// Return FALSE}}}if (fullscreen)// Are We Still In Fullscreen Mode?{dwExstyle=WS_EX_APPWINDOW;// Window Extended styledwstyle=WS_POPUP;// Windows styleShowCursor(FALSE);// Hide Mouse Pointer}else{dwExstyle=WS_EX_APPWINDOW | WS_EX_WINDOWEDGE;// Window Extended styledwstyle=WS_OVERLAPPEDWINDOW;// Windows style}AdjustWindowRectEx(&WindowRect, dwstyle, FALSE, dwExstyle);// Adjust Window To True Requested Size// Create The Windowif (!(hWnd=CreateWindowEx(dwExstyle,// Extended style For The Window"OpenGL",// Class Nametitle,// Window Titledwstyle |// Defined Window styleWS_CLIPSIBLINGS |// Required Window styleWS_CLIPCHILDREN,// Required Window style0, 0,// Window PositionWindowRect.right-WindowRect.left,// Calculate Window WidthWindowRect.bottom-WindowRect.top,// Calculate Window HeightNULL,// No Parent WindowNULL,// No MenuhInstance,// InstanceNULL)))// Dont Pass Anything To WM_CREATE{KillGLWindow();// Reset The DisplayMessageBox(NULL,"Window Creation Error.","ERROR",MB_OK|MB_ICONEXCLAMATION);return FALSE;// Return FALSE}staticPIXELFORMATDESCRIPTOR pfd=// pfd Tells Windows How We Want Things To Be{sizeof(PIXELFORMATDESCRIPTOR),// Size Of This Pixel Format Descriptor1,// Version NumberPFD_DRAW_TO_WINDOW |// Format Must Support WindowPFD_SUPPORT_OPENGL |// Format Must Support OpenGLPFD_DOUBLEBUFFER,// Must Support Double BufferingPFD_TYPE_RGBA,// Request An RGBA Formatbits,// Select Our Color Depth8, 0, 8, 0, 8, 0,// Color Bits Ignored8,// No Alpha Buffer0,// Shift Bit Ignored0,// No Accumulation Buffer0, 0, 0, 0,// Accumulation Bits Ignored16,// 16Bit Z-Buffer (Depth Buffer)  0,// No Stencil Buffer0,// No Auxiliary BufferPFD_MAIN_PLANE,// Main Drawing Layer0,// Reserved0, 0, 0// Layer Masks Ignored//sizeof(PIXELFORMATDESCRIPTOR),// Size Of This Pixel Format Descriptor//1,// Version Number//PFD_DRAW_TO_WINDOW |// Format Must Support Window//PFD_SUPPORT_OPENGL |// Format Must Support OpenGL//PFD_DOUBLEBUFFER,// Must Support Double Buffering//PFD_TYPE_RGBA,// Request An RGBA Format//bits,// Select Our Color Depth//0, 0, 0, 0, 0, 0,// Color Bits Ignored//0,// No Alpha Buffer//0,// Shift Bit Ignored//0,// No Accumulation Buffer//0, 0, 0, 0,// Accumulation Bits Ignored//16,// 16Bit Z-Buffer (Depth Buffer)  //0,// No Stencil Buffer//0,// No Auxiliary Buffer//PFD_MAIN_PLANE,// Main Drawing Layer//0,// Reserved//0, 0, 0}; if (!(hDC=GetDC(hWnd)))// Did We Get A Device Context?{KillGLWindow();// Reset The DisplayMessageBox(NULL,"Can't Create A GL Device Context.","ERROR",MB_OK|MB_ICONEXCLAMATION);return FALSE;// Return FALSE}if (!(PixelFormat=ChoosePixelFormat(hDC,&pfd)))// Did Windows Find A Matching Pixel Format?{KillGLWindow();// Reset The DisplayMessageBox(NULL,"Can't Find A Suitable PixelFormat.","ERROR",MB_OK|MB_ICONEXCLAMATION);return FALSE;// Return FALSE}if(!SetPixelFormat(hDC,PixelFormat,&pfd))// Are We Able To Set The Pixel Format?{KillGLWindow();// Reset The DisplayMessageBox(NULL,"Can't Set The PixelFormat.","ERROR",MB_OK|MB_ICONEXCLAMATION);return FALSE;// Return FALSE}if (!(hRC=wglCreateContext(hDC)))// Are We Able To Get A Rendering Context?{KillGLWindow();// Reset The DisplayMessageBox(NULL,"Can't Create A GL Rendering Context.","ERROR",MB_OK|MB_ICONEXCLAMATION);return FALSE;// Return FALSE}if(!wglMakeCurrent(hDC,hRC))// Try To Activate The Rendering Context{KillGLWindow();// Reset The DisplayMessageBox(NULL,"Can't Activate The GL Rendering Context.","ERROR",MB_OK|MB_ICONEXCLAMATION);return FALSE;// Return FALSE}ShowWindow(hWnd,SW_SHOW);// Show The WindowSetForegroundWindow(hWnd);// Slightly Higher PrioritySetFocus(hWnd);// Sets Keyboard Focus To The WindowReSizeGLScene(width, height);// Set Up Our Perspective GL Screenif (!InitGL())// Initialize Our Newly Created GL Window{KillGLWindow();// Reset The DisplayMessageBox(NULL,"Initialization Failed.","ERROR",MB_OK|MB_ICONEXCLAMATION);return FALSE;// Return FALSE}return TRUE;// Success}LRESULT CALLBACK WndProc(HWNDhWnd,// Handle For This WindowUINTuMsg,// Message For This WindowWPARAMwParam,// Additional Message InformationLPARAMlParam)// Additional Message Information{switch (uMsg)// Check For Windows Messages{case WM_ACTIVATE:// Watch For Window Activate Message{if (!HIWORD(wParam))// Check Minimization State{active=TRUE;// Program Is Active}else{active=FALSE;// Program Is No Longer Active}return 0;// Return To The Message Loop}case WM_SYSCOMMAND:// Intercept System Commands{switch (wParam)// Check System Calls{case SC_SCREENSAVE:// Screensaver Trying To Start?case SC_MONITORPOWER:// Monitor Trying To Enter Powersave?return 0;// Prevent From Happening}break;// Exit}case WM_CLOSE:// Did We Receive A Close Message?{PostQuitMessage(0);// Send A Quit Messagereturn 0;// Jump Back}case WM_KEYDOWN:// Is A Key Being Held Down?{keys[wParam] = TRUE;// If So, Mark It As TRUEreturn 0;// Jump Back}case WM_KEYUP:// Has A Key Been Released?{keys[wParam] = FALSE;// If So, Mark It As FALSEreturn 0;// Jump Back}case WM_SIZE:// Resize The OpenGL Window{ReSizeGLScene(LOWORD(lParam),HIWORD(lParam));  // LoWord=Width, HiWord=Heightreturn 0;// Jump Back}}// Pass All Unhandled Messages To DefWindowProcreturn DefWindowProc(hWnd,uMsg,wParam,lParam);}///////////////////////////////////////////////////////////////////////////////// initialize GLUT for windowing///////////////////////////////////////////////////////////////////////////////int initGLUT(int argc, char **argv){    // GLUT stuff for windowing    // initialization openGL window.    // it is called before any other GLUT routine    glutInit(&argc, argv);    glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_ALPHA); // display mode    glutInitWindowSize(SCREEN_WIDTH*2, SCREEN_HEIGHT);    // window size    glutInitWindowPosition(100, 100); // window location    // finally, create a window with openGL context    // Window will not displayed until glutMainLoop() is called    // it returns a unique ID    int handle = glutCreateWindow(argv[0]);// param is the title of window    // register GLUT callback functions    //glutDisplayFunc(DrawGLScene);    //glutTimerFunc(33, timerCB, 33);   // redraw only every given millisec    glutIdleFunc(idleCB);   // redraw only every given millisec    //glutReshapeFunc(reshapeCB);    //glutKeyboardFunc(keyboardCB);    //glutMouseFunc(mouseCB);    //glutMotionFunc(mouseMotionCB);    return handle;}int WINAPI WinMain(HINSTANCEhInstance,// InstanceHINSTANCEhPrevInstance,// Previous InstanceLPSTRlpCmdLine,// Command Line ParametersintnCmdShow)// Window Show State/////////////////////////////////////////////////////////////////////////////////int main(int argc, char **argv){// init GLUT and GL    //initGLUT(argc, argv);    //initGL();InitGL(); //// the last GLUT call (LOOP) //   // window will be shown and display callback is triggered by events //   // NOTE: this call never return main(). //   glutMainLoop(); /* Start GLUT event-processing loop */ MSGmsg;// Windows Message StructureBOOLdone=FALSE;// Bool Variable To Exit Loop// Ask The User Which Screen Mode They Preferif (MessageBox(NULL,"Would You Like To Run In Fullscreen Mode?", "Start FullScreen?",MB_YESNO|MB_ICONQUESTION)==IDNO){fullscreen=FALSE;// Windowed Mode} // Create Our OpenGL Windowif (!CreateGLWindow("NeHe's Solid Object Tutorial",512,256,32,fullscreen)){return 0;// Quit If Window Was Not Created}while(!done)// Loop That Runs While done=FALSE{if (PeekMessage(&msg,NULL,0,0,PM_REMOVE))// Is There A Message Waiting?{if (msg.message==WM_QUIT)// Have We Received A Quit Message?{done=TRUE;// If So done=TRUE}else// If Not, Deal With Window Messages{TranslateMessage(&msg;// Translate The MessageDispatchMessage(&msg;// Dispatch The Message}}else// If There Are No Messages{// Draw The Scene.  Watch For ESC Key And Quit Messages From DrawGLScene()if ((active && !DrawGLScene()) || keys[VK_ESCAPE])// Active?  Was There A Quit Received?{done=TRUE;// ESC or DrawGLScene Signalled A Quit}else// Not Time To Quit, Update Screen{SwapBuffers(hDC);// Swap Buffers (Double Buffering)}if (keys[VK_F1])// Is F1 Being Pressed?{keys[VK_F1]=FALSE;// If So Make Key FALSEKillGLWindow();// Kill Our Current Windowfullscreen=!fullscreen;// Toggle Fullscreen / Windowed Mode// Recreate Our OpenGL Windowif (!CreateGLWindow("NeHe's Solid Object Tutorial",512,256,32,fullscreen)){return 0;// Quit If Window Was Not Created}}}}// ShutdownKillGLWindow();// Kill The Windowreturn (msg.wParam);// Exit The Program//return 0;}void reshapeCB(int w, int h){    toPerspective();}void timerCB(int millisec){    glutTimerFunc(millisec, timerCB, millisec);    glutPostRedisplay();}void idleCB(){    glutPostRedisplay();}void keyboardCB(unsigned char key, int x, int y){    switch(key)    {    case 27: // ESCAPE   clearSharedMem();   //exit(0);   break;    case ' ':   if(pboSupported)  pboUsed = !pboUsed;   cout << "PBO mode: " << (pboUsed ? "on" : "off") << endl;    break;    case 'd': // switch rendering modes (fill -> wire -> point)    case 'D':   drawMode = ++drawMode % 3;   if(drawMode == 0)   // fill mode   {  glPolygonMode(GL_FRONT_AND_BACK, GL_FILL);  glEnable(GL_DEPTH_TEST);  glEnable(GL_CULL_FACE);   }   else if(drawMode == 1)  // wireframe mode   {  glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);  glDisable(GL_DEPTH_TEST);  glDisable(GL_CULL_FACE);   }   else// point mode   {  glPolygonMode(GL_FRONT_AND_BACK, GL_POINT);  glDisable(GL_DEPTH_TEST);  glDisable(GL_CULL_FACE);   }   break;    default:   ;    }    glutPostRedisplay();}void mouseCB(int button, int state, int x, int y){    mouseX = x;    mouseY = y;    if(button == GLUT_LEFT_BUTTON)    {   if(state == GLUT_DOWN)   {  mouseLeftDown = true;   }   else if(state == GLUT_UP)  mouseLeftDown = false;    }    else if(button == GLUT_RIGHT_BUTTON)    {   if(state == GLUT_DOWN)   {  mouseRightDown = true;   }   else if(state == GLUT_UP)  mouseRightDown = false;    }}void mouseMotionCB(int x, int y){    if(mouseLeftDown)    {   cameraAngleY += (x - mouseX);   cameraAngleX += (y - mouseY);   mouseX = x;   mouseY = y;    }    if(mouseRightDown)    {   cameraDistance += (y - mouseY) * 0.2f;   mouseY = y;    }}===============================================================================The primary difference between all these three technique is the way the windows of the application are created.I want to achieve the same speed performance on SDL application. Any help in this regard will be highly appreciated. Eagerly waiting for your early response.
  That's A LOT of code for even the most insane person to go through...What was wrong with the code again?   ;  First of all thanks for your reply. I just want to know that what values do I need to initialize in SDL before creating a SDL window in order to get PBO to work. Currently I am using the following lines of code to bring SDL window. But when I use PBO it does not have any performance benefits as was with when I create window using GLUT or plain Windows programming using WinMain./*--------------------------------------------------* Setup SDL*--------------------------------------------------*/bool init_SDL(){//Init all SDL Partsif(SDL_Init(SDL_INIT_EVERYTHING) == -1){return false;}//screen = SDL_SetVideoMode( SCREEN_WIDTH, SCREEN_HEIGHT, SCREEN_BPP, SDL_OPENGL | SDL_DOUBLEBUF | SDL_FULLSCREEN ); //FULLSCREENscreen = SDL_SetVideoMode( SCREEN_WIDTH*2, SCREEN_HEIGHT, SCREEN_BPP, SDL_OPENGL | SDL_DOUBLEBUF);SDL_WM_SetCaption("Simple SDL Demo", NULL);return true;}Is there any way to change the pixelformatdescriptor of SDL? or some other better way to get results. Eagerly waiting for your reply. Thanks.   ;  I am unsure about the specifics of PBO, but it *might* help if you add SDL_HWSURFACE | SDL_OPENGL. As far as I know the SDL_HWSURFACE would direct SDL to use hardware acceleration on the screen.Why aren't you happy with GLUT alone then? IMO if it works for your purpose then stick with it. I personally cannot see any advantages of using SDL over GLUT except for maybe cross-platforming (Which GLUT already does).Hope that helps. =)   ;  Flags like SDL_DOUBLEBUF and SDL_HWSURFACE have no effect on an OpenGL rendering context. Also, you don't define the bit depth in SDL_SetVideoMode for OpenGL, just pass 0. The only flag you need is SDL_OPENGL and optionally SDL_FULLSCREEN if you want fullscreen. You configure other things like bit depth, double buffering, etc with SDL_GL_SetAttribute (which you must call before SDL_SetVideoMode). To create an OpenGL rendering context with SDL, the correct order of calls is:SDL_Init(SDL_INIT_VIDEO);//setup OpenGL parametersSDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);SDL_GL_SetAttribute( SDL_GL_RED_SIZE, 8 );SDL_GL_SetAttribute( SDL_GL_GREEN_SIZE, 8 );SDL_GL_SetAttribute( SDL_GL_BLUE_SIZE, 8 );SDL_GL_SetAttribute( SDL_GL_ALPHA_SIZE, 8 );SDL_GL_SetAttribute( SDL_GL_DEPTH_SIZE, 0 );//and so on, set other attributes hereSDL_SetVideoMode(SCREEN_WIDTH, SCREEN_HEIGHT, 0, SDL_OPENGL);You can read more here.Once you have a valid OpenGL rendering context, then you can use OpenGL features such as PBO. Since you never actually define your rendering context correctly, my guess is the speed difference is due to OpenGL having to convert from whatever the default format is to match the format of the PBO. Thus the performance hit. Use SDL_GL_SetAttribute properly to make your framebuffer format match your PBO format and I bet you will see a big improvement in performance.   ;  First of all thanks for your kind reply. I have tried what you said and it resolves my issue, the glReadPixels now takes only 0-1 ms. But unfortunately by setting the rendering context, the frame rate of the rest of the scene suddenly drops by a factor of 5 like previously it was 42 and now it is showing maximum frame rate of 34. So what should I do next to resolve it. Are there any other setting besides the parameters that you have shown. Eagerly waiting for your early response. Thanks.   ;  I'm glad that you resolved your initial issue. As for the drop in frame rate, I will admit that I have not reviewed your code in depth, so I can not make a direct recommendation. On one hand, I probably would not worry about a drop of 5 frames per second. On the other hand, your code does not appear to be doing anything terribly complex, so it is strange to see a drop. Did you benchmark your updated code with the GLUT version? What type of GPU are you running this on?   ;  Thanks for your reply. In fact the code that I have posted earlier is only a sample code that I have used for illustration of my previous issue. I am in fact running a game that includes sea environment, terrain and some harbors area. And by defining the openGL rendering context parameters for SDL it drops to 34 FPS maximum and this causes the scene to jerk at some time due to sea rendering. But if I run the code without defining the openGL context parameters for SDL it gives FPS of 40 maximum. The GPU that I have is nVidia 8500 GT. But I think that it does not have any effect on it because I have also run this code in my office where it is showing the similar behavior where I have nVidia 8800 GTS. Waiting for your reply. Thanks.   