   Help with vertical flipping
  Hello Everyone,  I am new to this forum and new to OpenGL...  You help is very much appreciated..I am currently obtaining video pixel information from a webcam and plotting them on a openGL window but the display is inverted.To display the pixels i am using glDrawPixels(w,h,GL_BGRA,GL_UNSIGNED_BYTE,buffer);updateGL();the above code displays my video frames but is inverted. If i add glPixelZoom(1.0f, -1.0f); before glDrawPixles to invert the display the display goes blank... please help...thankx in advancevasanth   
  Using glPixelZoom(1.0f, -1.0f) is correct, however, since your origin is (0,0), which is the lower left of your screen, the image is now entirely off the screen. You'll need to set the raster position to the upper left (i.e. (0, 480)) before you render. I suggest using glWindowPos instead of glRasterPos, as glWindowPos does not go through the matrix transform like glRasterPos does.glWindowPos is/was an extension and I'm not sure if it has been pulled into the core as of 1.5 or so (on Windows you'll have to wglProcAddress() it no matter what).   ;  thanx for the replyi am now using glPixelZoom(1.0f, -1.0f);glRasterPos2f(-1,1.0);glDrawPixels(w,h,GL_BGRA,GL_UNSIGNED_BYTE,c1.buffer);this does flip the image and displays it right but the top 25% is still blank and glRasterPos2f seems to take values only from -1 to +1 .. please advicevasanth   ;  The call to glRasterPos transform the point you supply by the current modelview and projection matrix.To make glRasterPos == glWindowPos, just do the following:glMatrixMode(GL_PROJECTION);glLoadIdentity();glOrtho(0, WindowWidth, 0, WindowHeight, -1, 1);glMatrixMdoe(GL_MODELVIEW);glLoadIdentity();glRasterPos2f(0, WindowHeight);Then you should be good to go. The rasterpos stuff is kind of overdone for my tastes (which is why I tend to prefer glWindowPos). Just play with it a bit and you'll see.;  when i do this glMatrixMode(GL_PROJECTION);glLoadIdentity();glOrtho(0 ,width(), 0, height(), -1, 1);glMatrixMode(GL_MODELVIEW);glLoadIdentity();glRasterPos2i(0,height());glPixelZoom(1.0f, -1.0f);glDrawPixels(c1.getWidth(),c1.getHeight(),GL_BGRA,GL_UNSIGNED_BYTE,c1.getBuffer());I get a blank screen but if I change it to  glRasterPos2i(0,height()-1);  I get the display but the top 33% (aprox) is still blank..  its like the image needs to be moved up a bit..  Sorry to sound like a noob.. i ahve never worked with openGL and I just need to get this working before I proceed to other parts whih has nothing to do with openGLthanx in advancevasanth   