text: /*
   * 3-D gear wheels.  This program is in the public domain.
   *
   * Command line options:
   *    -info      print GL implementation information
   *    -exit      automatically exit after 30 seconds
   *
   *
   * Brian Paul
   *
   *
   * Marcus Geelnard:
   *   - Conversion to GLFW
   *   - Time based rendering (frame rate independent)
   *   - Slightly modified camera that should work better for stereo viewing
   *
   *
   * Camilla Löwy:
   *   - Removed FPS counter (this is not a benchmark)
   *   - Added a few comments
   *   - Enabled vsync
   */
  
  #if defined(_MSC_VER)
   // Make MS math.h define M_PI
   #define _USE_MATH_DEFINES
  #endif
  
  #include <math.h>
  #include <stdlib.h>
  #include <stdio.h>
  #include <string.h>
  
  #include <glad/glad.h>
  #define GLFW_INCLUDE_NONE
  #include <GLFW/glfw3.h>
  
  /**
  
    Draw a gear wheel.  You'll probably want to call this function when
    building a display list since we do a lot of trig here.
  
    Input:  inner_radius - radius of hole at center
            outer_radius - radius at center of teeth
            width - width of gear teeth - number of teeth
            tooth_depth - depth of tooth
  
   **/
  
  static void
  gear(GLfloat inner_radius, GLfloat outer_radius, GLfloat width,
    GLint teeth, GLfloat tooth_depth)
  {
    GLint i;
    GLfloat r0, r1, r2;
    GLfloat angle, da;
    GLfloat u, v, len;
  
    r0 = inner_radius;
    r1 = outer_radius - tooth_depth / 2.f;
    r2 = outer_radius + tooth_depth / 2.f;
  
    da = 2.f * (float) M_PI / teeth / 4.f;
  
    glShadeModel(GL_FLAT);
  
    glNormal3f(0.f, 0.f, 1.f);
  
    /* draw front face */
    glBegin(GL_QUAD_STRIP);
    for (i = 0; i <= teeth; i++) {
      angle = i * 2.f * (float) M_PI / teeth;
      glVertex3f(r0 * (float) cos(angle), r0 * (float) sin(angle), width * 0.5f);
      glVertex3f(r1 * (float) cos(angle), r1 * (float) sin(angle), width * 0.5f);
      if (i < teeth) {
        glVertex3f(r0 * (float) cos(angle), r0 * (float) sin(angle), width * 0.5f);
        glVertex3f(r1 * (float) cos(angle + 3 * da), r1 * (float) sin(angle + 3 * da), width * 0.5f);
      }
    }
    glEnd();
  
    /* draw front sides of teeth */
    glBegin(GL_QUADS);
    da = 2.f * (float) M_PI / teeth / 4.f;
    for (i = 0; i < teeth; i++) {
      angle = i * 2.f * (float) M_PI / teeth;
  
      glVertex3f(r1 * (float) cos(angle), r1 * (float) sin(angle), width * 0.5f);
      glVertex3f(r2 * (float) cos(angle + da), r2 * (float) sin(angle + da), width * 0.5f);
      glVertex3f(r2 * (float) cos(angle + 2 * da), r2 * (float) sin(angle + 2 * da), width * 0.5f);
      glVertex3f(r1 * (float) cos(angle + 3 * da), r1 * (float) sin(angle + 3 * da), width * 0.5f);
    }
    glEnd();
  
    glNormal3f(0.0, 0.0, -1.0);
  
    /* draw back face */
    glBegin(GL_QUAD_STRIP);
    for (i = 0; i <= teeth; i++) {
      angle = i * 2.f * (float) M_PI / teeth;
      glVertex3f(r1 * (float) cos(angle), r1 * (float) sin(angle), -width * 0.5f);
      glVertex3f(r0 * (float) cos(angle), r0 * (float) sin(angle), -width * 0.5f);
      if (i < teeth) {
        glVertex3f(r1 * (float) cos(angle + 3 * da), r1 * (float) sin(angle + 3 * da), -width * 0.5f);
        glVertex3f(r0 * (float) cos(angle), r0 * (float) sin(angle), -width * 0.5f);
      }
    }
    glEnd();
  
    /* draw back sides of teeth */
    glBegin(GL_QUADS);
    da = 2.f * (float) M_PI / teeth / 4.f;
    for (i = 0; i < teeth; i++) {
      angle = i * 2.f * (float) M_PI / teeth;
  
      glVertex3f(r1 * (float) cos(angle + 3 * da), r1 * (float) sin(angle + 3 * da), -width * 0.5f);
      glVertex3f(r2 * (float) cos(angle + 2 * da), r2 * (float) sin(angle + 2 * da), -width * 0.5f);
      glVertex3f(r2 * (float) cos(angle + da), r2 * (float) sin(angle + da), -width * 0.5f);
      glVertex3f(r1 * (float) cos(angle), r1 * (float) sin(angle), -width * 0.5f);
    }
    glEnd();
  
    /* draw outward faces of teeth */
    glBegin(GL_QUAD_STRIP);
    for (i = 0; i < teeth; i++) {
      angle = i * 2.f * (float) M_PI / teeth;
  
      glVertex3f(r1 * (float) cos(angle), r1 * (float) sin(angle), width * 0.5f);
      glVertex3f(r1 * (float) cos(angle), r1 * (float) sin(angle), -width * 0.5f);
      u = r2 * (float) cos(angle + da) - r1 * (float) cos(angle);
      v = r2 * (float) sin(angle + da) - r1 * (float) sin(angle);
      len = (float) sqrt(u * u + v * v);
      u /= len;
      v /= len;
      glNormal3f(v, -u, 0.0);
      glVertex3f(r2 * (float) cos(angle + da), r2 * (float) sin(angle + da), width * 0.5f);
      glVertex3f(r2 * (float) cos(angle + da), r2 * (float) sin(angle + da), -width * 0.5f);
      glNormal3f((float) cos(angle), (float) sin(angle), 0.f);
      glVertex3f(r2 * (float) cos(angle + 2 * da), r2 * (float) sin(angle + 2 * da), width * 0.5f);
      glVertex3f(r2 * (float) cos(angle + 2 * da), r2 * (float) sin(angle + 2 * da), -width * 0.5f);
      u = r1 * (float) cos(angle + 3 * da) - r2 * (float) cos(angle + 2 * da);
      v = r1 * (float) sin(angle + 3 * da) - r2 * (float) sin(angle + 2 * da);
      glNormal3f(v, -u, 0.f);
      glVertex3f(r1 * (float) cos(angle + 3 * da), r1 * (float) sin(angle + 3 * da), width * 0.5f);
      glVertex3f(r1 * (float) cos(angle + 3 * da), r1 * (float) sin(angle + 3 * da), -width * 0.5f);
      glNormal3f((float) cos(angle), (float) sin(angle), 0.f);
    }
  
    glVertex3f(r1 * (float) cos(0), r1 * (float) sin(0), width * 0.5f);
    glVertex3f(r1 * (float) cos(0), r1 * (float) sin(0), -width * 0.5f);
  
    glEnd();
  
    glShadeModel(GL_SMOOTH);
  
    /* draw inside radius cylinder */
    glBegin(GL_QUAD_STRIP);
    for (i = 0; i <= teeth; i++) {
      angle = i * 2.f * (float) M_PI / teeth;
      glNormal3f(-(float) cos(angle), -(float) sin(angle), 0.f);
      glVertex3f(r0 * (float) cos(angle), r0 * (float) sin(angle), -width * 0.5f);
      glVertex3f(r0 * (float) cos(angle), r0 * (float) sin(angle), width * 0.5f);
    }
    glEnd();
  
  }
  
  
  static GLfloat view_rotx = 20.f, view_roty = 30.f, view_rotz = 0.f;
  static GLint gear1, gear2, gear3;
  static GLfloat angle = 0.f;
  
  /* OpenGL draw function & timing */
  static void draw(void)
  {
    glClearColor(0.0, 0.0, 0.0, 0.0);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
  
    glPushMatrix();
      glRotatef(view_rotx, 1.0, 0.0, 0.0);
      glRotatef(view_roty, 0.0, 1.0, 0.0);
      glRotatef(view_rotz, 0.0, 0.0, 1.0);
  
      glPushMatrix();
        glTranslatef(-3.0, -2.0, 0.0);
        glRotatef(angle, 0.0, 0.0, 1.0);
        glCallList(gear1);
      glPopMatrix();
  
      glPushMatrix();
        glTranslatef(3.1f, -2.f, 0.f);
        glRotatef(-2.f * angle - 9.f, 0.f, 0.f, 1.f);
        glCallList(gear2);
      glPopMatrix();
  
      glPushMatrix();
        glTranslatef(-3.1f, 4.2f, 0.f);
        glRotatef(-2.f * angle - 25.f, 0.f, 0.f, 1.f);
        glCallList(gear3);
      glPopMatrix();
  
    glPopMatrix();
  }
  
  
  /* update animation parameters */
  static void animate(void)
  {
    angle = 100.f * (float) glfwGetTime();
  }
  
  
  /* change view angle, exit upon ESC */
  void key( GLFWwindow* window, int k, int s, int action, int mods )
  {
    if( action != GLFW_PRESS ) return;
  
    switch (k) {
    case GLFW_KEY_Z:
      if( mods & GLFW_MOD_SHIFT )
        view_rotz -= 5.0;
      else
        view_rotz += 5.0;
      break;
    case GLFW_KEY_ESCAPE:
      glfwSetWindowShouldClose(window, GLFW_TRUE);
      break;
    case GLFW_KEY_UP:
      view_rotx += 5.0;
      break;
    case GLFW_KEY_DOWN:
      view_rotx -= 5.0;
      break;
    case GLFW_KEY_LEFT:
      view_roty += 5.0;
      break;
    case GLFW_KEY_RIGHT:
      view_roty -= 5.0;
      break;
    default:
      return;
    }
  }
  
  
  /* new window size */
  void reshape( GLFWwindow* window, int width, int height )
  {
    GLfloat h = (GLfloat) height / (GLfloat) width;
    GLfloat xmax, znear, zfar;
  
    znear = 5.0f;
    zfar  = 30.0f;
    xmax  = znear * 0.5f;
  
    glViewport( 0, 0, (GLint) width, (GLint) height );
    glMatrixMode( GL_PROJECTION );
    glLoadIdentity();
    glFrustum( -xmax, xmax, -xmax*h, xmax*h, znear, zfar );
    glMatrixMode( GL_MODELVIEW );
    glLoadIdentity();
    glTranslatef( 0.0, 0.0, -20.0 );
  }
  
  
  /* program & OpenGL initialization */
  static void init(void)
  {
    static GLfloat pos[4] = {5.f, 5.f, 10.f, 0.f};
    static GLfloat red[4] = {0.8f, 0.1f, 0.f, 1.f};
    static GLfloat green[4] = {0.f, 0.8f, 0.2f, 1.f};
    static GLfloat blue[4] = {0.2f, 0.2f, 1.f, 1.f};
  
    glLightfv(GL_LIGHT0, GL_POSITION, pos);
    glEnable(GL_CULL_FACE);
    glEnable(GL_LIGHTING);
    glEnable(GL_LIGHT0);
    glEnable(GL_DEPTH_TEST);
  
    /* make the gears */
    gear1 = glGenLists(1);
    glNewList(gear1, GL_COMPILE);
    glMaterialfv(GL_FRONT, GL_AMBIENT_AND_DIFFUSE, red);
    gear(1.f, 4.f, 1.f, 20, 0.7f);
    glEndList();
  
    gear2 = glGenLists(1);
    glNewList(gear2, GL_COMPILE);
    glMaterialfv(GL_FRONT, GL_AMBIENT_AND_DIFFUSE, green);
    gear(0.5f, 2.f, 2.f, 10, 0.7f);
    glEndList();
  
    gear3 = glGenLists(1);
    glNewList(gear3, GL_COMPILE);
    glMaterialfv(GL_FRONT, GL_AMBIENT_AND_DIFFUSE, blue);
    gear(1.3f, 2.f, 0.5f, 10, 0.7f);
    glEndList();
  
    glEnable(GL_NORMALIZE);
  }
  
  
  /* program entry */
  int main(int argc, char *argv[])
  {
      GLFWwindow* window;
      int width, height;
  
      if( !glfwInit() )
      {
          fprintf( stderr, "Failed to initialize GLFW\n" );
          exit( EXIT_FAILURE );
      }
  
      glfwWindowHint(GLFW_DEPTH_BITS, 16);
      glfwWindowHint(GLFW_TRANSPARENT_FRAMEBUFFER, GLFW_TRUE);
  
      window = glfwCreateWindow( 300, 300, "Gears", NULL, NULL );
      if (!window)
      {
          fprintf( stderr, "Failed to open GLFW window\n" );
          glfwTerminate();
          exit( EXIT_FAILURE );
      }
  
      // Set callback functions
      glfwSetFramebufferSizeCallback(window, reshape);
      glfwSetKeyCallback(window, key);
  
      glfwMakeContextCurrent(window);
      gladLoadGLLoader((GLADloadproc)glfwGetProcAddress);
      glfwSwapInterval( 1 );
  
      glfwGetFramebufferSize(window, &width, &height);
      reshape(window, width, height);
  
      // Parse command-line options
      init();
  
      // Main loop
      while( !glfwWindowShouldClose(window) )
      {
          // Draw gears
          draw();
  
          // Update animation
          animate();
  
          // Swap buffers
          glfwSwapBuffers(window);
          glfwPollEvents();
      }
  
      // Terminate GLFW
      glfwTerminate();
  
      // Exit program
      exit( EXIT_SUCCESS );
  }
  
  