examples/gears.c

/*
 * 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>

#define GLAD_GL_IMPLEMENTATION
#include <glad/gl.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);
    gladLoadGL(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 );
}