double.c

// from the OpenGL Redbook
// simple square with mouse interactions

#include <GL/glut.h>

static GLfloat spin = 0.0;

void init(void){
  glClearColor(0.0, 0.0, 0.0, 0.0);
  glShadeModel(GL_FLAT);
}

void display(void){
  glClear(GL_COLOR_BUFFER_BIT);
  glPushMatrix();
  glRotatef(spin, 0.0, 0.0, 1.0);
  glColor3f(1.0, 1.0, 1.0);
  glRectf(-25.0, -25.0, 25.0, 25.0);
  glPopMatrix();
  glutSwapBuffers();
}

void spinDisplay(void){
  spin = spin + 2.0;
  if(spin > 360.0)
    spin = spin - 360.0;
  glutPostRedisplay();
}

// define coordinate grid (2D for now)
// handles recreating/drawing the window when moving/resizing
void reshape(int w, int h){
  glViewport(0, 0, (GLsizei) w, (GLsizei) h);
  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();
  glOrtho(-50.0, 50.0, -50.0, 50.0, -1.0, 1.0);
  glMatrixMode(GL_MODELVIEW);
  glLoadIdentity();
}

void mouse(int button, int state, int x, int y){
  switch(button){
    case GLUT_LEFT_BUTTON:
      if(state == GLUT_DOWN)
        glutIdleFunc(spinDisplay);
      break;
      
    case GLUT_MIDDLE_BUTTON:
      if(state == GLUT_DOWN)
        glutIdleFunc(NULL);
      break;

    default:
      break;
  }
}

// request double buffer display mode
// register mouse input callback functions
int main(int argc, char** argv){
  glutInit(&argc, argv);
  glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);
  glutInitWindowSize(250, 250);
  glutInitWindowPosition(100, 100);
  glutCreateWindow(argv[0]);
  init();
  glutDisplayFunc(display);
  glutReshapeFunc(reshape);
  glutMouseFunc(mouse);
  glutMainLoop();
  return 0;
}