#include <assert.h>
#include <GL/glut.h>
#include <GL/glext.h>

static void
reshape(int width, int height)
{
  glViewport(0, 0, width, height);
 
  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();
  glOrtho(0, width, 0, height, -1.0, 100.0);

  assert(glGetError() == GL_NO_ERROR);
}

static void
display(void)
{
  glClearColor(0.3f, 0.3f, 0.3f, 1.0f);
  glClear(GL_COLOR_BUFFER_BIT);

  glMatrixMode(GL_MODELVIEW);
  glLoadIdentity();

  glPushMatrix();
  glTranslated(20.0, 20.0, 0.0);
  glBegin(GL_TRIANGLES);
    glColor3d(100.0, 0.0, 0.0);
    glVertex3d(0.0, 0.0, 0.0);
    glColor3d(0.0, 100.0, 0.0);
    glVertex3d(100.0, 0.0, 0.0);
    glColor3d(0.0, 0.0, 100.0);
    glVertex3d(100.0, 100.0, 0.0);
  glEnd();
  glPopMatrix();

  glutSwapBuffers();
}

int
main(int argc, char **argv)
{
  glutInit(&argc, argv);
  glutCreateWindow("Immediate mode triangle");
  glutReshapeFunc(reshape);
  glutDisplayFunc(display);
  glutIdleFunc(glutPostRedisplay);

  glutMainLoop();
  return 0;
}