/* pick.c                                   */
/* demonstrates picking used selection mode */
/* E. Angel, Interactive Computer Graphics  */

#include <stdlib.h>
#include <stdio.h>
#include <GL/glut.h>

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

void drawObjects(GLenum mode)
{
  if(mode == GL_SELECT) glLoadName(1);
  glColor3f(1.0, 0.0, 0.0);
  glRectf(-0.5, -0.5, 1.0, 1.0);
  if(mode == GL_SELECT) glLoadName(2);
  glColor3f(0.0, 0.0, 1.0);
  glRectf(-1.0, -1.0, 0.5, 0.5);
}

void display(void)
{
  glClear(GL_COLOR_BUFFER_BIT);
  drawObjects(GL_RENDER);
  glFlush();
}

/*  processHits prints out the contents of the 
    selection array. */
void processHits (GLint hits, GLuint buffer[])
{
  unsigned int i, j;
  GLuint ii, jj, names, *ptr;

  printf ("hits = %d\n", hits);
  ptr = (GLuint *) buffer; 
  for (i = 0; i < hits; i++) /*  for each hit  */
  {
    names = *ptr;
    ptr+=3;
    for (j = 0; j < names; j++) /*  for each name */
    {
       if(*ptr==1) printf ("red rectangle\n");
       else printf ("blue rectangle\n");
       ptr++;
    }
    /* printf ("\n"); */
  }
}

#define SIZE 512
void mouse(int button, int state, int x, int y)
{
  GLuint selectBuf[SIZE];
  GLint hits;
  GLint viewport[4];

  if (button == GLUT_LEFT_BUTTON && state == GLUT_DOWN) 
  {
    glGetIntegerv (GL_VIEWPORT, viewport);
    glSelectBuffer (SIZE, selectBuf);
    glRenderMode(GL_SELECT);

    glInitNames();
    glPushName(0);

    glMatrixMode (GL_PROJECTION);
    glPushMatrix ();
    glLoadIdentity ();
    /*  create 5x5 pixel picking region near cursor location */
    gluPickMatrix ((GLdouble) x, (GLdouble) (viewport[3] - y), 
                  5.0, 5.0, viewport);
    gluOrtho2D (-2.0, 2.0, -2.0, 2.0);
    drawObjects(GL_SELECT);
    glMatrixMode (GL_PROJECTION);
    glPopMatrix ();
    glFlush ();
    hits = glRenderMode (GL_RENDER);
    processHits (hits, selectBuf);
    glutPostRedisplay();
  }
} 

void reshape(int w, int h)
{
  glViewport(0, 0, w, h);
  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();
  gluOrtho2D (-2.0, 2.0, -2.0, 2.0);
  glMatrixMode(GL_MODELVIEW);
  glLoadIdentity();
}

void keyboard(unsigned char key, int x, int y)
{
  switch (key)
  {
    case 'q':
      exit(0);
      break;
  }
}

int main(int argc, char* argv[])
{
   glutInit(&argc, argv);
   glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);
   glutInitWindowSize (500, 500);
   glutInitWindowPosition (100, 100);
   glutCreateWindow (argv[0]);
   init();
   glutReshapeFunc(reshape);
   glutDisplayFunc(display); 
   glutMouseFunc(mouse);
   glutKeyboardFunc(keyboard);
   glutMainLoop();
   return 0; 
}