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

#define WINDSIZEX 100
#define WINDSIZEY 100


void
init (void)
{
  glClearColor (0.0, 0.0, 0.0, 1.0);
  glDisable (GL_DITHER);
  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();
  glOrtho(-4.0, 4.0, -4.0, 4.0, 0.0, 1.0);
  glMatrixMode(GL_MODELVIEW);
  glLoadIdentity();
  glDrawBuffer(GL_FRONT);
  glReadBuffer(GL_FRONT);

}


static void
test (void)
{
  const GLfloat VertColor[4] = { 0.25, 0.75, 0.5, 0.25 };
  const GLfloat Param0[4] = { 0.0, 0.0, 0.0, 0.0 };
  const GLfloat Param2[4] = { -1.0, 0.0, 0.25, -0.5 };
  GLuint progID;
  int i;
  char progString[] = "!!ARBvp1.0\n"
                "PARAM p0 = program.local[0]; \n"
                "PARAM p2 = program.local[2]; \n"
                "MOV result.position, vertex.position; \n"
                "SLT result.color, p2, p0; \n"
                "END \n";

  glGenProgramsARB(1, &progID);
  glBindProgramARB(GL_VERTEX_PROGRAM_ARB, progID);
  glEnable(GL_VERTEX_PROGRAM_ARB);

  glColor4fv(VertColor);
  glProgramLocalParameter4fvARB(GL_VERTEX_PROGRAM_ARB, 0, Param0);
  glProgramLocalParameter4fvARB(GL_VERTEX_PROGRAM_ARB, 2, Param2);

  glProgramStringARB(GL_VERTEX_PROGRAM_ARB,
                                GL_PROGRAM_FORMAT_ASCII_ARB,
                                strlen(progString),
                                (const GLubyte *) progString);
  GLfloat r = 0.25;
  glDisable(GL_DEPTH_TEST);
  glClear(GL_COLOR_BUFFER_BIT);

  glBegin(GL_POLYGON);
    glTexCoord2f(0, 0);  glVertex2f(-r, -r);
    glTexCoord2f(1, 0);  glVertex2f( r, -r);
    glTexCoord2f(1, 1);  glVertex2f( r,  r);
    glTexCoord2f(0, 1);  glVertex2f(-r,  r);
  glEnd();

  GLfloat pixel[4];
  GLfloat expect[4] = {1, 0, 0, 1};
  glReadPixels(WINDSIZEX / 2, WINDSIZEY / 2, 1, 1, GL_RGBA, GL_FLOAT, pixel);
  for (i=0; i<4; i++) {
     printf("pixel[%d] = %f, should be %f\n", i, pixel[i], expect[i]);
  }
}

void
display (void)
{
  glMatrixMode (GL_PROJECTION);
  glLoadIdentity ();
  gluOrtho2D (0, WINDSIZEX, 0, WINDSIZEX);
  test ();
}

int
main (int argc, char **argv)
{
  glutInit (&argc, argv);
  glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);
  glutInitWindowSize (WINDSIZEX, WINDSIZEY);
  glutInitWindowPosition (100, 100);
  glutCreateWindow (argv[0]);
  init ();
  glutDisplayFunc (display);
  glutMainLoop ();
  return 0;

}