/*
 * Compile with:
 *
 * gcc -g -Wall -o gl-texture gl-texture.c `pkg-config --cflags --libs gl glu` -lglut
 *
 * Based on:
 * Simple GLUT program to measure triangle strip rendering speed.
 * Brian Paul  February 15, 1997  This file is in the public domain.
 */

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


#define SIZE 64

static void Display( void )
{
   glClearColor( 1.0, 1.0, 1.0, 1.0 );
   glClear( GL_COLOR_BUFFER_BIT );

   glBegin(GL_QUADS);
   glTexCoord2f(0, 0);
   glVertex2f(0, 0);
   glTexCoord2f(SIZE, 0);
   glVertex2f(SIZE, 0);
   glTexCoord2f(SIZE, SIZE);
   glVertex2f(SIZE, SIZE);
   glTexCoord2f(0, SIZE);
   glVertex2f(0, SIZE);
   glEnd();
   glFinish();

   glutSwapBuffers();
}


static void Reshape( int width, int height )
{
   glViewport( 0, 0, width, height );
   glMatrixMode( GL_PROJECTION );
   glLoadIdentity();
   glOrtho(0.0, width, 0.0, height, -1.0, 1.0);
   glMatrixMode( GL_MODELVIEW );
   glLoadIdentity();
}


static void Key( unsigned char key, int x, int y )
{
   (void) x;
   (void) y;
   switch (key) {
      case 27:
         exit(0);
         break;
   }
   glutPostRedisplay();
}


static void LoadTex()
{
   GLubyte *pixels;
   int x, y;
   pixels = (GLubyte *) malloc(3*SIZE*SIZE);
   for (y = 0; y < SIZE; ++y)
      for (x = 0; x < SIZE; ++x) {
	  if ((x / 4 + y / 4) % 2 == 0) {
	      pixels[(y*SIZE+x)*3+0] = 0;
	      pixels[(y*SIZE+x)*3+1] = 0;
	      pixels[(y*SIZE+x)*3+2] = 0;
	  } else {
	      pixels[(y*SIZE+x)*3+0] = 255;
	      pixels[(y*SIZE+x)*3+1] = 255;
	      pixels[(y*SIZE+x)*3+2] = 255;
	  }
      }
   glEnable(GL_TEXTURE_RECTANGLE_ARB);
   glTexImage2D(GL_TEXTURE_RECTANGLE_ARB, 0, GL_RGB8, SIZE, SIZE, 0, GL_RGB, GL_UNSIGNED_BYTE, pixels);
   glTexParameteri(GL_TEXTURE_RECTANGLE_ARB, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
   glTexParameteri(GL_TEXTURE_RECTANGLE_ARB, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
}


static void Init( int argc, char *argv[] )
{
   LoadTex();

   glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_COMBINE);
   glTexEnvi(GL_TEXTURE_ENV, GL_COMBINE_RGB, GL_REPLACE);
   glTexEnvi(GL_TEXTURE_ENV, GL_COMBINE_ALPHA, GL_REPLACE);
   glEnable(GL_BLEND);
   glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);
}


int main( int argc, char *argv[] )
{
   glutInit( &argc, argv );
   glutInitWindowSize( (int) SIZE, (int) SIZE );
   glutInitWindowPosition( 0, 0 );

   glutInitDisplayMode( GLUT_RGB | GLUT_DOUBLE );

   glutCreateWindow( argv[0] );

   Init( argc, argv );
   Reshape( SIZE, SIZE );

   glutKeyboardFunc( Key );
   glutDisplayFunc( Display );

   glutMainLoop();
   return 0;

}