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


#define WIN_WIDTH 100
#define WIN_HEIGHT 100
#define TEX_WIDTH 8
#define TEX_HEIGHT 4

#define EPSILON_R 0.4
#define EPSILON_G 0.4
#define EPSILON_B 0.4
#define EPSILON_A 0.4

GLfloat read_buf[4 * TEX_WIDTH * TEX_HEIGHT];
GLfloat tex_image2d[TEX_WIDTH][TEX_HEIGHT][3];
GLint tex_name = 1;


void init()
{
	glMatrixMode(GL_MODELVIEW);
	glLoadIdentity();
	glTranslatef(-1.0, -1.0, 0.0);
	glScalef(2.0/WIN_WIDTH, 2.0/WIN_HEIGHT, 1.0);

	glClearColor(0.0, 0.0, 0.0, 0.3);
	glClear(GL_COLOR_BUFFER_BIT);

	glDisable (GL_DITHER);
}


int check_pixels(GLint llx, GLint lly, GLint w, GLint h, 
			GLfloat exp_r, GLfloat exp_g,
			GLfloat exp_b, GLfloat exp_a)
{
	GLfloat *buf = NULL, color_r, color_g, color_b, color_a;
	int x, y, pixel;

	buf = (GLfloat *)malloc(w * h * sizeof(GLfloat) * 4);
	if (buf == NULL)
		return -2;
	
	glReadPixels(llx, lly, w, h, GL_RGBA, GL_FLOAT, buf);
	
        for (y = 0; y < h; y ++) {
        for (x = 0; x < w; x ++) {
                pixel = x + y * w;
		color_r = buf[pixel*4];
		color_g =  buf[pixel*4+1];
		color_b =  buf[pixel*4+2];
		color_a =  buf[pixel*4+3];

		if (fabsf(color_r - exp_r) > EPSILON_R ||
		    fabsf(color_g - exp_g) > EPSILON_G ||
		    fabsf(color_b - exp_b) > EPSILON_B ||
		    fabsf(color_a - exp_a) > EPSILON_A)  {

                	printf("pixel[%d, %d]: %f %f %f %f\n", x, y,
                        	buf[pixel*4], buf[pixel*4+1],
	                        buf[pixel*4+2], buf[pixel*4+3]);
		}
        }
        }

	printf("\ncheck pixels done.\n");
	if (buf)
		free(buf);

	return 0;
}



void display()
{
	GLint i, read_w = 0, read_h = 0, x = 0, y = 0, pixel;
	
	glClear(GL_COLOR_BUFFER_BIT);
	if (glIsEnabled(GL_ALPHA_TEST) == GL_FALSE)
		printf("Alpha test is disabled \n");

	glColor4f(0.0, 0.1, 1.0, 0.8);
	glBegin(GL_QUAD_STRIP);
		glVertex2i(10, 10);
		glVertex2i(10, 60);
		glVertex2i(60, 10);
		glVertex2i(60, 60);
	glEnd();

	check_pixels(10, 10, 50, 50, 0.0, 0.1, 1.0, 0.8);

	glutSwapBuffers();

}


int main(int argc, char** argv)
{
	glutInit(&argc, argv);
	glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGBA);
	glutInitWindowSize (WIN_WIDTH, WIN_HEIGHT);
	glutInitWindowPosition (100, 100);
	glutCreateWindow ("hello");
	init();
	glutDisplayFunc(display);
	glutMainLoop();
}