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

#define WINDSIZEX 100
#define WINDSIZEY 100

GLfloat t[] = {
        0.0, 1.0, 0.0, 0.0, 1.0, 0.0,   0.0, 1.0, 0.0, 0.0, 1.0, 0.0,
        0.0, 1.0, 0.0, 0.0, 1.0, 0.0,   0.0, 1.0, 0.0, 0.0, 1.0, 0.0,
        0.0, 1.0, 0.0, 0.0, 1.0, 0.0,   0.0, 1.0, 0.0, 0.0, 1.0, 0.0,
        0.0, 1.0, 0.0, 0.0, 1.0, 0.0,   0.0, 1.0, 0.0, 0.0, 1.0, 0.0,
        0.0, 1.0, 0.0, 0.0, 1.0, 0.0,   0.0, 1.0, 0.0, 0.0, 1.0, 0.0,
        0.0, 1.0, 0.0, 0.0, 1.0, 0.0,   0.0, 1.0, 0.0, 0.0, 1.0, 0.0,
        0.0, 1.0, 0.0, 0.0, 1.0, 0.0,   0.0, 1.0, 0.0, 0.0, 1.0, 0.0,
        0.0, 1.0, 0.0, 0.0, 1.0, 0.0,   0.0, 1.0, 0.0, 0.0, 1.0, 0.0,
        0.0, 1.0, 0.0, 0.0, 1.0, 0.0,   0.0, 1.0, 0.0, 0.0, 1.0, 0.0,
        0.0, 1.0, 0.0, 0.0, 1.0, 0.0,   0.0, 1.0, 0.0, 0.0, 1.0, 0.0,
        0.0, 1.0, 0.0, 0.0, 1.0, 0.0,   0.0, 1.0, 0.0, 0.0, 1.0, 0.0,
        0.0, 1.0, 0.0, 0.0, 1.0, 0.0,   0.0, 1.0, 0.0, 0.0, 1.0, 0.0,
        0.0, 1.0, 0.0, 0.0, 1.0, 0.0,   0.0, 1.0, 0.0, 0.0, 1.0, 0.0,
        0.0, 1.0, 0.0, 0.0, 1.0, 0.0,   0.0, 1.0, 0.0, 0.0, 1.0, 0.0,
        0.0, 1.0, 0.0, 0.0, 1.0, 0.0,   0.0, 1.0, 0.0, 0.0, 1.0, 0.0,
        0.0, 1.0, 0.0, 0.0, 1.0, 0.0,   0.0, 1.0, 0.0, 0.0, 1.0, 0.0,
    };

void draw_first(void)
{
    glClear(GL_COLOR_BUFFER_BIT);

    glTexImage2D(GL_TEXTURE_2D, 0, 3, 8, 8, 0, GL_RGB, GL_FLOAT,
                 (unsigned char *)t);
    glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);

    glEnable(GL_TEXTURE_2D);
    glBegin(GL_QUAD_STRIP);
        glTexCoord2f(0.25, 0.25);
        glVertex2i(25, 25);
        glTexCoord2f(0.25, 0.75);
        glVertex2i(25, 75);
        glTexCoord2f(0.75, 0.25);
        glVertex2i(75, 25);
        glTexCoord2f(0.75, 0.75);
        glVertex2i(75, 75);
    glEnd();

    glDisable(GL_TEXTURE_2D);
}

void test()
{
    GLfloat buf[3];

    glTexImage2D(GL_TEXTURE_2D, 0, 3, 8, 8, 0, GL_RGB, GL_FLOAT,
                 (unsigned char *)t);
    glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);

    glClear(GL_COLOR_BUFFER_BIT);

    glColor3f(1.0, 1.0, 1.0);
    glBegin(GL_QUAD_STRIP);
        glTexCoord2f(0.25, 0.25);
        glVertex2i(25, 25);
        glTexCoord2f(0.25, 0.75);
        glVertex2i(25, 75);
        glTexCoord2f(0.75, 0.25);
        glVertex2i(75, 25);
        glTexCoord2f(0.75, 0.75);
        glVertex2i(75, 75);
    glEnd();
    glFlush();

    glEnable(GL_TEXTURE_2D);
    glBegin(GL_QUAD_STRIP);
        glTexCoord2f(0.25, 0.25);
        glVertex2i(25, 25);
        glTexCoord2f(0.25, 0.75);
        glVertex2i(25, 75);
        glTexCoord2f(0.75, 0.25);
        glVertex2i(75, 25);
        glTexCoord2f(0.75, 0.75);
        glVertex2i(75, 75);
    glEnd();


    glReadPixels(35, 50, 1, 1, GL_RGB, GL_FLOAT, buf);

    printf("get color: %f %f %f\n", buf[0], buf[1], buf[2]);
    if (fabs(buf[0] - 0.0) > 0.49 ||
        fabs(buf[1] - 1.0) > 0.49 ||
        fabs(buf[2] - 0.0) > 0.49) {
        printf("expect color: 0 1 0 \n");
    //    exit(-1);
    }else
        printf("success\n");
}

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

void display(void)
{
    glViewport(0, 0, WINDSIZEX, WINDSIZEY);
        glMatrixMode(GL_PROJECTION);
        glLoadIdentity();
    gluOrtho2D(0, WINDSIZEX, 0, WINDSIZEY);
        glMatrixMode(GL_MODELVIEW);
        glLoadIdentity();

    draw_first();
    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; 
}