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

static const char *vs = 
"attribute vec4 vPosition;\n"
"uniform float uPointSize;\n"
"void main()\n"
"{\n"
"	gl_Position = vec4(0.0, 0.0, 0.0, 1.0);\n"
"}\n";

static const char *ps =
"#version 120\n"
"void main()\n"
"{\n"
"	gl_FragColor = vec4(gl_PointCoord.x, gl_PointCoord.y, 0, 1);\n"
"}\n";

static GLuint shader_stuff()
{
	GLuint shaderProgram;
	GLuint vertexShader, fragmentShader;

	char buf[4096];
	int len;
	GLuint link_status;

	vertexShader = glCreateShader(GL_VERTEX_SHADER);
	fragmentShader = glCreateShader(GL_FRAGMENT_SHADER);

	glShaderSource(vertexShader, 1, &vs, NULL);
	glShaderSource(fragmentShader, 1, &ps, NULL);

	glCompileShader(vertexShader);
	glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &link_status);
	if (link_status == 0) {
		printf("compile vertex shader failed!\n");

		glGetShaderInfoLog(vertexShader, sizeof(buf), &len, buf);
		printf("%s\n", buf);
	}


	glCompileShader(fragmentShader);
	glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &link_status);
	if (link_status == 0) {
		printf("compile fragment shader failed!\n");

		glGetShaderInfoLog(fragmentShader, sizeof(buf), &len, buf);
		printf("%s\n", buf);
	}

	shaderProgram = glCreateProgram();

	glAttachShader(shaderProgram, vertexShader);
	glAttachShader(shaderProgram, fragmentShader);


	/*
	 * here bind  vPosition
	 */
	glBindAttribLocation(shaderProgram, 0, "vPosition");

	glLinkProgram(shaderProgram);

	glGetProgramiv(shaderProgram, GL_LINK_STATUS, &link_status);
	if (link_status == 0) {
		printf("Link failed!\n");

		glGetProgramInfoLog(shaderProgram, sizeof(buf), &len, buf);
		printf("%s\n", buf);

		exit(1);
	}


	return shaderProgram;
}

int use_fbo =  0;

void myDisplay(void)
{							
	GLuint point_size_loc;
	GLuint program;
	GLubyte pixels[100 * 100 * 4];

	static int called = 0;
	if (called)
		return;
	called = 1;


	if (1) {
		GLuint vbo;
		GLuint fbo;
		GLfloat vertices[] = {
			0, 0,
		};

		if (use_fbo) {
			GLuint color_buffer;
			GLuint depth_buffer;

			glGenRenderbuffers(1, &color_buffer);
			glGenRenderbuffers(1, &depth_buffer);
			glBindRenderbuffer(GL_RENDERBUFFER, color_buffer);
			glRenderbufferStorage(GL_RENDERBUFFER, GL_RGBA, 100, 100);

			glBindRenderbuffer(GL_RENDERBUFFER, depth_buffer);
			glRenderbufferStorage(GL_RENDERBUFFER, GL_DEPTH_COMPONENT24, 100, 100);

			glGenFramebuffers(1, &fbo);
			glBindFramebuffer(GL_FRAMEBUFFER, fbo);
			glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, color_buffer);
			glFramebufferRenderbuffer(GL_DRAW_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_RENDERBUFFER, depth_buffer);
		}

		glClearColor(0, 0, 0, 1);
		glClear(GL_COLOR_BUFFER_BIT);

		program = shader_stuff();
		glUseProgram(program);


		glEnable(GL_POINT_SPRITE_ARB);
		glPointSize(50);
		glBegin(GL_POINTS);
			glVertex2f(0.0, 0.0);
		glEnd();

		if (use_fbo) {
			glBindFramebuffer(GL_READ_FRAMEBUFFER, fbo);
			glReadPixels(0, 0, 100, 100, GL_RGBA, GL_UNSIGNED_BYTE, pixels);
		}
	}

	if (use_fbo) {
		glBindFramebuffer(GL_DRAW_FRAMEBUFFER, 0);
		
		glDrawPixels(100, 100, GL_RGBA, GL_UNSIGNED_BYTE, pixels);
		//glBlitFramebuffer(0,0,100,100,0,0,100,100,GL_COLOR_BUFFER_BIT,GL_NEAREST); 
	}

	glFlush();
}

int main(int argc,char** argv)
{
	glutInit(&argc,argv);
	glutInitDisplayMode(GLUT_SINGLE|GLUT_RGB);
	glutInitWindowSize(100, 100);
	glutInitWindowPosition(100,100);
	glutCreateWindow("point-coord");
	glutDisplayFunc(myDisplay);

	if (argv[1] && strcmp(argv[1], "--use-fbo") == 0)
		use_fbo = 1;
	glutMainLoop();
	return 0;
}