/*
 * Copyright (C) 2010 Nick Bowler
 *
 * License WTFPL2: Do What The Fuck You Want To Public License, version 2.
 * This is free software: you are free to do what the fuck you want to.
 * There is NO WARRANTY, to the extent permitted by law.
 *
 * In case the above is not acceptable, you may alternately choose the terms
 * of the MIT license: http://opensource.org/licenses/mit-license.php.
 */
#include <stdio.h>
#include <stdlib.h>
#include <math.h>

#include <GL/glew.h>
#include <GL/glut.h>

#ifndef XRES
#	define XRES 32
#endif
#ifndef YRES
#	define YRES 32
#endif

static float pixbuf[YRES][XRES];

void display(void)
{
	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

	for (unsigned i = 0; i < YRES; i++) {
		for (unsigned j = 0; j < XRES; j++) {
			if (isfinite(pixbuf[i][j])) {
				glPointSize(pixbuf[i][j]);
				glBegin(GL_POINTS);
				glVertex2d(j, i);
				glEnd();
			}
		}
	}

	glutSwapBuffers();
}

void reshape(int width, int height)
{
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	glViewport(0, 0, width, height);
	glOrtho(0, XRES, 0, YRES, -1, 1);
	glMatrixMode(GL_MODELVIEW);
}

void drawTeapot(size_t w, size_t h)
{
	glPushAttrib(GL_VIEWPORT_BIT | GL_COLOR_BUFFER_BIT | GL_TRANSFORM_BIT);
	glViewport(0, 0, w, h);

	glClearColor(0, 0, 0, 0);

	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

	glMatrixMode(GL_PROJECTION);
	glPushMatrix();
	glLoadIdentity();
	gluPerspective(40.0, 1, 0.1, 10.0);

	glMatrixMode(GL_MODELVIEW);
	glPushMatrix();
	glLoadIdentity();
	glTranslated(0, 0, -5);

	glColor3d(1, 1, 1);
	glutSolidTeapot(1);

	glPopMatrix();
	glMatrixMode(GL_PROJECTION);
	glPopMatrix();

	glPopAttrib();
}

void rasterTeapot(float *pixels, size_t w, size_t h)
{
	GLuint fbo, buffers[2];

	glGenFramebuffersEXT(1, &fbo);
	glGenRenderbuffersEXT(2, buffers);

	glBindRenderbufferEXT(GL_RENDERBUFFER_EXT, buffers[0]);
	glRenderbufferStorageEXT(GL_RENDERBUFFER_EXT, GL_RGB8, w, h);

	glBindRenderbufferEXT(GL_RENDERBUFFER_EXT, buffers[1]);
	glRenderbufferStorageEXT(GL_RENDERBUFFER_EXT, GL_DEPTH_COMPONENT, w, h);

	glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, fbo);
	glFramebufferRenderbufferEXT(GL_FRAMEBUFFER_EXT,
		GL_COLOR_ATTACHMENT0_EXT, GL_RENDERBUFFER_EXT, buffers[0]);
	glFramebufferRenderbufferEXT(GL_FRAMEBUFFER_EXT,
		GL_DEPTH_ATTACHMENT_EXT, GL_RENDERBUFFER_EXT, buffers[1]);

	drawTeapot(w, h);

	glPixelTransferf(GL_DEPTH_SCALE, -1);
	glPixelTransferf(GL_DEPTH_BIAS,   1);

	glReadPixels(0, 0, w, h, GL_DEPTH_COMPONENT, GL_FLOAT, pixels);
	for (unsigned i = 0; i < w*h; i++) {
		if (pixels[i] == 0)
			pixels[i] = -INFINITY;
		pixels[i] *= 1200;
		pixels[i] -= 11;
	}

	glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0);
	glDeleteFramebuffersEXT(1, &fbo);
	glDeleteRenderbuffersEXT(2, buffers);
}

int main(int argc, char **argv)
{
	GLenum err;
	int window;

	glutInit(&argc, argv);
	glutInitDisplayMode(GLUT_RGB | GLUT_DEPTH | GLUT_DOUBLE);

	window = glutCreateWindow("GLTest");
	if (window == 0)
		return EXIT_FAILURE;
	glutSetWindow(window);

	err = glewInit();
	if (err != GLEW_OK) {
		fprintf(stderr, "glewInit: %s\n", glewGetErrorString(err));
		return EXIT_FAILURE;
	}

	glEnable(GL_DEPTH_TEST);
	glEnable(GL_POINT_SMOOTH);
	rasterTeapot(pixbuf[0], XRES, YRES);

	glutDisplayFunc(display);
	glutReshapeFunc(reshape);
	glutMainLoop();
	return 0;
}