/*
 * 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 <math.h>

#include <X11/Xlib.h>
#include <GL/gl.h>
#include <GL/glx.h>

#ifndef M_PI
#	define M_PI 3.14159265358979323844
#endif

static void resize(int w, int h)
{
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	glViewport(0, 0, w, h);
	glOrtho(-1.2, 1.2, -1.2, 1.2, -1, 1);
	glMatrixMode(GL_MODELVIEW);
}

static void render(double theta)
{
	glClear(GL_COLOR_BUFFER_BIT);

	glBegin(GL_LINE_LOOP);
	glVertex2d(0, 0);
	glVertex2d(cos(theta-0.1), sin(theta-0.1));
	glVertex2d(cos(theta+0.1), sin(theta+0.1));
	glEnd();

	glFinish();
}

int main(int argc, char **argv)
{
	int rgb_attribs[] = {
		GLX_RGBA,
		GLX_RED_SIZE, 1,
		GLX_GREEN_SIZE, 1,
		GLX_BLUE_SIZE, 1,
		GLX_DOUBLEBUFFER,
		None
	};
	Display *dpy;
	XVisualInfo *vi;
	GLXContext ctx1, ctx2;
	Window win, win1, win2;
	XSetWindowAttributes attr;
	double theta = 0;

	dpy = XOpenDisplay(NULL);
	vi = glXChooseVisual(dpy, DefaultScreen(dpy), rgb_attribs);

	attr.colormap = XCreateColormap(dpy, RootWindow (dpy, vi->screen),
	                                vi->visual, AllocNone);
	win = XCreateWindow(dpy, DefaultRootWindow(dpy),
			     0, 0, 600, 300, 0,
			     vi->depth, InputOutput, vi->visual,
			     CWColormap, &attr);
	XMapWindow(dpy, win);

	win1 = XCreateWindow(dpy, win, 0, 0, 300, 300, 0, 
	                     vi->depth, InputOutput, vi->visual,
	                     CWColormap, &attr);
	XSelectInput(dpy, win1, ExposureMask);
	XMapWindow(dpy, win1);

	win2 = XCreateWindow(dpy, win, 300, 0, 300, 300, 0, 
	                     vi->depth, InputOutput, vi->visual,
	                     CWColormap, &attr);
	XSelectInput(dpy, win2, ExposureMask);
	XMapWindow(dpy, win2);

	ctx1 = glXCreateContext(dpy, vi, NULL, True);
	ctx2 = glXCreateContext(dpy, vi, NULL, True);

	while (1) {
		/* discard pending events. */
		XSync(dpy, True);

		glXMakeCurrent(dpy, win1, ctx1);
		resize(300, 300);
		render(theta);
		glXSwapBuffers(dpy, win1);

		/* recreate context to try and trigger lockup */
		glXDestroyContext(dpy, ctx2);
		ctx2 = glXCreateContext(dpy, vi, NULL, True);

		glXMakeCurrent(dpy, win2, ctx2);
		resize(300, 300);
		render(-(theta+M_PI));
		glXSwapBuffers(dpy, win2);

		theta = remainder(theta + M_PI/180, 2*M_PI);
	}

	return 0;
}