#include <err.h>
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <unistd.h>
#include <X11/Xlib.h>
#include <X11/extensions/Xrender.h>

#define WINSIZ 500

/* X Stuff */
Display *dpy;
int screen;
int depth;
Window root;
Visual *visual;
XRenderPictFormat *fmt;

/* Window */
Window win;
Pixmap background;
Picture drawingarea;
Picture white_brush;

Picture
create_brush(int red, int green, int blue, int alpha)
{
	XRenderColor color={.red=red, .green=green, .blue=blue, .alpha=alpha};
	
	Pixmap pm=XCreatePixmap(dpy, win, 1, 1, depth);
	XRenderPictureAttributes pict_attr;
	pict_attr.repeat=1;
	Picture picture=XRenderCreatePicture(dpy, pm, fmt, CPRepeat, &pict_attr);
	XRenderFillRectangle(dpy, PictOpOver, picture, &color, 0, 0, 1, 1);
	XFreePixmap(dpy, pm);
	
	return picture;
}

Window
initwin(void)
{
	Window win;

	win = XCreateWindow(dpy, root, 0, 0, WINSIZ, WINSIZ, 0,
	                       depth, InputOutput, visual, 0, NULL);
	background = XCreatePixmap(dpy, win, WINSIZ, WINSIZ, depth);
	XSelectInput(dpy, win, StructureNotifyMask);
	XSetWindowBackgroundPixmap(dpy, win, background);
	XMapWindow(dpy, win);
	return win;
}

Picture
initdrawingarea(void)
{
	XRenderPictureAttributes pict_attr;
	Picture drawingarea;

	pict_attr.poly_edge = PolyEdgeSmooth;
	pict_attr.poly_mode = PolyModeImprecise;
	drawingarea = XRenderCreatePicture(dpy, background, fmt, CPPolyEdge|CPPolyMode,
		&pict_attr);

	return drawingarea;
}

void
drawarc(Picture src, Picture dst, int cx, int cy, int radius, int angle1, int angle2)
{
	XTriangle *tri;
	int angle = angle2 - angle1;
	int a;
	int i;

	if (angle < 1 || angle > 360 * 64)
		errx(1, "could not draw arc");
	if ((tri = calloc(angle, sizeof *tri)) == NULL)
		err(1, "calloc");
	a = angle1;
	for (i = 0; i < angle; i++) {
		tri[i].p1.x = cx << 16;
		tri[i].p1.y = cy << 16;
		tri[i].p2.x = (cx << 16) + (radius << 16) * cos((a * M_PI) / (180 * 64));
		tri[i].p2.y = (cy << 16) - (radius << 16) * sin((a * M_PI) / (180 * 64));
		a++;
		tri[i].p3.x = (cx << 16) + (radius << 16) * cos((a * M_PI) / (180 * 64));
		tri[i].p3.y = (cy << 16) - (radius << 16) * sin((a * M_PI) / (180 * 64));
	}
	XRenderCompositeTriangles (dpy, PictOpOver, src, dst, 0, 0, 0, tri, angle);

	free(tri);
}

int
main()
{
	int da, db;     /* dummy variables */
	XRenderColor black = {0,0,0,0xffff};

	if ((dpy = XOpenDisplay(NULL)) == NULL)
		errx(1, "could not open display");
	if (!XRenderQueryExtension(dpy, &da, &db))
		errx(1, "RENDER extension missing");
	screen = DefaultScreen(dpy);
	root = DefaultRootWindow(dpy);
	visual = DefaultVisual(dpy, screen);
	depth = DefaultDepth(dpy, screen);
	fmt = XRenderFindVisualFormat(dpy, visual);

	win = initwin();
	drawingarea = initdrawingarea();
	white_brush = create_brush(0xffff, 0xffff, 0xffff, 0xffff);
	
	while(1) {
		XFlush(dpy);
		
		XRenderFillRectangle(dpy, PictOpOver, drawingarea, &black,
			0, 0, 640, 480);

		drawarc(white_brush, drawingarea, WINSIZ/2, WINSIZ/2, WINSIZ/2, 0, 90 * 64);

		XClearArea(dpy, win, 0, 0, 640, 480, 0);
		usleep(20*1000);
	}
	
	return 0;
}