#include <stdio.h>
#include <X11/Xlib.h>
#include <X11/Xutil.h>
#include <X11/extensions/Xrender.h>

int main(int argc, char **argv)
{
    Display *display;
    int event_base, error_base;
    Screen *screen;
    Window root, window1, window2;
    unsigned long black;
    XRenderPictFormat *format;
    struct c
    {
	XRectangle rect;
	Picture pict;
	XRenderColor color;
	struct c *c;
    } c1, c2;
    XContext context;

    display = XOpenDisplay(NULL);
    if (display == NULL)
    {
	return 1;
    }

    if (!XRenderQueryExtension(display, &event_base, &error_base))
    {
	XCloseDisplay(display);
	return 1;
    }

    screen = DefaultScreenOfDisplay(display);
    root = RootWindowOfScreen(screen);
    black = BlackPixelOfScreen(screen);
    window1 = XCreateSimpleWindow(display, root, 0, 0, 400, 300, 1, black, black);
    window2 = XCreateSimpleWindow(display, root, 0, 0, 300, 400, 1, black, black);
    XSelectInput(display, window1, KeyPressMask | ButtonPressMask | ExposureMask | StructureNotifyMask);
    XSelectInput(display, window2, KeyPressMask | ButtonPressMask | ExposureMask | StructureNotifyMask);
    XMapWindow(display, window1);
    XMapWindow(display, window2);

    format = XRenderFindVisualFormat(display, DefaultVisualOfScreen(screen));
    c1.pict = XRenderCreatePicture(display, window1, format, 0, NULL);
    c2.pict = XRenderCreatePicture(display, window2, format, 0, NULL);

    context = XUniqueContext();
    XSaveContext(display, window1, context, (XPointer)&c1);
    XSaveContext(display, window2, context, (XPointer)&c2);

    c1.color.red = 0;
    c1.color.green = 0xffff;
    c1.color.blue = 0;
    c1.color.alpha = 0xffff;
    c1.c = &c2;

    c2.color.red = 0;
    c2.color.green = 0;
    c2.color.blue = 0xffff;
    c2.color.alpha = 0xffff;
    c2.c = &c1;

    while (1)
    {
	XEvent event;
	struct c *c;

	XNextEvent(display, &event);
	XFindContext(display, event.xany.window, context, (XPointer *)&c);
	switch (event.type)
	{
	case KeyPress:
	    printf("(%d, %d) %d x %d <- (%d, %d) %d x %d\n",
	    c->rect.x, c->rect.y, c->rect.width, c->rect.height,
	    c->c->rect.x, c->c->rect.y, c->c->rect.width, c->c->rect.height);
	    XRenderComposite(display, PictOpSrc, c->c->pict, None, c->pict, 0, 0, 0, 0, 0, 0, c->rect.width, c->rect.height);
	    continue;
	case ButtonPress:
	    break;
	case Expose:
	    XRenderFillRectangle(display, PictOpSrc, c->pict, &c->color, event.xexpose.x, event.xexpose.y, event.xexpose.width, event.xexpose.height);
	    continue;
	case ConfigureNotify:
	    c->rect.x = event.xconfigure.x;
	    c->rect.y = event.xconfigure.y;
	    c->rect.width = event.xconfigure.width;
	    c->rect.height = event.xconfigure.height;
	    continue;
	default:
	    continue;
	}
	break;
    }

    XDestroyWindow(display, window1);
    XDestroyWindow(display, window2);
    XCloseDisplay(display);
    return 0;
}