/* gcc -o test test.c -Wall -g `pkg-config --cflags --libs x11 cairo-xlib` */

#include <stdlib.h>
#include <stdio.h>
#include <X11/Xlib.h>
#include <X11/Xutil.h>
#include <X11/extensions/Xrender.h>
#include <cairo-xlib.h>

static Visual
*findArgbVisual (Display *d)
{
    int                 screen = DefaultScreen (d);
    XVisualInfo		*xvi;
    XVisualInfo		temp;
    int			nvi;
    int			i;
    XRenderPictFormat	*format;
    Visual		*visual;

    temp.screen  = screen;
    temp.depth   = 32;
    temp.class = TrueColor;

    xvi = XGetVisualInfo (d,
			  VisualScreenMask |
			  VisualDepthMask  |
			  VisualClassMask,
			  &temp,
			  &nvi);
    if (!xvi)
	return 0;

    visual = 0;
    for (i = 0; i < nvi; i++)
    {
	format = XRenderFindVisualFormat (d, xvi[i].visual);
	if (format->type == PictTypeDirect && format->direct.alphaMask)
	{
	    visual = xvi[i].visual;
	    break;
	}
    }

    XFree (xvi);

    return visual;
}

int
main (int argc, char **argv)
{
    Display *d;
    Visual *v;
    XWindowAttributes wa;
    Window w, w2;
    cairo_surface_t *s, *s2;
    cairo_t *cr;

    d = XOpenDisplay(NULL);
	if(!d) return 1;

    v = findArgbVisual (d);
        if(!v) abort ();
    XSetWindowAttributes attr = {};
    attr.background_pixel = 0;
    attr.border_pixel     = 0;
    attr.colormap	  = XCreateColormap (d, RootWindow(d, 0),
    					     v, AllocNone);

    w = XCreateWindow(d, RootWindow(d, 0), 0, 0, 1024, 768, 0,
                            32, InputOutput, v, CWBackPixel | CWBorderPixel | CWColormap, &attr);
    XMapWindow (d, w);
    s = cairo_xlib_surface_create (d, w, v, 1024, 768);
    cr = cairo_create (s);

    w2 = XCreateSimpleWindow (d, RootWindow(d, 0), 0, 0, 400, 400, 0, 0, 1234567);
    XMapWindow (d, w2);
    XGetWindowAttributes(d, w2, &wa);
    s2 = cairo_xlib_surface_create (d, w2, wa.visual, wa.width, wa.height);

    XFlush (d);
    XSync (d, w);

    cairo_save (cr);
    cairo_set_source_rgba (cr, 1.0, 0.0, 0.0, 0.5);
    cairo_set_operator (cr, CAIRO_OPERATOR_SOURCE);
    cairo_paint (cr);
    cairo_restore (cr);

    cairo_matrix_t m;
    m.xx = m.yy = 2.0; /* XXX 1.0 doesn't crash xserver XXX */
    m.xy = m.yx = 0.0;
    m.x0 = m.y0 = 0.0;
    cairo_pattern_t *p = cairo_pattern_create_for_surface (s2);
    cairo_pattern_set_matrix (p, &m);
    cairo_set_source (cr, p);
    cairo_paint (cr);
    cairo_pattern_destroy (p);

    XFlush (d);
    XSync (d, w);
    
    return 0;
}