[cairo] cairo_surface_write_to_png and 32-bit visuals in 1.10.0

[Ross Alexander]

After looking at this problem some more, specially in the setup of XCB surfaces I noticed if cairo is passed a 32bit visual it effectively assumes it is 24bit by setting alpha_masks = 0 before getting the pixman format, resulting in a 24 bit x8r8g8b8 format.  It then gets the xrender format which is a 32bit format but there doesn't seem to be a simple way of getting from the xrender format back to the correct pixman format.  I've just hacked a simple chance which works may well not be the way forward.

*** cairo-xcb-surface.c.orig	2010-10-06 09:13:36.000000000 +0100
--- cairo-xcb-surface.c	2010-10-06 09:14:30.000000000 +0100
***************
*** 1179,1184 ****
--- 1179,1186 ----
      image_masks.red_mask   = visual->red_mask;
      image_masks.green_mask = visual->green_mask;
      image_masks.blue_mask  = visual->blue_mask;
+     if (depth == 32)
+         image_masks.alpha_mask = 0xffffffff & (~visual->red_mask) & (~visual->green_mask) & (~visual->blue_mask);
      if (depth > 16)
  	image_masks.bpp = 32;
      else if (depth > 8)

Cheers,
Ross


> 
> #ifdef XLIB
>   cairo_surface_t *surface = cairo_xlib_surface_create(dpy, 
> target_win, vinfos[0].visual, geom->width, geom->height); #else
>   cairo_surface_t *surface = cairo_xcb_surface_create(conn, 
> target_win, v, geom->width, geom->height); #endif
>   free(geom);
>   cairo_surface_write_to_png(surface, file);
> 
> This works fine for 24-bit visual windows but with 32-bit visuals (eg gnome-terminal) I get the following error.
> 
> xwd: cairo-xcb-surface.c:504: _get_image: Assertion `reply->depth == surface->depth' failed.
> 
> Using xlib on 32-bit visuals doesn’t fail but instead produces a zero sized PNG file.


--
Chris Wilson, Intel Open Source Technology Centre


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