visible window rectangle in pixmap redirection

[Tim Janik <timj imendio com>]

hi Alex.

it'd be great if you could take a look at my latest comment on the
offscreen windows bug report, i.e.:
  http://bugzilla.gnome.org/show_bug.cgi?id=318807#c48

it adresses just the pixmap redirection portions that you split off
some while ago and lists remaining issues that need solving before
inclusion.
in particular, i'd like to know:

- gtk_widget_get_snapshot() is supposed to snapshot whole widgets
  (i.e. all of widget->allocation.width/height).
  so why is gdk_window_end_paint() calling
  _gdk_window_calculate_full_clip_region() (indirectly via
  setup_redirect_clip()) to constrain the redirected area
  to the visible widget area?

- why is _gdk_windowing_window_get_visible_rect() a backend specific
  function? couldn't we get the visible rectangle of a window from
  window->parent->width/height and window->x/y?

- i'm wondering if there is a use case at all for snapshooting *only*
  the visible area of a widget. i think the semantics of
  gtk_widget_get_snapshot() are fine if it snapshoots all of a widgets
  allocation, and i'd like to get rid of all the clip-to-visible-rect
  logic. if there is indeed a use case for snapshoting only the
  visible portion of a widget (afaics relevant in scrolled window
  contexts only), we should be able to simply provide:
    void gtk_widget_get_visible_rect (Widget*, Rect*);
  that provides coordinates for use with gtk_widget_get_snapshot().

thanks for the patch in the first place. i think the above are the last
major issues left before pixmap redirection can go in.

---
ciaoTJ