Remove clip handling from generic surface layer.

Handling clip as part of the surface state, as opposed to being part of
the operation state, is cumbersome and a hindrance to providing true proxy
surface support. For example, the clip must be copied from the surface
onto the fallback image, but this was forgotten causing undue hassle in
each backend. Another example is the contortion the meta surface
endures to ensure the clip is correctly recorded. By contrast passing the
clip along with the operation is quite simple and enables us to write
generic handlers for providing surface wrappers. (And in the future, we
should be able to write more esoteric wrappers, e.g. automatic 2x FSAA,
trivially.)

In brief, instead of the surface automatically applying the clip before
calling the backend, the backend can call into a generic helper to apply
clipping. For raster surfaces, clip regions are handled automatically as
part of the composite interface. For vector surfaces, a clip helper is
introduced to replay and callback into an intersect_clip_path() function
as necessary.

Whilst this is not primarily a performance related change (the change
should just move the computation of the clip from the moment it is applied
by the user to the moment it is required by the backend), it is important
to track any potential regression:

ppc:
Speedups
========
image-rgba         evolution-20090607-0    1026085.22 0.18% -> 672972.07 0.77%:  1.52x speedup
▌
image-rgba         evolution-20090618-0    680579.98 0.12% -> 573237.66  0.16%:  1.19x speedup
▎
image-rgba      swfdec-fill-rate-4xaa-0    460296.92 0.36% -> 407464.63  0.42%:  1.13x speedup
▏
image-rgba      swfdec-fill-rate-2xaa-0    128431.95 0.47% -> 115051.86  0.42%:  1.12x speedup
▏
Slowdowns
=========
image-rgba     firefox-periodic-table-0    56837.61 0.78% -> 66055.17    3.20%:  1.09x slowdown
▏

1 files changed, 138 insertions, 0 deletions

diff --git a/src/cairo-surface-clipper.c b/src/cairo-surface-clipper.c
new file mode 100644
index 000000000..d536f0cbe
--- /dev/null
+++ b/src/cairo-surface-clipper.c
@@ -0,0 +1,138 @@
+/* cairo - a vector graphics library with display and print output
+ *
+ * Copyright © 2009 Chris Wilson
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it either under the terms of the GNU Lesser General Public
+ * License version 2.1 as published by the Free Software Foundation
+ * (the "LGPL") or, at your option, under the terms of the Mozilla
+ * Public License Version 1.1 (the "MPL"). If you do not alter this
+ * notice, a recipient may use your version of this file under either
+ * the MPL or the LGPL.
+ *
+ * You should have received a copy of the LGPL along with this library
+ * in the file COPYING-LGPL-2.1; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+ * You should have received a copy of the MPL along with this library
+ * in the file COPYING-MPL-1.1
+ *
+ * The contents of this file are subject to the Mozilla Public License
+ * Version 1.1 (the "License"); you may not use this file except in
+ * compliance with the License. You may obtain a copy of the License at
+ * http://www.mozilla.org/MPL/
+ *
+ * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY
+ * OF ANY KIND, either express or implied. See the LGPL or the MPL for
+ * the specific language governing rights and limitations.
+ *
+ * The Original Code is the cairo graphics library.
+ *
+ * The Initial Developer of the Original Code is Red Hat, Inc.
+ *
+ * Contributor(s):
+ *      Chris Wilson <chris@chris-wilson.co.uk>
+ */
+
+#include "cairoint.h"
+
+#include "cairo-surface-clipper-private.h"
+
+/* A collection of routines to facilitate vector surface clipping */
+
+static cairo_status_t
+_cairo_surface_clipper_intersect_clip_path_recursive (cairo_surface_clipper_t *clipper,
+						      cairo_clip_path_t *clip_path)
+{
+    cairo_status_t status;
+
+    if (clip_path->prev != NULL) {
+	status =
+	    _cairo_surface_clipper_intersect_clip_path_recursive (clipper,
+								  clip_path->prev);
+	if (unlikely (status))
+	    return status;
+    }
+
+    return clipper->intersect_clip_path (clipper,
+					 &clip_path->path,
+					 clip_path->fill_rule,
+					 clip_path->tolerance,
+					 clip_path->antialias);
+}
+
+cairo_status_t
+_cairo_surface_clipper_set_clip (cairo_surface_clipper_t *clipper,
+				 cairo_clip_t *clip)
+{
+    cairo_status_t status;
+    cairo_bool_t clear;
+
+    /* XXX as we cache a reference to the path, and compare every time,
+     * we may in future need to install a notification if the clip->path
+     * is every modified (e.g. cairo_clip_translate).
+     */
+
+    if (clip == NULL && clipper->clip.path == NULL)
+	return CAIRO_STATUS_SUCCESS;
+
+    if (clip != NULL && clip->path == clipper->clip.path)
+	return CAIRO_STATUS_SUCCESS;
+
+    if (clip != NULL && clipper->clip.path != NULL &&
+	_cairo_path_fixed_equal (&clip->path->path, &clipper->clip.path->path))
+    {
+	return CAIRO_STATUS_SUCCESS;
+    }
+
+    /* all clipped out state should never propagate this far */
+    assert (clip == NULL || clip->path != NULL);
+
+    /* Check whether this clip is a continuation of the previous.
+     * If not, we have to remove the current clip and rebuild.
+     */
+    clear = clip == NULL || clip->path->prev != clipper->clip.path;
+
+    _cairo_clip_reset (&clipper->clip);
+    _cairo_clip_init_copy (&clipper->clip, clip);
+
+    if (clear) {
+	clipper->is_clipped = FALSE;
+	status = clipper->intersect_clip_path (clipper, NULL, 0, 0, 0);
+	if (unlikely (status))
+	    return status;
+
+	if (clip != NULL && clip->path != NULL) {
+	    status =
+		_cairo_surface_clipper_intersect_clip_path_recursive (clipper,
+								      clip->path);
+	    clipper->is_clipped = TRUE;
+	}
+    } else {
+	cairo_clip_path_t *path = clip->path;
+
+	clipper->is_clipped = TRUE;
+	status = clipper->intersect_clip_path (clipper,
+					       &path->path,
+					       path->fill_rule,
+					       path->tolerance,
+					       path->antialias);
+    }
+
+    return status;
+}
+
+void
+_cairo_surface_clipper_init (cairo_surface_clipper_t *clipper,
+			     cairo_surface_clipper_intersect_clip_path_func_t func)
+{
+    _cairo_clip_init (&clipper->clip);
+    clipper->is_clipped = FALSE;
+    clipper->intersect_clip_path = func;
+}
+
+void
+_cairo_surface_clipper_reset (cairo_surface_clipper_t *clipper)
+{
+    _cairo_clip_reset (&clipper->clip);
+    clipper->is_clipped = FALSE;
+}