[test] Add a test case to question the mutability of sources.

Are patterns mutable? The image backend is quite happy to write and read
from the same surface, whereas the vector targets create snapshots... This
test case exploits that inconsistency.

Also the interested reader will note that not only does this demonstrate
translational invariance, but a discrepancy with similar surfaces.

test/.gitignore

@@ -182,6 +182,7 @@ scale-source-surface-paint
 select-font-face
 select-font-no-show-text
 self-copy
+self-copy-overlap
 self-intersecting
 set-source
 show-glyphs-many

test/Makefile.am

@@ -138,6 +138,7 @@ stroke-image$(EXEEXT)				        \
 select-font-face$(EXEEXT)				\
 select-font-no-show-text$(EXEEXT)			\
 self-copy$(EXEEXT)					\
+self-copy-overlap$(EXEEXT)				\
 self-intersecting$(EXEEXT)				\
 set-source$(EXEEXT)					\
 show-text-current-point$(EXEEXT)			\
@@ -640,6 +641,8 @@ REFERENCE_IMAGES = \
 	select-font-face-quartz-ref.png \
 	self-copy-ref.png	\
 	self-copy-ps-ref.png	\
+	self-copy-overlap-ref.png	\
+	self-copy-overlap-rgb24-ref.png	\
 	self-intersecting-ref.png	\
 	self-intersecting-rgb24-ref.png	\
 	set-source-ref.png	\

test/self-copy-overlap.c

@@ -0,0 +1,56 @@
+/*
+ * Copyright 2008 Chris Wilson
+ *
+ * Permission to use, copy, modify, distribute, and sell this software
+ * and its documentation for any purpose is hereby granted without
+ * fee, provided that the above copyright notice appear in all copies
+ * and that both that copyright notice and this permission notice
+ * appear in supporting documentation, and that the name of
+ * Chris Wilson not be used in advertising or publicity pertaining to
+ * distribution of the software without specific, written prior
+ * permission. Chris Wilson makes no representations about the
+ * suitability of this software for any purpose.  It is provided "as
+ * is" without express or implied warranty.
+ *
+ * CHRIS WILSON DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS
+ * SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS, IN NO EVENT SHALL CHRIS WILSON BE LIABLE FOR ANY SPECIAL,
+ * INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER
+ * RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
+ * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR
+ * IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ *
+ * Author: Chris Wilson <chris@chris-wilson.co.uk>
+ */
+
+/* Question: are patterns mutable? The answer depends on who you ask... */
+
+#include "cairo-test.h"
+
+static cairo_test_draw_function_t draw;
+
+/* This test is only interesting if the target has alpha */
+static const cairo_test_t test = {
+    "self-copy-overlap",
+    "Tests painting to itself using itself as the source",
+    200, 200,
+    draw
+};
+
+static cairo_test_status_t
+draw (cairo_t *cr, int width, int height)
+{
+    cairo_set_source_rgba (cr, 0, 0, 0, .01);
+    cairo_paint (cr);
+
+    cairo_set_source_surface (cr, cairo_get_target (cr), 1, 1);
+    cairo_paint (cr);
+
+    return CAIRO_TEST_SUCCESS;
+}
+
+int
+main (void)
+{
+    return cairo_test (&test);
+}