Add new zero-alpha test to demonstrate (X server?) bug found by Paul Giblock

test/.gitignore

@@ -103,6 +103,7 @@ unantialiased-shapes
 unbounded-operator
 user-data
 xlib-surface
+zero-alpha
 *-out.pdf
 *-out.png
 *-out.ps

test/Makefile.am

@@ -75,7 +75,8 @@ unantialiased-shapes		\
 unbounded-operator		\
 user-data			\
 rel-path                        \
-push-group
+push-group			\
+zero-alpha
 
 # Then we have a collection of tests that are only run if certain
 # features are compiled into cairo

test/zero-alpha.c

@@ -0,0 +1,97 @@
+/*
+ * Copyright © 2006 Red Hat, Inc.
+ *
+ * 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
+ * Red Hat, Inc. not be used in advertising or publicity pertaining to
+ * distribution of the software without specific, written prior
+ * permission. Red Hat, Inc. makes no representations about the
+ * suitability of this software for any purpose.  It is provided "as
+ * is" without express or implied warranty.
+ *
+ * RED HAT, INC. DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS
+ * SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS, IN NO EVENT SHALL RED HAT, INC. 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: Carl D. Worth <cworth@cworth.org>
+ */
+
+#include "cairo-test.h"
+
+#define SIZE 3
+#define REPS 100
+
+/* History:
+ *
+ * 2006-06-13 Paul Giblock reports a "Stange alpha channel problem" on
+ * the cairo mailing list.
+ *
+ * 2006-06-13 Carl Worth writes this test in an attempt to reproduce
+ * the problem. The test first fills in a 3x3 rectangle with red, then
+ * starts pounding on that center pixel with various forms of
+ * zero-alpha rendering to see if its value can ever be made to
+ * change.
+ *
+ * 2006-06-13 Paul Giblock reports that this only happens with the
+ * xlib backend, and then only on some systems.
+ */
+cairo_test_t test = {
+    "zero-alpha",
+    "Testing that drawing with zero alpha has no effect",
+    SIZE, SIZE
+};
+
+static cairo_test_status_t
+draw (cairo_t *cr, int width, int height)
+{
+    int i;
+    cairo_surface_t *surface;
+    uint32_t zero = 0;
+
+    /* First paint background red. */
+    cairo_set_source_rgb (cr, 1.0, 0.0, 0.0); /* red */
+    cairo_paint (cr);
+
+    /* Then we paint zero-alpha in several ways (always REPS times): */
+
+    /* 1. fill a rectangle with a zero-alpha solid source. */
+    cairo_set_source_rgba (cr, 0.0, 0.0, 0.0, 0.0); /* transparent */
+    cairo_rectangle (cr, 1.0, 1.0, 1.0, 1.0);
+    for (i=0; i < REPS; i++)
+	cairo_fill_preserve (cr);
+    cairo_new_path (cr);
+
+    /* 2. paint with a zero-alpha image surface source. */
+    surface = cairo_image_surface_create_for_data ((unsigned char *) &zero,
+						   CAIRO_FORMAT_ARGB32, 1, 1, 4);
+    cairo_set_source_surface (cr, surface, 1, 1);
+    for (i=0; i < REPS; i++)
+	cairo_paint (cr);
+
+    /* 3. clip to rectangle then paint with zero-alpha solid source. */
+    cairo_rectangle (cr, 1.0, 1.0, 1.0, 1.0);
+    cairo_clip (cr);
+    cairo_set_source_rgba (cr, 0.0, 0.0, 0.0, 0.0); /* transparent */
+    for (i=0; i < REPS; i++)
+	cairo_paint (cr);
+
+    /* 4. With the clip still there, paint our image surface. */
+    cairo_set_source_surface (cr, surface, 1, 1);
+    for (i=0; i < REPS; i++)
+	cairo_paint (cr);
+
+    return CAIRO_TEST_SUCCESS;
+}
+
+int
+main (void)
+{
+    return cairo_test (&test, draw);
+}