test: Add an example of seams.

A pair of perfectly conjoint quads should not produce a seam when
accumulating into a temporary mask. Yet here is an example of where they
do!

test/Makefile.am

@@ -166,6 +166,9 @@ REFERENCE_IMAGES = \
 	bug-bo-rectangular.ref.png \
 	bug-bo-rectangular.image16.ref.png \
 	bug-bo-rectangular.ps.xfail.png \
+	bug-seams.ref.png \
+	bug-seams.xlib.ref.png \
+	bug-seams.xlib-fallback.ref.png \
 	bilevel-image.ref.png \
 	bitmap-font.ref.png \
 	bitmap-font.rgb24.ref.png \

test/Makefile.sources

@@ -12,6 +12,7 @@ test_sources = \
 	big-trap.c					\
 	bilevel-image.c					\
 	bug-bo-rectangular.c				\
+	bug-seams.c					\
 	caps.c						\
 	caps-joins.c					\
 	caps-joins-alpha.c				\

test/bug-seams.c

@@ -0,0 +1,98 @@
+/*
+ * Copyright 2010 Soeren Sandmann Petersen
+ *
+ * Permission is hereby granted, free of charge, to any person
+ * obtaining a copy of this software and associated documentation
+ * files (the "Software"), to deal in the Software without
+ * restriction, including without limitation the rights to use, copy,
+ * modify, merge, publish, distribute, sublicense, and/or sell copies
+ * of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+ * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+ * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ *
+ * Author: Soeren Sandmann <sandmann@daimi.au.dk>
+ */
+
+/* Exercises a case of seam appearing between two polygons in the image
+ * backend but not in xlib [using pixman].
+ */
+
+#include "cairo-test.h"
+
+static void
+draw_quad (cairo_t *cr,
+	   double x1, double y1, double x2, double y2,
+	   double x3, double y3, double x4, double y4)
+{
+    cairo_move_to (cr, x1, y1);
+    cairo_line_to (cr, x2, y2);
+    cairo_line_to (cr, x3, y3);
+    cairo_line_to (cr, x4, y4);
+    cairo_close_path (cr);
+}
+
+static cairo_test_status_t
+draw (cairo_t *cr, int width, int height)
+{
+    cairo_set_source_rgb (cr, 0, 0, 0);
+    cairo_paint (cr);
+
+    cairo_scale (cr, 20, 20);
+    cairo_translate (cr, 5, 1);
+
+    cairo_push_group (cr);
+    cairo_set_operator (cr, CAIRO_OPERATOR_ADD);
+
+    cairo_set_source_rgb (cr, 0, 0.6, 0);
+    draw_quad (cr,
+	       1.50, 1.50,
+	       2.64, 1.63,
+	       1.75, 2.75,
+	       0.55, 2.63);
+    cairo_fill (cr);
+    draw_quad (cr,
+	       0.55, 2.63,
+	       1.75, 2.75,
+	       0.98, 4.11,
+	       -0.35, 4.05);
+    cairo_fill (cr);
+
+    cairo_pop_group_to_source (cr);
+    cairo_set_operator (cr, CAIRO_OPERATOR_OVER);
+    cairo_paint (cr);
+
+    cairo_translate (cr, 10, 0);
+
+    cairo_set_source_rgb (cr, 0, 0.6, 0);
+    draw_quad (cr,
+	       1.50, 1.50,
+	       2.64, 1.63,
+	       1.75, 2.75,
+	       0.55, 2.63);
+    draw_quad (cr,
+	       0.55, 2.63,
+	       1.75, 2.75,
+	       0.98, 4.11,
+	       -0.35, 4.05);
+    cairo_fill (cr);
+
+    return CAIRO_TEST_SUCCESS;
+}
+
+CAIRO_TEST (bug_seams,
+	    "Check the fidelity of the rasterisation.",
+	    "raster", /* keywords */
+	    "target=raster", /* requirements */
+	    500, 300,
+	    NULL, draw)