Add self-intersecting test which demonstrates the long-standing bug with stroking self-intersecting paths.

ChangeLog

@@ -1,3 +1,12 @@
+2005-06-01  Carl Worth  <cworth@cworth.org>
+
+	* test/.cvsignore:
+	* test/Makefile.am:
+	* test/self-intersecting-ref.png:
+	* test/self-intersecting.c: (draw), (main): Add self-intersecting
+	test which demonstrates the long-standing bug with stroking
+	self-intersecting paths.
+
 2005-06-01  Carl Worth  <cworth@cworth.org>
 
 	* src/cairo-gstate.c (_cairo_gstate_get_clip_extents): Fix bug in

test/.cvsignore

@@ -29,6 +29,7 @@ rel-path
 scale-source-surface-paint
 select-font-no-show-text
 self-copy
+self-intersecting
 set-source
 source-clip
 source-surface-scale-paint

test/Makefile.am

@@ -20,6 +20,7 @@ pixman-rotate			\
 scale-source-surface-paint	\
 select-font-no-show-text	\
 self-copy			\
+self-intersecting		\
 set-source			\
 source-clip			\
 source-surface-scale-paint	\
@@ -67,6 +68,7 @@ path-data-ref.png			\
 pixman-rotate-ref.png			\
 romedalen.png				\
 self-copy-ref.png			\
+self-intersecting-ref.png		\
 scale-source-surface-paint-ref.png	\
 set-source-ref.png			\
 source-clip-ref.png			\
@@ -145,6 +147,7 @@ pixman_rotate_LDADD = $(LDADDS)
 scale_source_surface_paint_LDADD = $(LDADDS)
 select_font_no_show_text_LDADD = $(LDADDS)
 self_copy_LDADD = $(LDADDS)
+self_intersecting_LDADD = $(LDADDS)
 set_source_LDADD = $(LDADDS)
 source_clip_LDADD = $(LDADDS)
 source_surface_scale_paint_LDADD = $(LDADDS)

test/self-intersecting.c

@@ -0,0 +1,89 @@
+/*
+ * Copyright © 2005 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>
+ */
+
+/* Bug history
+ *
+ * 2005-06-01  Carl Worth  <cworth@cworth.org>
+ *
+ *   There's a long-standing bug in that self-intersecting paths give
+ *   an incorrect result when stroked. The problem is that the
+ *   trapezoids are generated incrementally along the stroke and as
+ *   such, are not disjoint. The errant intersections of these
+ *   trapezoids then leads to overfilled pixels.
+ *
+ *   The test belows first creates and fills a path. Then it creates a
+ *   second path which has a stroked boundary identical to the first
+ *   filled path. But the results of the two operations are
+ *   different. The most obvious difference is in the central region
+ *   where the entire path intersects itself. But notice that every
+ *   time the path turns there are also errors on the inside of the
+ *   turn, (since the subsequent trapezoids along the path intersect).
+ */
+
+#include "cairo-test.h"
+
+cairo_test_t test = {
+    "self-intersecting",
+    "Test strokes of self-intersecting paths",
+    10, 20
+};
+
+static cairo_test_status_t
+draw (cairo_t *cr, int width, int height)
+{
+    cairo_translate (cr, 1.0, 1.0);
+
+    cairo_set_source_rgb (cr, 1, 0, 0); /* red */
+
+    /* First draw the desired shape with a fill */
+    cairo_rectangle (cr, 0.5, 0.5,  4.0, 4.0);
+    cairo_rectangle (cr, 3.5, 3.5,  4.0, 4.0);
+    cairo_rectangle (cr, 3.5, 1.5, -2.0, 2.0);
+    cairo_rectangle (cr, 6.5, 4.5, -2.0, 2.0);
+
+    cairo_fill (cr);
+
+    /* Then try the same thing with a stroke */
+    cairo_translate (cr, 0, 10);
+    cairo_move_to (cr, 1.0, 1.0);
+    cairo_rel_line_to (cr,  3.0,  0.0);
+    cairo_rel_line_to (cr,  0.0,  6.0);
+    cairo_rel_line_to (cr,  3.0,  0.0);
+    cairo_rel_line_to (cr,  0.0, -3.0);
+    cairo_rel_line_to (cr, -6.0,  0.0);
+    cairo_close_path (cr);
+
+    cairo_set_line_width (cr, 1.0);
+    cairo_stroke (cr);
+
+    return CAIRO_TEST_SUCCESS;
+}
+
+int
+main (void)
+{
+    return cairo_test_expect_failure (&test, draw,
+    "Self-intersecting strokes are wrong due to incremental trapezoidization.");
+}