test: check for tessellator regression from missed stop events

The new tessellator contains a regression where stop events
that aren't followed by start events sometimes cause the
trapezoid to the left of an edge to be too high.

1 files changed, 89 insertions, 0 deletions

diff --git a/test/fill-missed-stop.c b/test/fill-missed-stop.c
new file mode 100644
index 000000000..cdf9ba566
--- /dev/null
+++ b/test/fill-missed-stop.c
@@ -0,0 +1,89 @@
+/*
+ * Copyright © 2006 M Joonas Pihlaja
+ *
+ * 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 Joonas Pihlaja
+ * not be used in advertising or publicity pertaining to distribution
+ * of the software without specific, written prior permission.
+ * Joonas Pihlaja makes no representations about the suitability of this
+ * software for any purpose.  It is provided "as is" without express
+ * or implied warranty.
+ *
+ * JOONAS PIHLAJA DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
+ * INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN
+ * NO EVENT SHALL JOONAS PIHLAJA 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: M Joonas Pihlaja <jpihlaja@cc.helsinki.fi>
+ */
+
+/* Bug history
+ *
+ * 2006-12-05  M Joonas Pihlaja <jpihlaja@cc.helsinki.fi>
+ *
+ *  The tessellator has a regression where a trapezoid may continue
+ *  below the end of a polygon edge (i.e. the bottom of the trapezoid
+ *  is miscomputed.)  This can only happen if the right edge of a
+ *  trapezoid stops earlier than the left edge and there is no start
+ *  event at the end point of the right edge.
+ */
+
+#include "cairo-test.h"
+
+static cairo_test_draw_function_t draw;
+#define SIZE 50
+
+cairo_test_t test = {
+    "fill-missed-stop",
+    "Tests that the tessellator doesn't miss stop events when generating trapezoids",
+    SIZE+3, SIZE+3,
+    draw
+};
+
+static cairo_test_status_t
+draw (cairo_t *cr, int width, int height)
+{
+    cairo_set_source_rgb (cr, 1, 0, 0);
+
+    cairo_translate (cr, 1, 1);
+
+    /* What it should look like, with # marking the filled areas:
+     *
+     * |\    |\
+     * |#\   |#\
+     * |##\__|##\
+     *     \#|
+     *      \|
+     *
+     * What it looke like with the bug, when the rightmost edge's end
+     * is missed:
+     *
+     * |\    |\
+     * |#\   |#\
+     * |##\__|##\
+     *     \#####|
+     *      \####|
+     */
+
+    cairo_move_to (cr, 0, 0);
+    cairo_line_to (cr, SIZE/2, SIZE);
+    cairo_line_to (cr, SIZE/2, 0);
+    cairo_line_to (cr, SIZE, SIZE/2);
+    cairo_line_to (cr, 0, SIZE/2);
+    cairo_close_path (cr);
+    cairo_fill (cr);
+
+    return CAIRO_TEST_SUCCESS;
+}
+
+int
+main (void)
+{
+    return cairo_test (&test);
+}