test: tessellator event comparator test case for degenerate edges.

There's currently a regression bug in the tessellation code from
switching to the new tessellator.  The bug is caused by
confusion in the comparator used to order events when there are
degenerate edges.  This test is derived from the zrusin-another
performance test case.

test/Makefile.am

@@ -32,6 +32,7 @@ extend-reflect			\
 fill-and-stroke			\
 fill-and-stroke-alpha		\
 fill-and-stroke-alpha-add	\
+fill-degenerate-sort-order	\
 fill-rule			\
 filter-nearest-offset		\
 font-face-get-type		\
@@ -216,6 +217,8 @@ fill-and-stroke-ps-argb32-ref.png			\
 fill-and-stroke-alpha-ref.png				\
 fill-and-stroke-alpha-svg-ref.png			\
 fill-and-stroke-alpha-add-ref.png			\
+fill-degenerate-sort-order-ref.png			\
+fill-degenerate-sort-order-rgb24-ref.png		\
 fill-rule-ref.png					\
 fill-rule-rgb24-ref.png					\
 fill-rule-ps-argb32-ref.png				\

test/fill-degenerate-sort-order.c

@@ -0,0 +1,110 @@
+/*
+ * 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>
+ *
+ *   There's currently a regression bug in the tessellation code from
+ *   switching to the "new tessellator".  The bug is caused by
+ *   confusion in the comparator used to order events when there are
+ *   degenerate edges.
+ */
+
+#include "cairo-test.h"
+
+static cairo_test_draw_function_t draw;
+
+cairo_test_t test = {
+    "fill-degenerate-sort-order",
+    "Tests the tessellator's event comparator with degenerate input",
+    190, 120,
+    draw
+};
+
+/* Derived from zrusin's "another" polygon in the performance suite. */
+static cairo_test_status_t
+draw (cairo_t *cr_orig, int width, int height)
+{
+    /* XXX: I wanted to be able to simply fill the nasty path to the
+     * surface and then use a reference image to catch bugs, but the
+     * renderer used when testing the postscript backend gets the
+     * degeneracy wrong, thus leading to an (unfixable?) test case
+     * failure.  Are external renderer bugs our bugs too?  Instead,
+     * tessellate the polygon and render to the surface the results of
+     * point sampling the tessellated path.  If there would be a way
+     * to XFAIL only some backends we could do that for the .ps
+     * backend only. */
+    int x,y;
+    int sample_stride;
+    cairo_surface_t *surf = cairo_image_surface_create (CAIRO_FORMAT_ARGB32, width, height);
+    cairo_t *cr = cairo_create (surf);
+    cairo_set_source_rgb (cr_orig, 1, 0, 0);
+
+    /* The polygon uses (43,103) as its "base point".  Closed
+     * subpaths are simulated by going from the base point to the
+     * subpath's first point, doing the subpath, and returning to the
+     * base point.  The moving to and from the base point causes
+     * degenerate edges which shouldn't result in anything visible. */
+    cairo_move_to (cr, 43, 103);
+
+    /* First subpath. */
+    cairo_line_to (cr, 91, 101);
+    cairo_line_to (cr, 0, 112);
+    cairo_line_to (cr, 60, 0);
+    cairo_line_to (cr, 91, 101);
+
+    cairo_line_to (cr, 43, 103);
+
+    /* Second subpath. */
+    cairo_line_to (cr, 176, 110);
+    cairo_line_to (cr, 116, 100);
+    cairo_line_to (cr, 176, 0);
+    cairo_line_to (cr, 176, 110);
+
+    cairo_close_path (cr);
+
+    /* Point sample the tessellated path. The x and y starting offsets
+     * are chosen to hit the nasty bits while still being able to do a
+     * relatively sparse sampling. */
+    sample_stride = 4;
+    for (y = 0; y < height; y += sample_stride) {
+	for (x = 0; x < width; x += sample_stride) {
+	    if (cairo_in_fill (cr, x, y)) {
+		cairo_rectangle(cr_orig, x, y, sample_stride, sample_stride);
+		cairo_fill (cr_orig);
+	    }
+	}
+    }
+    cairo_destroy (cr);
+    cairo_surface_destroy (surf);
+    return CAIRO_TEST_SUCCESS;
+}
+
+int
+main (void)
+{
+    return cairo_test (&test);
+}