test: check if cairo_in_fill() is reporting false positives for empty trapezoids.

cairo_in_fill() may report true if a query point lands on an edge of an
empty trapezoid.

test/Makefile.am

@@ -44,6 +44,7 @@ get-group-target		\
 get-path-extents                \
 gradient-alpha			\
 infinite-join			\
+in-fill-empty-trapezoid		\
 leaky-dash			\
 leaky-polygon			\
 line-width			\
@@ -238,6 +239,8 @@ glyph-cache-pressure-ps-argb32-ref.png			\
 glyph-cache-pressure-svg-ref.png			\
 gradient-alpha-ref.png					\
 gradient-alpha-rgb24-ref.png				\
+in-fill-empty-trapezoid-ref.png				\
+in-fill-empty-trapezoid-rgb24-ref.png			\
 infinite-join-ref.png					\
 infinite-join-ps-argb32-ref.png				\
 leaky-dash-ref.png					\

test/in-fill-empty-trapezoid.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 cairo_in_fill () function can sometimes produce false
+ *  positives when the tessellator produces empty trapezoids
+ *  and the query point lands exactly on a trapezoid edge.
+ */
+
+#include "cairo-test.h"
+
+static cairo_test_draw_function_t draw;
+
+cairo_test_t test = {
+    "in-fill-empty-trapezoid",
+    "Tests that the tessellator doesn't produce obviously empty trapezoids",
+    10, 10,
+    draw
+};
+
+static cairo_test_status_t
+draw (cairo_t *cr_orig, int width, int height)
+{
+    int x,y;
+    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);
+
+    /* Empty horizontal trapezoid. */
+    cairo_move_to (cr, 0, height/3);
+    cairo_line_to (cr, width, height/3);
+    cairo_close_path (cr);
+
+    /* Empty non-horizontal trapezoid #1. */
+    cairo_move_to (cr, 0, 0);
+    cairo_line_to (cr, width, height/2);
+    cairo_close_path (cr);
+
+    /* Empty non-horizontal trapezoid #2 intersecting #1. */
+    cairo_move_to (cr, 0, height/2);
+    cairo_line_to (cr, width, 0);
+    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. */
+    for (y = 0; y < height; y++) {
+	for (x = 0; x < width; x++) {
+	    if (cairo_in_fill (cr, x, y)) {
+		cairo_rectangle(cr_orig, x, y, 1, 1);
+		cairo_fill (cr_orig);
+	    }
+	}
+    }
+    cairo_destroy (cr);
+    cairo_surface_destroy (surf);
+    return CAIRO_TEST_SUCCESS;
+}
+
+int
+main (void)
+{
+    return cairo_test (&test);
+}