Add new skew-extreme test case.

This test currently fails, demonstrating the bug reported here:

	Skew transforms were broken by the cairo update in December
	https://bugzilla.mozilla.org/show_bug.cgi?id=373632

test/.gitignore

@@ -121,6 +121,7 @@ self-intersecting
 set-source
 show-glyphs-many
 show-text-current-point
+skew-extreme
 source-clip
 source-clip-scale
 source-surface-scale-paint

test/Makefile.am

@@ -85,6 +85,7 @@ self-copy			\
 self-intersecting		\
 set-source			\
 show-text-current-point		\
+skew-extreme			\
 source-clip			\
 source-clip-scale		\
 source-surface-scale-paint	\

test/skew-extreme.c

@@ -0,0 +1,126 @@
+/*
+ * Copyright © 2007 Red Hat, Inc.
+ *
+ * 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: Carl Worth <cworth@cworth.org>
+ */
+
+#include "cairo-test.h"
+
+/* This test case is designed to exercise the following bug:
+ *
+ *	Skew transforms were broken by the cairo update in December
+ *	https://bugzilla.mozilla.org/show_bug.cgi?id=373632
+ *
+ * What's happening is that the rectangle is being skewed into the
+ * following shape:
+ *
+ * a__b
+ *  \ \
+ *   \ \
+ *    \ \
+ *     \ \
+ *      \ \
+ *      d\_\c
+ *
+ * and the bug is that _cairo_traps_tessellate_convex_quad is
+ * comparing b.x as less then d.x and therfore determining that the bc
+ * edge is left of the ad edge. The fix is simply to compare c.x to
+ * d.x instead of b.x to d.x .
+ */
+
+#define PAD		2
+#define LINE_WIDTH	10
+#define LINE_LENGTH	(2 * LINE_WIDTH)
+#define SKEW_FACTOR	5.0
+#define WIDTH		(PAD + (LINE_LENGTH * SKEW_FACTOR) + LINE_WIDTH + PAD)
+#define HEIGHT		(PAD + LINE_WIDTH + (LINE_LENGTH * SKEW_FACTOR) + LINE_WIDTH + PAD)
+
+static cairo_test_draw_function_t draw;
+
+cairo_test_t test = {
+    "skew-extreme",
+    "Test cases of extreme skew.",
+    WIDTH, HEIGHT,
+    draw
+};
+
+static cairo_test_status_t
+draw (cairo_t *cr, int width, int height)
+{
+    /* We draw in the default black, so paint white first. */
+    cairo_save (cr);
+    cairo_set_source_rgb (cr, 1.0, 1.0, 1.0); /* white */
+    cairo_paint (cr);
+    cairo_restore (cr);
+
+    cairo_translate (cr, PAD, PAD);
+
+    cairo_set_line_width (cr, LINE_WIDTH);
+    cairo_set_line_cap (cr, CAIRO_LINE_CAP_BUTT);
+
+    cairo_save (cr);
+    {
+	cairo_matrix_t skew_x = {
+	    1.0, 0.0,
+	    SKEW_FACTOR, 1.0,
+	    0.0, 0.0
+	};
+
+	cairo_translate (cr, LINE_WIDTH / 2.0, 0.0);
+
+	cairo_transform (cr, &skew_x);
+
+	cairo_move_to (cr, 0.0, 0.0);
+	cairo_line_to (cr, 0.0, LINE_LENGTH);
+	cairo_stroke (cr);
+    }
+    cairo_restore (cr);
+
+    cairo_translate (cr, 0.0, LINE_WIDTH);
+
+    cairo_save (cr);
+    {
+	cairo_matrix_t skew_y = {
+	    1.0, SKEW_FACTOR,
+	    0.0, 1.0,
+	    0.0, 0.0
+	};
+
+	cairo_translate (cr, 0.0, LINE_WIDTH / 2.0);
+
+	cairo_transform (cr, &skew_y);
+
+	cairo_move_to (cr, 0.0, 0.0);
+	cairo_line_to (cr, LINE_LENGTH, 0.0);
+	cairo_stroke (cr);
+    }
+    cairo_restore (cr);
+
+    return CAIRO_TEST_SUCCESS;
+}
+
+int
+main (void)
+{
+    return cairo_test (&test);
+}