Add degenerate-pen test case.

This demonstrates the assertion failure pointed out by
Benjamin Otte here:

	[cairo] Assertion 'i < pen->num_vertices' failed in 1.4.10
	http://lists.cairographics.org/archives/cairo/2007-August/011282.html

test/.gitignore

@@ -36,6 +36,7 @@ dash-scale
 dash-state
 dash-zero-length
 degenerate-path
+degenerate-pen
 device-offset
 device-offset-positive
 extend-pad

test/Makefile.am

@@ -29,6 +29,7 @@ dash-scale			\
 dash-zero-length		\
 dash-state			\
 degenerate-path			\
+degenerate-pen			\
 device-offset			\
 device-offset-positive		\
 extend-pad			\

test/degenerate-pen.c

@@ -0,0 +1,104 @@
+/*
+ * 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 D. Worth <cworth@cworth.org>
+ */
+
+#include "cairo-test.h"
+
+static cairo_test_draw_function_t draw;
+
+#define SIZE   20
+#define PAD    5
+#define WIDTH  (PAD + 3 * (PAD + SIZE) + PAD)
+#define HEIGHT (PAD + SIZE + PAD)
+
+/* We're demonstrating here a bug originally reported by Benjamin Otte
+ * on the cairo mailing list here, (after he ran into this problem
+ * with various flash animations):
+ *
+ *	[cairo] Assertion `i < pen->num_vertices' failed in 1.4.10
+ *	http://lists.cairographics.org/archives/cairo/2007-August/011282.html
+ *
+ * The problem shows up with an extreme transformation matrix that
+ * collapses the pen to a single line, (which means that
+ * _cairo_slope_compare cannot handle adjacent vertices in the pen
+ * since they have parallel slope).
+ *
+ * This test case tests degenerate pens in several directions and uses
+ * round caps to force the stroking code to attempt to walk around the
+ * pen doing slope comparisons.
+ */
+
+cairo_test_t test = {
+    "degenerate-pen",
+    "Test round joins with a pen that's transformed to a line",
+    WIDTH, HEIGHT,
+    draw
+};
+
+static cairo_test_status_t
+draw (cairo_t *cr, int width, int height)
+{
+    cairo_set_line_join (cr, CAIRO_LINE_JOIN_ROUND);
+
+    cairo_translate (cr, PAD, PAD);
+
+    /* First compress the pen to a vertical line. */
+    cairo_rectangle (cr, 0, 0, SIZE, SIZE);
+    cairo_save (cr);
+    {
+	cairo_scale (cr, 0.000001, 1.0);
+	cairo_stroke (cr);
+    }
+    cairo_restore (cr);
+
+    cairo_translate (cr, PAD + SIZE, 0);
+
+    /* Then compress the pen to a horizontal line. */
+    cairo_rectangle (cr, 0, 0, SIZE, SIZE);
+    cairo_save (cr);
+    {
+	cairo_scale (cr, 1.0, 0.000001);
+	cairo_stroke (cr);
+    }
+    cairo_restore (cr);
+
+    cairo_translate (cr, PAD + SIZE, 0);
+
+    /* Finally a line at an angle. */
+    cairo_rectangle (cr, 0, 0, SIZE, SIZE);
+    cairo_save (cr);
+    {
+	cairo_rotate (cr, M_PI / 4.0);
+	cairo_scale (cr, 0.000001, 1.0);
+	cairo_stroke (cr);
+    }
+    cairo_restore (cr);
+}
+
+int
+main (void)
+{
+    return cairo_test (&test);
+}