[test] Exercise degenerate dashes.

Add a test case to capture the current behaviour when a segment ends on
an off/on dash transition.

Originally filed as bug:
  Miter artifacts for dashed strokes
  https://bugs.freedesktop.org/show_bug.cgi?id=17973

test/.gitignore

@@ -52,6 +52,7 @@ dash-scale
 dash-state
 dash-zero-length
 degenerate-arc
+degenerate-dash
 degenerate-path
 degenerate-pen
 device-offset

test/Makefile.am

@@ -42,6 +42,7 @@ dash-scale$(EXEEXT)					\
 dash-state$(EXEEXT)					\
 dash-zero-length$(EXEEXT)				\
 degenerate-arc$(EXEEXT)					\
+degenerate-dash$(EXEEXT)				\
 degenerate-path$(EXEEXT)				\
 degenerate-pen$(EXEEXT)					\
 device-offset$(EXEEXT)					\
@@ -395,6 +396,7 @@ REFERENCE_IMAGES = \
 	degenerate-arc-ref.png		\
 	degenerate-arc-ps2-ref.png	\
 	degenerate-arc-ps3-ref.png	\
+	degenerate-dash-ref.png		\
 	degenerate-pen-ref.png		\
 	degenerate-pen-ps2-ref.png	\
 	degenerate-pen-ps3-ref.png	\

test/degenerate-dash.c

@@ -0,0 +1,97 @@
+/*
+ * Copyright © 2008 Chris Wilson
+ *
+ * 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
+ * Chris Wilson not be used in advertising or publicity pertaining to
+ * distribution of the software without specific, written prior
+ * permission. Chris Wilson makes no representations about the
+ * suitability of this software for any purpose.  It is provided "as
+ * is" without express or implied warranty.
+ *
+ * CHRIS WILSON DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS
+ * SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS, IN NO EVENT SHALL CHRIS WILSON 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: Chris Wilson <chris@chris-wilson.co.uk>
+ *
+ * Based on an original test case by M Joonas Pihlaja.
+ */
+
+#include "cairo-test.h"
+
+#ifndef ARRAY_LENGTH
+#define ARRAY_LENGTH(A) (int) (sizeof (A) / sizeof ((A)[0]))
+#endif
+
+#define PAD 5
+
+static cairo_test_draw_function_t draw;
+
+static const cairo_test_t test = {
+    "degenerate-dash",
+    "Tests the behaviour of dashed segments that end on a off-on transition",
+    210 + 2*PAD, 210 + 2*PAD,
+    draw
+};
+
+static cairo_test_status_t
+draw (cairo_t *cr, int width, int height)
+{
+    const double dashes[] = { 25, 25 };
+    cairo_line_join_t joins[] = {
+	CAIRO_LINE_JOIN_ROUND,
+	CAIRO_LINE_JOIN_MITER,
+	CAIRO_LINE_JOIN_BEVEL
+    };
+    cairo_line_cap_t caps[] = {
+	CAIRO_LINE_CAP_ROUND,
+	CAIRO_LINE_CAP_SQUARE,
+	CAIRO_LINE_CAP_BUTT,
+    };
+    int i, j;
+
+    cairo_set_source_rgb (cr, 1,1,1);
+    cairo_paint (cr);
+
+    cairo_set_source_rgb (cr, 1, 0, 0);
+
+    cairo_set_dash (cr, dashes, 2, 0.);
+    cairo_set_line_width (cr, 10);
+
+    cairo_translate (cr, 5 + PAD, 5 + PAD);
+
+    for (i = 0; i < ARRAY_LENGTH (joins); i++) {
+	cairo_set_line_join (cr, joins[i]);
+	cairo_save (cr);
+
+	for (j = 0; j < ARRAY_LENGTH (caps); j++) {
+	    cairo_set_line_cap (cr, caps[j]);
+
+	    cairo_move_to (cr,  0, 0);
+	    cairo_line_to (cr, 50, 0);
+	    cairo_line_to (cr, 50,50);
+	    cairo_stroke (cr);
+
+	    cairo_translate (cr, 75, 0);
+	}
+	cairo_restore (cr);
+
+	cairo_translate (cr, 0, 75);
+    }
+
+    return CAIRO_TEST_SUCCESS;
+}
+
+int
+main (void)
+{
+    return cairo_test (&test);
+}