[test] Yet another bug in curve-to as line-to.

Andrea Canciani (ranma42) found another instance of my broken 'degenerate'
curve-to as line-to optimisation. All I can say is when I do something
wrong, at least I'm consistent!

This test case highlights the bug in the rel-curve-to path.

test/Makefile.am

@@ -306,6 +306,8 @@ REFERENCE_IMAGES = \
 	degenerate-pen.ps3.ref.png \
 	degenerate-pen.quartz.ref.png \
 	degenerate-pen.ref.png \
+	degenerate-rel-curve-to.ref.png \
+	degenerate-rel-curve-to.ps.xfail.png \
 	device-offset-fractional.gl.xfail.png \
 	device-offset-fractional.pdf.argb32.ref.png \
 	device-offset-fractional.pdf.ref.png \

test/Makefile.sources

@@ -49,6 +49,7 @@ test_sources = \
 	degenerate-dash.c				\
 	degenerate-path.c				\
 	degenerate-pen.c				\
+	degenerate-rel-curve-to.c			\
 	device-offset.c					\
 	device-offset-fractional.c			\
 	device-offset-positive.c			\

test/degenerate-rel-curve-to.c

@@ -0,0 +1,99 @@
+/*
+ * Copyright © 2005 Red Hat, Inc.
+ * Copyright © 2009 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
+ * Red Hat, Inc. not be used in advertising or publicity pertaining to
+ * distribution of the software without specific, written prior
+ * permission. Red Hat, Inc. makes no representations about the
+ * suitability of this software for any purpose.  It is provided "as
+ * is" without express or implied warranty.
+ *
+ * RED HAT, INC. DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS
+ * SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS, IN NO EVENT SHALL RED HAT, INC. 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: Carl D. Worth <cworth@cworth.org>
+ *         Chris Wilson <chris@chris-wilson.co.uk>
+ */
+
+#include "cairo-test.h"
+
+#define SIZE 30
+
+/* Another attempt at avoiding unnecessary splines was made, where
+ * a curve-to that ended on the same point as it began were discarded.
+ * The same bug was made to rel-curve-to as well, hence this test.
+ */
+static cairo_test_status_t
+draw (cairo_t *cr, int width, int height)
+{
+    cairo_set_source_rgb (cr, 1.0, 1.0, 1.0); /* white */
+    cairo_paint (cr);
+
+    cairo_set_line_width (cr, 1.0);
+    cairo_set_line_cap (cr, CAIRO_LINE_CAP_BUTT);
+    cairo_set_line_join (cr, CAIRO_LINE_JOIN_BEVEL);
+    cairo_set_source_rgb (cr, 0.0, 0.0, 0.0); /* black */
+
+    /* entirely degenerate */
+    cairo_move_to (cr, 2.5, 2.5);
+    cairo_rel_curve_to (cr,
+			0., 0.,
+			0., 0.,
+			0., 0.);
+    cairo_stroke (cr);
+
+    /* horizontal */
+    cairo_move_to (cr, 5.5, 2.5);
+    cairo_rel_curve_to (cr,
+		         10., 0.,
+			-10., 0.,
+			 0., 0.);
+    cairo_stroke (cr);
+
+    /* vertical */
+    cairo_move_to (cr, 5.5, 2.5);
+    cairo_rel_curve_to (cr,
+		        0.,  10.,
+			0., -10.,
+			0.,   0.);
+    cairo_stroke (cr);
+
+    cairo_translate (cr, 15, 0);
+
+    /* horizontal/vertical */
+    cairo_move_to (cr, 5.5, 0.5);
+    cairo_rel_curve_to (cr,
+		        -6.,  0.,
+			 0., 10.,
+			 0.,  0.);
+
+    cairo_translate (cr, 10, 0);
+
+    /* vertical/horizontal */
+    cairo_move_to (cr, 5.5, 0.0);
+    cairo_rel_curve_to (cr,
+		        0., 11.,
+			5.,  0.,
+			0.,  0.);
+    cairo_stroke (cr);
+
+    return CAIRO_TEST_SUCCESS;
+}
+
+CAIRO_TEST (degenerate_rel_curve_to,
+	    "Test optimization treating degenerate rel-curve-to as line-to",
+	    "path", /* keywords */
+	    NULL, /* requirements */
+	    40,
+	    5,
+	    NULL, draw)