Add new test: curve-to-as-line-to

This test anticipates a future optimization, (already pushed
upstream but not pulled yet), with a buggy implementation
of replacing curve_to with line_to.

test/Makefile.sources

@@ -35,6 +35,7 @@ test_sources = \
 	create-from-png.c				\
 	create-from-png-stream.c			\
 	culled-glyphs.c					\
+	curve-to-as-line-to.c				\
 	dash-caps-joins.c				\
 	dash-curve.c					\
 	dash-no-dash.c					\

test/curve-to-as-line-to.c

@@ -0,0 +1,95 @@
+/*
+ * Copyright © 2005 Red Hat, Inc.
+ *
+ * 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>
+ */
+
+#include "cairo-test.h"
+
+#define SIZE 30
+
+/* At one point, an optimization was proposed for cairo in which a
+ * curve_to would be optimized as a line_to. The initial (buggy)
+ * implementation verified that the slopes of several segments of the
+ * spline's control polygon were identical, but left open the
+ * possibility of an anti-parallel slope for one segment.
+ *
+ * For example, given a spline with collinear control points (A,B,C,D)
+ * positioned as follows:
+ *
+ *	C--A--B--D
+ *
+ * The code verified identical slopes for AB, CD, and AD. The missing
+ * check for the BC segment allowed it to be anti-parallel to the
+ * others as above, and hence invalid to replace this spline with the
+ * AD line segment.
+ */
+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 */
+
+    cairo_translate (cr, 0, 1.0);
+
+    /* The CABD spline as described above. We ensure that the spline
+     * folds over on itself outside the bounds of the image to avoid
+     * the reference image having the curved portion of that fold,
+     * (which would just be harder to match in all the backends than
+     * we really want). */
+    cairo_move_to (cr,
+		     10.5, 0.5);
+    cairo_curve_to (cr,
+		     11.5, 0.5,
+		    -25.0, 0.5,
+		     31.0, 0.5);
+
+    cairo_stroke (cr);
+
+    cairo_translate (cr, 0, 2.0);
+
+    /* A reflected version: DBAC */
+    cairo_move_to (cr,
+		    19.5, 0.5);
+
+    cairo_curve_to (cr,
+		    18.5, 0.5,
+		    55.0, 0.5,
+		    -1.0, 0.5);
+
+    cairo_stroke (cr);
+
+    return CAIRO_TEST_SUCCESS;
+}
+
+CAIRO_TEST (curve_to_as_line_to,
+	    "Test optimization treating curve_to as line_to",
+	    "path", /* keywords */
+	    NULL, /* requirements */
+	    30,
+	    5,
+	    NULL, draw)