test: Add cases to exercise clipping after no-ops

Whilst investigating:

  Bug 31788: SVG <line> with y1 == y2 and both with fractional
             part don't render
  https://bugs.webkit.org/show_bug.cgi?id=31788

I found that it can be reduced to a no-op clip following a no-op stroke
or fill. These conditions are exercised here and are shown to be a bug
introduced in the 1.9.x development series.

1 files changed, 66 insertions, 0 deletions

diff --git a/test/clip-stroke-no-op.c b/test/clip-stroke-no-op.c
new file mode 100644
index 000000000..e727fc468
--- /dev/null
+++ b/test/clip-stroke-no-op.c
@@ -0,0 +1,66 @@
+/*
+ * Copyright 2009 Benjamin Otte
+ *
+ * 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
+ * Benjamin Otte not be used in advertising or publicity pertaining to
+ * distribution of the software without specific, written prior
+ * permission. Benjamin Otte makes no representations about the
+ * suitability of this software for any purpose.  It is provided "as
+ * is" without express or implied warranty.
+ *
+ * BENJAMIN OTTE DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS
+ * SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS, IN NO EVENT SHALL BENJAMIN OTTE 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: Benjamin Otte <otte@gnome.org>
+ */
+
+#include "cairo-test.h"
+
+#define WIDTH 50
+#define HEIGHT 50
+
+static cairo_test_status_t
+draw (cairo_t *cr, int width, int height)
+{
+    /* Neutral gray background */
+    cairo_set_source_rgb (cr, 0.5, 0.5, 0.5);
+    cairo_paint (cr);
+
+    /* remove this clip operation and everything works */
+    cairo_rectangle (cr, 10, 10, 30, 30);
+    cairo_clip (cr);
+
+    /* remove this no-op and everything works */
+    cairo_stroke (cr);
+
+    /* make the y coordinates integers and everything works */
+    cairo_move_to (cr, 20, 20.101562);
+    cairo_line_to (cr, 30, 20.101562);
+
+    /* This clip operation should fail to work. But with cairo 1.9, if all the 
+     * 3 cases above happen, the clip will not work and the paint will happen.
+     */
+    cairo_save (cr); {
+	cairo_set_source_rgba (cr, 1, 0.5, 0.5, 1);
+	cairo_clip_preserve (cr);
+	cairo_paint (cr);
+    } cairo_restore (cr);
+
+    return CAIRO_TEST_SUCCESS;
+}
+
+CAIRO_TEST (clip_stroke_no_op,
+	    "Exercises a bug found by Benjamin Otte whereby a no-op clip is nullified by a stroke",
+	    "clip, stroke", /* keywords */
+	    NULL, /* requirements */
+	    WIDTH, HEIGHT,
+	    NULL, draw)