Eliminate self-intersecting strokes.

We refactor the surface fallbacks to convert full strokes and fills to the
intermediate polygon representation (as opposed to before where we
returned the trapezoidal representation). This allow greater flexibility
to choose how then to rasterize the polygon. Where possible we use the
local spans rasteriser for its increased performance, but still have the
option to use the tessellator instead (for example, with the current
Render protocol which does not yet have a polygon image).

In order to accommodate this, the spans interface is tweaked to accept
whole polygons instead of a path and the tessellator is tweaked for speed.

Performance Impact
==================

...
Still measuring, expecting some severe regressions.
...

1 files changed, 95 insertions, 0 deletions

diff --git a/test/clipped-trapezoids.c b/test/clipped-trapezoids.c
new file mode 100644
index 00000000..1f96daa8
--- /dev/null
+++ b/test/clipped-trapezoids.c
@@ -0,0 +1,95 @@
+/*
+ * 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>
+ */
+
+#include "cairo-test.h"
+
+static cairo_test_status_t
+draw (cairo_t *cr, int width, int height)
+{
+    double dash[2] = { 8, 4 };
+    double radius;
+
+    radius = width;
+    if (height > radius)
+	radius = height;
+
+    /* fill the background using a big circle */
+    cairo_arc (cr, 0, 0, 4 * radius, 0, 2 * M_PI);
+    cairo_fill (cr);
+
+    /* a rotated square - overlapping the corners */
+    cairo_save (cr);
+    cairo_save (cr);
+    cairo_translate (cr, width/2, height/2);
+    cairo_rotate (cr, M_PI/4);
+    cairo_scale (cr, M_SQRT2, M_SQRT2);
+    cairo_rectangle (cr, -width/2, -height/2, width, height);
+    cairo_restore (cr);
+    cairo_set_source_rgba (cr, 0, 1, 0, .5);
+    cairo_set_line_width (cr, radius/2);
+    cairo_stroke (cr);
+    cairo_restore (cr);
+
+    /* and put some circles in the corners */
+    cairo_set_source_rgb (cr, 1, 1, 1);
+    cairo_new_sub_path (cr);
+    cairo_arc (cr, 0, 0, radius/4, 0, 2 * M_PI);
+    cairo_new_sub_path (cr);
+    cairo_arc (cr, width, 0, radius/4, 0, 2 * M_PI);
+    cairo_new_sub_path (cr);
+    cairo_arc (cr, width, height, radius/4, 0, 2 * M_PI);
+    cairo_new_sub_path (cr);
+    cairo_arc (cr, 0, height, radius/4, 0, 2 * M_PI);
+    cairo_fill (cr);
+
+    /* a couple of pixel-aligned lines */
+    cairo_set_source_rgb (cr, 0, 0, 1);
+    cairo_move_to (cr, width/2, -height);
+    cairo_rel_line_to (cr, 0, 3*height);
+    cairo_move_to (cr, -width, height/2);
+    cairo_rel_line_to (cr, 3*width, 0);
+    cairo_stroke (cr);
+
+    /* a couple of dashed diagonals */
+    cairo_save (cr);
+    cairo_set_source_rgb (cr, 1, 0, 0);
+    cairo_set_dash (cr, dash, 2, 0);
+    cairo_set_line_width (cr, 4.);
+    cairo_move_to (cr, -width, -height);
+    cairo_line_to (cr, width+width, height+height);
+    cairo_move_to (cr, width+width, -height);
+    cairo_line_to (cr, -width, height+height);
+    cairo_stroke (cr);
+    cairo_restore (cr);
+
+    return CAIRO_TEST_SUCCESS;
+}
+
+CAIRO_TEST (clipped_trapezoids,
+	    "Tests clipping of trapezoids larger than the surface",
+	    "clip", /* keywords */
+	    NULL, /* requirements */
+	    40, 40,
+	    NULL, draw)