test: Add an aliasing test case.

Just a simple test in drawing neighbouring edges and looking for the
effects of aliasing.

test/Makefile.am

@@ -140,6 +140,9 @@ REFERENCE_IMAGES = \
 	a1-traps-sample.ref.png \
 	a1-traps-sample.quartz.xfail.png \
 	a8-mask.ref.png \
+	aliasing.ref.png \
+	aliasing.image16.ref.png \
+	aliasing.xlib.ref.png \
 	alpha-similar.gl.argb32.xfail.png \
 	alpha-similar.gl.rgb24.xfail.png \
 	alpha-similar.pdf.argb32.xfail.png \

test/Makefile.sources

@@ -4,6 +4,7 @@ test_sources = \
 	a1-mask-sample.c 				\
 	a1-traps-sample.c				\
 	a8-mask.c					\
+	aliasing.c					\
 	alpha-similar.c					\
 	big-line.c					\
 	big-trap.c					\

test/aliasing.c

@@ -0,0 +1,98 @@
+/*
+ * Copyright 2010 Intel Corporation
+ *
+ * Permission is hereby granted, free of charge, to any person
+ * obtaining a copy of this software and associated documentation
+ * files (the "Software"), to deal in the Software without
+ * restriction, including without limitation the rights to use, copy,
+ * modify, merge, publish, distribute, sublicense, and/or sell copies
+ * of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+ * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+ * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ *
+ * Author: Chris Wilson <chris@chris-wilson.co.uk>
+ */
+
+#include "cairo-test.h"
+
+/* A fun little test to explore color fringing in various experimental
+ * subpixel rasterisation techniques.
+ */
+
+#define WIDTH 60
+#define HEIGHT 40
+
+static const  struct color {
+    double red, green, blue;
+} color[] = {
+    { 1, 1, 1 },
+    { 0, 0, 0 },
+    { 1, 0, 0 },
+    { 0, 1, 0 },
+    { 0, 0, 1 }
+};
+#define NUM_COLORS (sizeof (color) / sizeof (color[0]))
+#ifndef MAX
+#define MAX(a, b) ((a) > (b) ? (a) : (b))
+#endif
+
+static void
+object (cairo_t *cr, const struct color *fg, const struct color *bg)
+{
+    cairo_set_source_rgb (cr, bg->red, bg->green, bg->blue);
+    cairo_rectangle (cr, 0, 0, WIDTH, HEIGHT);
+    cairo_fill (cr);
+
+    cairo_set_source_rgb (cr, fg->red, fg->green, fg->blue);
+    cairo_save (cr);
+    cairo_scale (cr, WIDTH, HEIGHT);
+    cairo_arc (cr, .5, .5, .5 - 4. / MAX (WIDTH, HEIGHT), 0, 2 * M_PI);
+    cairo_fill (cr);
+    cairo_arc (cr, .5, .5, .5 - 2. / MAX (WIDTH, HEIGHT), 0, 2 * M_PI);
+    cairo_restore (cr);
+    cairo_set_line_width (cr, 1.);
+    cairo_stroke (cr);
+
+    cairo_set_source_rgb (cr, bg->red, bg->green, bg->blue);
+    cairo_set_line_width (cr, 4.);
+    cairo_move_to (cr, 4, HEIGHT-4);
+    cairo_line_to (cr, WIDTH-12, 4);
+    cairo_move_to (cr, 12, HEIGHT-4);
+    cairo_line_to (cr, WIDTH-4, 4);
+    cairo_stroke (cr);
+}
+
+static cairo_test_status_t
+draw (cairo_t *cr, int width, int height)
+{
+    unsigned int i, j;
+
+    for (i = 0; i < NUM_COLORS; i++) {
+	for (j = 0; j < NUM_COLORS; j++) {
+	    cairo_save (cr);
+	    cairo_translate (cr, i * WIDTH, j * HEIGHT);
+	    object (cr, &color[i], &color[j]);
+	    cairo_restore (cr);
+	}
+    }
+
+    return CAIRO_TEST_SUCCESS;
+}
+
+CAIRO_TEST (aliasing,
+	    "Check for subpixel aliasing and color fringing",
+	    "rasterisation", /* keywords */
+	    "target=raster", /* requirements */
+	    NUM_COLORS * WIDTH, NUM_COLORS * HEIGHT,
+	    NULL, draw)