test: Add a simple exercise for raster sampling of subpixel geometry

Test that the rasteriser doesn't incorrectly merge disjoint geometry at
the subpixel level.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

test/Makefile.sources

@@ -280,6 +280,7 @@ test_sources = \
 	rotated-clip.c					\
 	rounded-rectangle-fill.c			\
 	rounded-rectangle-stroke.c			\
+	sample.c					\
 	scale-down-source-surface-paint.c		\
 	scale-offset-image.c				\
 	scale-offset-similar.c				\

test/sample.c

@@ -0,0 +1,117 @@
+/*
+ * Copyright 2012 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"
+
+/* Test the fidelity of the rasterisation, because Cairo is my favourite
+ * driver test suite.
+ */
+
+#define GENERATE_REFERENCE 0
+
+#define WIDTH 256
+#define HEIGHT 40
+
+#include "../src/cairo-fixed-type-private.h"
+#define PRECISION (1 << CAIRO_FIXED_FRAC_BITS)
+
+static cairo_test_status_t
+vertical (cairo_t *cr, int width, int height)
+{
+    int x;
+
+    cairo_set_source_rgb (cr, 0.0, 0.0, 0.0);
+    cairo_paint (cr);
+
+    cairo_set_source_rgba (cr, 1, 1, 1, 1);
+    for (x = -HEIGHT*PRECISION-2; x <= (WIDTH+HEIGHT)*PRECISION+2; x += 4) {
+	cairo_move_to (cr, x / (double)PRECISION - 2, -2);
+	cairo_rel_line_to (cr, 0, HEIGHT + 4);
+    }
+    cairo_set_line_width (cr, 2 / (double)PRECISION);
+    cairo_stroke (cr);
+
+    return CAIRO_TEST_SUCCESS;
+}
+
+static cairo_test_status_t
+horizontal (cairo_t *cr, int width, int height)
+{
+    int x;
+
+    cairo_set_source_rgb (cr, 0.0, 0.0, 0.0);
+    cairo_paint (cr);
+
+    cairo_set_source_rgba (cr, 1, 1, 1, 1);
+    for (x = -HEIGHT*PRECISION-2; x <= (WIDTH+HEIGHT)*PRECISION+2; x += 4) {
+	cairo_move_to (cr, -2, x / (double)PRECISION - 2);
+	cairo_rel_line_to (cr, HEIGHT + 4, 0);
+    }
+    cairo_set_line_width (cr, 2 / (double)PRECISION);
+    cairo_stroke (cr);
+
+    return CAIRO_TEST_SUCCESS;
+}
+
+static cairo_test_status_t
+diagonal (cairo_t *cr, int width, int height)
+{
+    int x;
+
+    cairo_set_source_rgb (cr, 0.0, 0.0, 0.0);
+    cairo_paint (cr);
+
+    cairo_set_source_rgba (cr, 1, 1, 1, 1);
+    for (x = -HEIGHT*PRECISION-2; x <= (WIDTH+HEIGHT)*PRECISION+2; x += 6) {
+	cairo_move_to (cr, x / (double)PRECISION - 2, -2);
+	cairo_rel_line_to (cr, HEIGHT + 4, HEIGHT + 4);
+    }
+    cairo_set_line_width (cr, 2 / (double)PRECISION);
+    cairo_stroke (cr);
+
+    return CAIRO_TEST_SUCCESS;
+}
+
+CAIRO_TEST (sample_vertical,
+	    "Check the fidelity of the rasterisation.",
+	    NULL, /* keywords */
+	    "target=raster slow", /* requirements */
+	    WIDTH, HEIGHT,
+	    NULL, vertical)
+
+CAIRO_TEST (sample_horizontal,
+	    "Check the fidelity of the rasterisation.",
+	    NULL, /* keywords */
+	    "target=raster slow", /* requirements */
+	    WIDTH, HEIGHT,
+	    NULL, vertical)
+
+CAIRO_TEST (sample_diagonal,
+	    "Check the fidelity of the rasterisation.",
+	    NULL, /* keywords */
+	    "target=raster slow", /* requirements */
+	    WIDTH, HEIGHT,
+	    NULL, diagonal)