Add a test for radial gradients

radial-test is a port of the radial-gradient test from the cairo test
suite. It has been modified so that some pixels have 0 in both the a
and b coefficients of the quadratic equation solved by the rasterizer,
to expose a division by zero in the original implementation.

2 files changed, 202 insertions, 0 deletions

diff --git a/test/Makefile.am b/test/Makefile.am
index 71e5353..8d8471d 100644
--- a/test/Makefile.am
+++ b/test/Makefile.am
@@ -92,6 +92,7 @@ TESTPROGRAMS_GTK =		\
 	clip-in			\
 	composite-test		\
 	gradient-test		\
+	radial-test		\
 	alpha-test		\
 	screen-test		\
 	convolution-test	\
@@ -102,6 +103,9 @@ INCLUDES += $(GTK_CFLAGS)
 gradient_test_LDADD = $(GTK_LDADD)
 gradient_test_SOURCES = gradient-test.c $(GTK_UTILS)
 
+radial_test_LDADD = $(GTK_LDADD)
+radial_test_SOURCES = radial-test.c utils.c utils.h $(GTK_UTILS)
+
 alpha_test_LDADD = $(GTK_LDADD)
 alpha_test_SOURCES = alpha-test.c $(GTK_UTILS)
 
diff --git a/test/radial-test.c b/test/radial-test.c
new file mode 100644
index 0000000..5d716c3
--- /dev/null
+++ b/test/radial-test.c
@@ -0,0 +1,198 @@
+#include "utils.h"
+#include "gtk-utils.h"
+
+#define NUM_GRADIENTS 7
+#define NUM_STOPS 3
+#define NUM_REPEAT 4
+#define SIZE 128
+#define WIDTH (SIZE * NUM_GRADIENTS)
+#define HEIGHT (SIZE * NUM_REPEAT)
+
+/*
+ * We want to test all the possible relative positions of the start
+ * and end circle:
+ *
+ *  - The start circle can be smaller/equal/bigger than the end
+ *    circle. A radial gradient can be classified in one of these
+ *    three cases depending on the sign of dr.
+ *
+ *  - The smaller circle can be completely inside/internally
+ *    tangent/outside (at least in part) of the bigger circle. This
+ *    classification is the same as the one which can be computed by
+ *    examining the sign of a = (dx^2 + dy^2 - dr^2).
+ *
+ *  - If the two circles have the same size, neither can be inside or
+ *    internally tangent
+ *
+ * This test draws radial gradients whose circles always have the same
+ * centers (0, 0) and (1, 0), but with different radiuses. From left
+ * to right:
+ *
+ * - Small start circle completely inside the end circle
+ *     0.25 -> 1.75; dr =  1.5 > 0; a = 1 - 1.50^2 < 0
+ *
+ * - Small start circle internally tangent to the end circle
+ *     0.50 -> 1.50; dr =  1.0 > 0; a = 1 - 1.00^2 = 0
+ *
+ * - Small start circle outside of the end circle
+ *     0.50 -> 1.00; dr =  0.5 > 0; a = 1 - 0.50^2 > 0
+ *
+ * - Start circle with the same size as the end circle
+ *     1.00 -> 1.00; dr =  0.0 = 0; a = 1 - 0.00^2 > 0
+ *
+ * - Small end circle outside of the start circle
+ *     1.00 -> 0.50; dr = -0.5 > 0; a = 1 - 0.50^2 > 0
+ *
+ * - Small end circle internally tangent to the start circle
+ *     1.50 -> 0.50; dr = -1.0 > 0; a = 1 - 1.00^2 = 0
+ *
+ * - Small end circle completely inside the start circle
+ *     1.75 -> 0.25; dr = -1.5 > 0; a = 1 - 1.50^2 < 0
+ *
+ */
+
+const static double radiuses[NUM_GRADIENTS] = {
+    0.25,
+    0.50,
+    0.50,
+    1.00,
+    1.00,
+    1.50,
+    1.75
+};
+
+#define double_to_color(x)					\
+    (((uint32_t) ((x)*65536)) - (((uint32_t) ((x)*65536)) >> 16))
+
+#define PIXMAN_STOP(offset,r,g,b,a)		\
+    { pixman_double_to_fixed (offset),		\
+	{					\
+	double_to_color (r),			\
+	double_to_color (g),			\
+	double_to_color (b),			\
+	double_to_color (a)			\
+	}					\
+    }
+
+static const pixman_gradient_stop_t stops[NUM_STOPS] = {
+    PIXMAN_STOP (0.0,        1, 0, 0, 0.75),
+    PIXMAN_STOP (0.70710678, 0, 1, 0, 0),
+    PIXMAN_STOP (1.0,        0, 0, 1, 1)
+};
+
+static pixman_image_t *
+create_radial (int index)
+{
+    pixman_point_fixed_t p0, p1;
+    pixman_fixed_t r0, r1;
+    double x0, x1, radius0, radius1, left, right, center;
+
+    x0 = 0;
+    x1 = 1;
+    radius0 = radiuses[index];
+    radius1 = radiuses[NUM_GRADIENTS - index - 1];
+
+    /* center the gradient */
+    left = MIN (x0 - radius0, x1 - radius1);
+    right = MAX (x0 + radius0, x1 + radius1);
+    center = (left + right) * 0.5;
+    x0 -= center;
+    x1 -= center;
+
+    /* scale to make it fit within a 1x1 rect centered in (0,0) */
+    x0 *= 0.25;
+    x1 *= 0.25;
+    radius0 *= 0.25;
+    radius1 *= 0.25;
+
+    p0.x = pixman_double_to_fixed (x0);
+    p0.y = pixman_double_to_fixed (0);
+
+    p1.x = pixman_double_to_fixed (x1);
+    p1.y = pixman_double_to_fixed (0);
+
+    r0 = pixman_double_to_fixed (radius0);
+    r1 = pixman_double_to_fixed (radius1);
+
+    return pixman_image_create_radial_gradient (&p0, &p1,
+						r0, r1,
+						stops, NUM_STOPS);
+}
+
+static const pixman_repeat_t repeat[NUM_REPEAT] = {
+    PIXMAN_REPEAT_NONE,
+    PIXMAN_REPEAT_NORMAL,
+    PIXMAN_REPEAT_REFLECT,
+    PIXMAN_REPEAT_PAD
+};
+
+int
+main (int argc, char **argv)
+{
+    pixman_transform_t transform;
+    pixman_image_t *src_img, *dest_img;
+    int i, j;
+
+    enable_fp_exceptions ();
+
+    dest_img = pixman_image_create_bits (PIXMAN_a8r8g8b8,
+					 WIDTH, HEIGHT,
+					 NULL, 0);
+
+    pixman_transform_init_identity (&transform);
+
+    /*
+     * The create_radial() function returns gradients centered in the
+     * origin and whose interesting part fits a 1x1 square. We want to
+     * paint these gradients on a SIZExSIZE square and to make things
+     * easier we want the origin in the top-left corner of the square
+     * we want to see.
+     */
+    pixman_transform_translate (NULL, &transform,
+				pixman_double_to_fixed (0.5),
+				pixman_double_to_fixed (0.5));
+
+    pixman_transform_scale (NULL, &transform,
+			    pixman_double_to_fixed (SIZE),
+			    pixman_double_to_fixed (SIZE));
+
+    /*
+     * Gradients are evaluated at the center of each pixel, so we need
+     * to translate by half a pixel to trigger some interesting
+     * cornercases. In particular, the original implementation of PDF
+     * radial gradients tried to divide by 0 when using this transform
+     * on the "tangent circles" cases.
+     */
+    pixman_transform_translate (NULL, &transform,
+				pixman_double_to_fixed (0.5),
+				pixman_double_to_fixed (0.5));
+
+    for (i = 0; i < NUM_GRADIENTS; i++)
+    {
+	src_img = create_radial (i);
+	pixman_image_set_transform (src_img, &transform);
+
+	for (j = 0; j < NUM_REPEAT; j++)
+	{
+	    pixman_image_set_repeat (src_img, repeat[j]);
+
+	    pixman_image_composite32 (PIXMAN_OP_OVER,
+				      src_img,
+				      NULL,
+				      dest_img,
+				      0, 0,
+				      0, 0,
+				      i * SIZE, j * SIZE,
+				      SIZE, SIZE);
+
+	}
+
+	pixman_image_unref (src_img);
+    }
+
+    show_image (dest_img);
+
+    pixman_image_unref (dest_img);
+
+    return 0;
+}