Improve handling of tangent circles

When b is 0, avoid the division by zero and just return transparent
black.

When the solution t would have an invalid radius (negative or outside
[0,1] for none-extended gradients), return transparent black.

1 files changed, 18 insertions, 2 deletions

diff --git a/pixman/pixman-radial-gradient.c b/pixman/pixman-radial-gradient.c
index b595ba7..7b92307 100644
--- a/pixman/pixman-radial-gradient.c
+++ b/pixman/pixman-radial-gradient.c
@@ -96,8 +96,24 @@ radial_compute_color (double                    a,
 
     if (a == 0)
     {
-	return _pixman_gradient_walker_pixel (walker,
-					      pixman_fixed_1 / 2 * c / b);
+	double t;
+
+	if (b == 0)
+	    return 0;
+
+	t = pixman_fixed_1 / 2 * c / b;
+	if (repeat == PIXMAN_REPEAT_NONE)
+	{
+	    if (0 <= t && t <= pixman_fixed_1)
+		return _pixman_gradient_walker_pixel (walker, t);
+	}
+	else
+	{
+	    if (t * dr > mindr)
+		return _pixman_gradient_walker_pixel (walker, t);
+	}
+
+	return 0;
     }
 
     det = fdot (b, a, 0, b, -c, 0);