pixman-filter: integral splitting is only needed for triangle filter

Only the triangle is discontinuous at 0. The other filters resemble a
cubic closely enough that Simpsons integration works without
splitting.

Changes by Søren: Rebase without the changes to the integral function,
update comment to match the new code.

Signed-off-by: Bill Spitzak <spitzak@gmail.com>
Signed-off-by: Søren Sandmann <soren.sandmann@gmail.com>
Reviewed-by: Søren Sandmann <soren.sandmann@gmail.com>

diff --git a/pixman/pixman-filter.c b/pixman/pixman-filter.c
index ecff852b5c5ff073f4a230f75205f10ba6c77f36..878cf9d491a49ab5805f2acf06250e7227e5191b 100644 (file)
--- a/pixman/pixman-filter.c
+++ b/pixman/pixman-filter.c
@@ -160,18 +160,17 @@ integral (pixman_kernel_t kernel1, double x1,
          pixman_kernel_t kernel2, double scale, double x2,
          double width)
 {
-    /* If the integration interval crosses zero, break it into
-     * two separate integrals. This ensures that filters such
-     * as LINEAR that are not differentiable at 0 will still
-     * integrate properly.
+    /* The LINEAR filter is not differentiable at 0, so if the
+     * integration interval crosses zero, break it into two
+     * separate integrals.
      */
-    if (x1 < 0 && x1 + width > 0)
+    if (kernel1 == PIXMAN_KERNEL_LINEAR && x1 < 0 && x1 + width > 0)
     {
        return
            integral (kernel1, x1, kernel2, scale, x2, - x1) +
            integral (kernel1, 0, kernel2, scale, x2 - x1, width + x1);
     }
-    else if (x2 < 0 && x2 + width > 0)
+    else if (kernel2 == PIXMAN_KERNEL_LINEAR && x2 < 0 && x2 + width > 0)
     {
        return
            integral (kernel1, x1, kernel2, scale, x2, - x2) +