Generalize and simplify the code that reduces BILINEAR to NEAREST so
that the reduction happens for all affine transformations where
t00...t12 are integers and (t00 + t01) and (t10 + t11) are both
odd. This is a sufficient condition for the resulting transformed
coordinates to be exactly at the center of a pixel so that BILINEAR
becomes identical to NEAREST.
V2: Address some comments by Bill Spitzak
Signed-off-by: Søren Sandmann <soren.sandm...@gmail.com>
---
pixman/pixman-image.c | 66 +++++++++++++++++++++++++++++----------------------
1 file changed, 38 insertions(+), 28 deletions(-)
diff --git a/pixman/pixman-image.c b/pixman/pixman-image.c
index 1ff1a49..681864e 100644
--- a/pixman/pixman-image.c
+++ b/pixman/pixman-image.c
@@ -335,37 +335,47 @@ compute_image_info (pixman_image_t *image)
{
flags |= FAST_PATH_NEAREST_FILTER;
}
- else if (
- /* affine and integer translation components in matrix ... */
- ((flags & FAST_PATH_AFFINE_TRANSFORM) &&
- !pixman_fixed_frac (image->common.transform->matrix[0][2] |
- image->common.transform->matrix[1][2])) &&
- (
- /* ... combined with a simple rotation */
- (flags & (FAST_PATH_ROTATE_90_TRANSFORM |
- FAST_PATH_ROTATE_180_TRANSFORM |
- FAST_PATH_ROTATE_270_TRANSFORM)) ||
- /* ... or combined with a simple non-rotated translation */
- (image->common.transform->matrix[0][0] == pixman_fixed_1 &&
- image->common.transform->matrix[1][1] == pixman_fixed_1 &&
- image->common.transform->matrix[0][1] == 0 &&
- image->common.transform->matrix[1][0] == 0)
- )
- )
+ else if (flags & FAST_PATH_AFFINE_TRANSFORM)
{
- /* FIXME: there are some affine-test failures, showing that
- * handling of BILINEAR and NEAREST filter is not quite
- * equivalent when getting close to 32K for the translation
- * components of the matrix. That's likely some bug, but for
- * now just skip BILINEAR->NEAREST optimization in this case.
+ /* Suppose the transform is
+ *
+ * [ t00, t01, t02 ]
+ * [ t10, t11, t12 ]
+ * [ 0, 0, 1 ]
+ *
+ * and the destination coordinates are (n + 0.5, m + 0.5). Then
+ * the transformed x coordinate is:
+ *
+ * tx = t00 * (n + 0.5) + t01 * (m + 0.5) + t02
+ * = t00 * n + t01 * m + t02 + (t00 + t01) * 0.5
+ *
+ * which implies that if t00, t01 and t02 are all integers
+ * and (t00 + t01) is odd, then tx will be an integer plus 0.5,
+ * which means a BILINEAR filter will reduce to NEAREST. The same
+ * applies in the y direction
*/
- pixman_fixed_t magic_limit = pixman_int_to_fixed (30000);
- if (image->common.transform->matrix[0][2] <= magic_limit &&
- image->common.transform->matrix[1][2] <= magic_limit &&
- image->common.transform->matrix[0][2] >= -magic_limit &&
- image->common.transform->matrix[1][2] >= -magic_limit)
+ pixman_fixed_t (*t)[3] = image->common.transform->matrix;
+
+ if ((pixman_fixed_frac (
+ t[0][0] | t[0][1] | t[0][2] |
+ t[1][0] | t[1][1] | t[1][2]) == 0) &&
+ (pixman_fixed_to_int (
+ (t[0][0] + t[0][1]) & (t[1][0] + t[1][1])) % 2) == 1)
{
- flags |= FAST_PATH_NEAREST_FILTER;
+ /* FIXME: there are some affine-test failures, showing that
+ * handling of BILINEAR and NEAREST filter is not quite
+ * equivalent when getting close to 32K for the translation
+ * components of the matrix. That's likely some bug, but for
+ * now just skip BILINEAR->NEAREST optimization in this case.
+ */
+ pixman_fixed_t magic_limit = pixman_int_to_fixed (30000);
+ if (image->common.transform->matrix[0][2] <= magic_limit &&
+ image->common.transform->matrix[1][2] <= magic_limit &&
+ image->common.transform->matrix[0][2] >= -magic_limit &&
+ image->common.transform->matrix[1][2] >= -magic_limit)
+ {
+ flags |= FAST_PATH_NEAREST_FILTER;
+ }
}
}
break;
--
1.7.11.7
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