[Pixman] [PATCH 3/3] BILINEAR->NEAREST filter optimization for simple rotation and translation

[Siarhei Siamashka]

From: Siarhei Siamashka <siarhei.siamashka at nokia.com>

Simple rotation and translation are the additional cases when BILINEAR
filter can be safely reduced to NEAREST.
---
 pixman/pixman-image.c |   37 +++++++++++++++++++++++++++++++++++++
 1 files changed, 37 insertions(+), 0 deletions(-)

diff --git a/pixman/pixman-image.c b/pixman/pixman-image.c
index 4784c22..583e7a7 100644
--- a/pixman/pixman-image.c
+++ b/pixman/pixman-image.c
@@ -256,6 +256,43 @@ 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)
+	         )
+	        )
+	{
+	    /* 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_BILINEAR_FILTER;
+	    }
+	    else
+	    {
+		flags |= FAST_PATH_NEAREST_FILTER;
+	    }
+	}
 	else
 	{
 	    flags |= FAST_PATH_BILINEAR_FILTER;
-- 
1.7.3.4