If a transformation matrix causes a scale, a rotation not a multiple of 90
degrees or a non-integer translation then textures rendered with
it would benefit from bilinear filtering.
This test is done in a lazy fashion by examining elements of the matrix
to check for a simple pattern that indicates these conditions are met.
---
src/compositor.c | 35 +++++++++++++++++++++++++++++++++++
src/compositor.h | 4 ++++
2 files changed, 39 insertions(+)
diff --git a/src/compositor.c b/src/compositor.c
index 68fbd71..00d404d 100644
--- a/src/compositor.c
+++ b/src/compositor.c
@@ -799,6 +799,41 @@ weston_matrix_transform_region(pixman_region32_t *dest,
free(dest_rects);
}
+static bool near_zero(float a)
+{
+ if (fabs(a) > 0.0001)
+ return false;
+
+ return true;
+}
+
+WL_EXPORT bool
+weston_matrix_needs_filtering(struct weston_matrix *matrix)
+{
+ /* check for non-integral x/y translation */
+ if ((nearbyintf(matrix->d[12]) != matrix->d[12]) ||
+ (nearbyintf(matrix->d[13]) != matrix->d[13]))
+ return true;
+
+ if (!near_zero(matrix->d[3]) || !near_zero(matrix->d[7]) ||
+ !near_zero(matrix->d[15] - 1.0))
+ return true;
+
+ if (near_zero(matrix->d[0])) {
+ if (!near_zero(matrix->d[5]) ||
+ !near_zero(fabsf(matrix->d[1]) - 1.0) ||
+ !near_zero(fabsf(matrix->d[4]) - 1.0))
+ return true;
+ } else {
+ if (!near_zero(matrix->d[1]) || !near_zero(matrix->d[4]) ||
+ !near_zero(fabsf(matrix->d[0]) - 1.0) ||
+ !near_zero(fabsf(matrix->d[5]) - 1.0))
+ return true;
+ }
+
+ return false;
+}
+
WL_EXPORT void
weston_surface_to_buffer_float(struct weston_surface *surface,
float sx, float sy, float *bx, float *by)
diff --git a/src/compositor.h b/src/compositor.h
index 4fdf4dc..bc22026 100644
--- a/src/compositor.h
+++ b/src/compositor.h
@@ -28,6 +28,7 @@
extern "C" {
#endif
+#include <stdbool.h>
#include <time.h>
#include <pixman.h>
#include <xkbcommon/xkbcommon.h>
@@ -987,6 +988,9 @@ weston_view_from_global_fixed(struct weston_view *view,
wl_fixed_t x, wl_fixed_t y,
wl_fixed_t *vx, wl_fixed_t *vy);
+bool
+weston_matrix_needs_filtering(struct weston_matrix *matrix);
+
void
weston_surface_to_buffer_float(struct weston_surface *surface,
float x, float y, float *bx, float *by);
--
2.1.1
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