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[pattern] Correctly optimize away fractional translations.

Browse source 
As is so often the case, reading the commit log gives you fresh insight in
the problem - often called confessional debugging...

We can simplify the problem by ignoring attr->[xy]_offset, for the time
being, and focus on computing the correct matrix. This is comparatively
simple as all we need to do is perform the appropriate rounding on the
translation vector.
This commit is contained in:
Chris Wilson 2008-10-14 11:08:43 +01:00
parent 9886cb3353
commit 02a7ca80f9
1 changed files with 10 additions and 8 deletions
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18
src/cairo-pattern.c
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@ -1757,10 +1757,10 @@ _cairo_pattern_analyze_filter (cairo_surface_pattern_t *pattern,
}
static int
static double
_pixman_nearest_sample (double d)
{
return _cairo_lround (ceil (d - .5));
return ceil (d - .5);
}
static cairo_int_status_t
@ -1800,17 +1800,19 @@ _cairo_pattern_acquire_surface_for_surface (cairo_surface_pattern_t *pattern,
attr->matrix = pattern->base.matrix;
attr->matrix.x0 = 0;
attr->matrix.y0 = 0;
if (_cairo_matrix_is_identity (&attr->matrix)) {
if (_cairo_matrix_is_pixel_exact (&attr->matrix)) {
/* The rounding here is rather peculiar as it needs to match the
* rounding performed on the sample coordinate used by pixman.
*/
attr->x_offset = tx = _pixman_nearest_sample (pattern->base.matrix.x0);
attr->y_offset = ty = _pixman_nearest_sample (pattern->base.matrix.y0);
attr->matrix.x0 = _pixman_nearest_sample (pattern->base.matrix.x0);
attr->matrix.y0 = _pixman_nearest_sample (pattern->base.matrix.y0);
} else {
attr->matrix = pattern->base.matrix;
attr->x_offset = attr->y_offset = 0;
tx = ty = 0;
attr->matrix.x0 = pattern->base.matrix.x0;
attr->matrix.y0 = pattern->base.matrix.y0;
}
attr->x_offset = attr->y_offset = 0;
tx = ty = 0;
}
else
{