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Replace an outdated (after f0e2cd44) comment with clarification in _cairo_gstate_copy_transformed_pattern

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This commit is contained in:
Anton Danilkin 2021-04-24 14:55:19 +02:00
parent de2a71b230
commit 8d02744136
1 changed files with 14 additions and 1 deletions
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15
src/cairo-gstate.c
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@ -937,9 +937,22 @@ _cairo_gstate_copy_transformed_pattern (cairo_gstate_t *gstate,
const cairo_pattern_t *original,
const cairo_matrix_t *ctm_inverse)
{
/*
* What calculations below do can be described in pseudo-code (so using nonexistent fields) as (using column vectors):
* pattern->matrix = surface->device_transform *
* pattern->matrix *
* ctm_inverse *
* gstate->target->device_transform_inverse
*
* The inverse of which is:
* pattern->matrix_inverse = gstate->target->device_transform *
* ctm *
* pattern->matrix_inverse *
* surface->device_transform_inverse
*/
_cairo_gstate_copy_pattern (pattern, original);
/* apply device_transform first so that it is transformed by ctm_inverse */
if (original->type == CAIRO_PATTERN_TYPE_SURFACE) {
cairo_surface_pattern_t *surface_pattern;
cairo_surface_t *surface;