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image: Use consistent rounding modes for a1 rasterisation.

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When checking if the traps are equivalent to a set of rectangles, we
need to use the same rounding mode as when converting the traps to a set
of boxes and then filling them. Failure to do leads to a situation where
(-127,-128) was thought to be equivalent to (0,0) but we attempted to
fill from 0 to -1 instead.

References:
  http://lists.cairographics.org/archives/cairo/2010-June/020115.html
This commit is contained in:
Chris Wilson 2010-06-17 08:50:31 +01:00
parent 3306bcb1d9
commit 36b4b0631c
1 changed files with 33 additions and 21 deletions
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54
src/cairo-image-surface.c
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@ -2889,7 +2889,6 @@ _composite_boxes (cairo_image_surface_t *dst,
cairo_box_t *box = chunk->base;
for (i = 0; i < chunk->count; i++) {
/* round down here to match Pixman's behavior when using traps. */
int x1 = _cairo_fixed_integer_round_down (box[i].p1.x);
int y1 = _cairo_fixed_integer_round_down (box[i].p1.y);
int x2 = _cairo_fixed_integer_round_down (box[i].p2.x);
@ -2945,10 +2944,10 @@ _composite_boxes (cairo_image_surface_t *dst,
const cairo_box_t *box = chunk->base;
for (i = 0; i < chunk->count; i++) {
int x1 = _cairo_fixed_integer_round (box[i].p1.x);
int y1 = _cairo_fixed_integer_round (box[i].p1.y);
int x2 = _cairo_fixed_integer_round (box[i].p2.x);
int y2 = _cairo_fixed_integer_round (box[i].p2.y);
int x1 = _cairo_fixed_integer_round_down (box[i].p1.x);
int y1 = _cairo_fixed_integer_round_down (box[i].p1.y);
int x2 = _cairo_fixed_integer_round_down (box[i].p2.x);
int y2 = _cairo_fixed_integer_round_down (box[i].p2.y);
if (x2 == x1 || y2 == y1)
continue;
@ -3015,7 +3014,7 @@ _clip_and_composite_boxes (cairo_image_surface_t *dst,
static cairo_bool_t
_mono_edge_is_vertical (const cairo_line_t *line)
{
return _cairo_fixed_integer_round (line->p1.x) == _cairo_fixed_integer_round (line->p2.x);
return _cairo_fixed_integer_round_down (line->p1.x) == _cairo_fixed_integer_round_down (line->p2.x);
}
static cairo_bool_t
@ -3053,7 +3052,8 @@ _traps_are_pixel_aligned (cairo_traps_t *traps,
static void
_boxes_for_traps (cairo_boxes_t *boxes,
cairo_traps_t *traps)
cairo_traps_t *traps,
cairo_antialias_t antialias)
{
int i;
@ -3064,21 +3064,33 @@ _boxes_for_traps (cairo_boxes_t *boxes,
boxes->chunks.count = traps->num_traps;
boxes->chunks.size = traps->num_traps;
for (i = 0; i < traps->num_traps; i++) {
cairo_fixed_t x1 = traps->traps[i].left.p1.x;
cairo_fixed_t x2 = traps->traps[i].right.p1.x;
cairo_fixed_t y1 = traps->traps[i].top;
cairo_fixed_t y2 = traps->traps[i].bottom;
if (antialias != CAIRO_ANTIALIAS_NONE) {
for (i = 0; i < traps->num_traps; i++) {
cairo_fixed_t x1 = traps->traps[i].left.p1.x;
cairo_fixed_t x2 = traps->traps[i].right.p1.x;
cairo_fixed_t y1 = traps->traps[i].top;
cairo_fixed_t y2 = traps->traps[i].bottom;
boxes->chunks.base[i].p1.x = x1;
boxes->chunks.base[i].p1.y = y1;
boxes->chunks.base[i].p2.x = x2;
boxes->chunks.base[i].p2.y = y2;
boxes->chunks.base[i].p1.x = x1;
boxes->chunks.base[i].p1.y = y1;
boxes->chunks.base[i].p2.x = x2;
boxes->chunks.base[i].p2.y = y2;
if (boxes->is_pixel_aligned) {
boxes->is_pixel_aligned =
_cairo_fixed_is_integer (x1) && _cairo_fixed_is_integer (y1) &&
_cairo_fixed_is_integer (x2) && _cairo_fixed_is_integer (y2);
if (boxes->is_pixel_aligned) {
boxes->is_pixel_aligned =
_cairo_fixed_is_integer (x1) && _cairo_fixed_is_integer (y1) &&
_cairo_fixed_is_integer (x2) && _cairo_fixed_is_integer (y2);
}
}
} else {
boxes->is_pixel_aligned = TRUE;
for (i = 0; i < traps->num_traps; i++) {
/* round down here to match Pixman's behavior when using traps. */
boxes->chunks.base[i].p1.x = _cairo_fixed_round_down (traps->traps[i].left.p1.x);
boxes->chunks.base[i].p1.y = _cairo_fixed_round_down (traps->traps[i].top);
boxes->chunks.base[i].p2.x = _cairo_fixed_round_down (traps->traps[i].right.p1.x);
boxes->chunks.base[i].p2.y = _cairo_fixed_round_down (traps->traps[i].bottom);
}
}
}
@ -3127,7 +3139,7 @@ _clip_and_composite_trapezoids (cairo_image_surface_t *dst,
{
cairo_boxes_t boxes;
_boxes_for_traps (&boxes, traps);
_boxes_for_traps (&boxes, traps, antialias);
return _clip_and_composite_boxes (dst, op, src,
&boxes, antialias,
extents, clip);