fdo-mirrors/cairo
1
0
Fork 0
mirror of https://gitlab.freedesktop.org/cairo/cairo.git synced 2026-05-05 18:08:03 +02:00
Code Issues Projects Releases Packages Wiki Activity Actions

ps,pdf: Deal with empty domain gradients.

Browse source 
If all the stops of the gradient have the same offset and the
pattern's extend mode is EXTEND_PAD, then we cannot use the stops'
domain as the interpolation parameter range because this would produce
a gradient with the same start and end objects.  Such ranges tickle
bad behaviour in rasterisers.

We replace the color function with an appropriate step function
defined on [0 1].

Fixes radial-gradient-one-stop for pdf and ps3.

Reviewed-by: M Joonas Pihlaja <jpihlaja@cc.helsinki.fi>
This commit is contained in:
Andrea Canciani 2010-12-12 22:29:56 +00:00
parent 36e58aea51
commit 3cbe82fe58
2 changed files with 104 additions and 6 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

60
src/cairo-pdf-surface.c
View file

@ -2903,7 +2903,50 @@ _cairo_pdf_surface_emit_pattern_stops (cairo_pdf_surface_t *surface,
stops[n_stops-1].offset = 1.0;
}
if (n_stops <= 2) {
if (stops[0].offset == stops[n_stops - 1].offset) {
/*
* The first and the last stops have the same offset, but we
* don't want a function with an empty domain, because that
* would provoke underdefined behaviour from rasterisers.
* This can only happen with EXTEND_PAD, because EXTEND_NONE
* is optimised into a clear pattern in cairo-gstate, and
* REFLECT/REPEAT are always transformed to have the first
* stop at t=0 and the last stop at t=1. Thus we want a step
* function going from the first color to the last one.
*
* This can be accomplished by stitching three functions:
* - a constant first color function,
* - a step from the first color to the last color (with empty domain)
* - a constant last color function
*/
cairo_pdf_color_stop_t pad_stops[4];
assert (pattern->base.extend == CAIRO_EXTEND_PAD);
pad_stops[0] = pad_stops[1] = stops[0];
pad_stops[2] = pad_stops[3] = stops[n_stops - 1];
pad_stops[0].offset = 0;
pad_stops[3].offset = 1;
status = _cairo_pdf_surface_emit_stitched_colorgradient (surface,
4,
pad_stops,
FALSE,
color_function);
if (unlikely (status))
goto BAIL;
if (emit_alpha) {
status = _cairo_pdf_surface_emit_stitched_colorgradient (surface,
4,
pad_stops,
TRUE,
alpha_function);
if (unlikely (status))
goto BAIL;
}
} else if (n_stops == 2) {
/* no need for stitched function */
status = cairo_pdf_surface_emit_rgb_linear_function (surface,
&stops[0],
@ -3200,6 +3243,21 @@ _cairo_pdf_surface_emit_gradient (cairo_pdf_surface_t *surface,
bounds_x1, bounds_y1,
bounds_x2, bounds_y2,
tolerance, domain);
} else if (pattern->stops[0].offset == pattern->stops[pattern->n_stops - 1].offset) {
/*
* If the first and the last stop offset are the same, then
* the color function is a step function.
* _cairo_ps_surface_emit_pattern_stops emits it as a stitched
* function no matter how many stops the pattern has. The
* domain of the stitched function will be [0 1] in this case.
*
* This is done to avoid emitting degenerate gradients for
* EXTEND_PAD patterns having a step color function.
*/
domain[0] = 0.0;
domain[1] = 1.0;
assert (pattern->base.extend == CAIRO_EXTEND_PAD);
} else {
domain[0] = pattern->stops[0].offset;
domain[1] = pattern->stops[pattern->n_stops - 1].offset;

50
src/cairo-ps-surface.c
View file

@ -3112,7 +3112,8 @@ _cairo_ps_surface_emit_pattern_stops (cairo_ps_surface_t *surface,
}
if (pattern->base.extend == CAIRO_EXTEND_REPEAT ||
pattern->base.extend == CAIRO_EXTEND_REFLECT) {
pattern->base.extend == CAIRO_EXTEND_REFLECT)
{
if (stops[0].offset > COLOR_STOP_EPSILON) {
if (pattern->base.extend == CAIRO_EXTEND_REFLECT)
memcpy (allstops, stops, sizeof (cairo_ps_color_stop_t));
@ -3154,16 +3155,40 @@ _cairo_ps_surface_emit_pattern_stops (cairo_ps_surface_t *surface,
_cairo_output_stream_printf (surface->stream,
"/CairoFunction\n");
if (n_stops == 1) {
/* work around single stop gradients */
_cairo_ps_surface_emit_linear_colorgradient (surface, &stops[0], &stops[0]);
if (stops[0].offset == stops[n_stops - 1].offset) {
/*
* The first and the last stops have the same offset, but we
* don't want a function with an empty domain, because that
* would provoke underdefined behaviour from rasterisers.
* This can only happen with EXTEND_PAD, because EXTEND_NONE
* is optimised into a clear pattern in cairo-gstate, and
* REFLECT/REPEAT are always transformed to have the first
* stop at t=0 and the last stop at t=1. Thus we want a step
* function going from the first color to the last one.
*
* This can be accomplished by stitching three functions:
* - a constant first color function,
* - a step from the first color to the last color (with empty domain)
* - a constant last color function
*/
cairo_ps_color_stop_t pad_stops[4];
assert (pattern->base.extend == CAIRO_EXTEND_PAD);
pad_stops[0] = pad_stops[1] = stops[0];
pad_stops[2] = pad_stops[3] = stops[n_stops - 1];
pad_stops[0].offset = 0;
pad_stops[3].offset = 1;
_cairo_ps_surface_emit_stitched_colorgradient (surface, 4, pad_stops);
} else if (n_stops == 2) {
/* no need for stitched function */
_cairo_ps_surface_emit_linear_colorgradient (surface, &stops[0], &stops[1]);
} else {
/* multiple stops: stitch. XXX possible optimization: regulary spaced
* stops do not require stitching. XXX */
_cairo_ps_surface_emit_stitched_colorgradient (surface, n_stops,stops);
_cairo_ps_surface_emit_stitched_colorgradient (surface, n_stops, stops);
}
_cairo_output_stream_printf (surface->stream,
"def\n");
@ -3250,6 +3275,21 @@ _cairo_ps_surface_emit_gradient (cairo_ps_surface_t *surface,
bounds_x1, bounds_y1,
bounds_x2, bounds_y2,
tolerance, domain);
} else if (pattern->stops[0].offset == pattern->stops[pattern->n_stops - 1].offset) {
/*
* If the first and the last stop offset are the same, then
* the color function is a step function.
* _cairo_ps_surface_emit_pattern_stops emits it as a stitched
* function no matter how many stops the pattern has. The
* domain of the stitched function will be [0 1] in this case.
*
* This is done to avoid emitting degenerate gradients for
* EXTEND_PAD patterns having a step color function.
*/
domain[0] = 0.0;
domain[1] = 1.0;
assert (pattern->base.extend == CAIRO_EXTEND_PAD);
} else {
domain[0] = pattern->stops[0].offset;
domain[1] = pattern->stops[pattern->n_stops - 1].offset;