[cairo-bugs] [Bug 101866] raster source pattern callback weirdness

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=101866

--- Comment #1 from Uli Schlachter <psychon at znc.in> ---
Use cairo_raster_source_pattern_set_callback_data() to set the closure argument
of your callback:
https://www.cairographics.org/manual/cairo-Raster-Sources.html#cairo-raster-source-pattern-set-callback-data

The pattern argument is a static, stack-allocated copy that cairo creates
internally. I have to admit that I am not sure why this pattern is given to the
callback at all. The backtrace for the creation of the copy looks like that (I
guess that both calls create copies of the raster pattern):

Breakpoint 2, _cairo_pattern_init_static_copy
(pattern=pattern at entry=0x7fffffffe690, other=other at entry=0x55555575aab0) at
cairo-pattern.c:368
368     {
(gdb) bt
#0  _cairo_pattern_init_static_copy (pattern=pattern at entry=0x7fffffffe690,
other=other at entry=0x55555575aab0) at cairo-pattern.c:368
#1  0x00007ffff7aa7552 in _cairo_gstate_copy_pattern (original=0x55555575aab0,
pattern=0x7fffffffe690) at cairo-gstate.c:937
#2  _cairo_gstate_copy_transformed_pattern
(pattern=pattern at entry=0x7fffffffe690, original=0x55555575aab0,
ctm_inverse=ctm_inverse at entry=0x55555575a690, gstate=<optimized out>)
    at cairo-gstate.c:946
#3  0x00007ffff7aa9346 in _cairo_gstate_copy_transformed_source
(pattern=0x7fffffffe690, gstate=0x55555575a540) at cairo-gstate.c:973
#4  _cairo_gstate_paint (gstate=0x55555575a540) at cairo-gstate.c:1063
#5  0x00007ffff7a978ca in INT_cairo_paint (cr=0x55555575a510) at cairo.c:2221
#6  0x0000555555554d9f in draw (cr=0x55555575a510) at test.c:50
#7  0x0000555555554dea in main () at test.c:65
(gdb) cont
Continuing.

Breakpoint 2, _cairo_pattern_init_static_copy
(pattern=pattern at entry=0x7fffffffe3d0, other=other at entry=0x7fffffffe690) at
cairo-pattern.c:368
368     {
(gdb) bt
#0  _cairo_pattern_init_static_copy (pattern=pattern at entry=0x7fffffffe3d0,
other=other at entry=0x7fffffffe690) at cairo-pattern.c:368
#1  0x00007ffff7a9e59f in _cairo_composite_reduce_pattern (dst=0x7fffffffe3d0,
src=0x7fffffffe690) at cairo-composite-rectangles.c:56
#2  _cairo_composite_rectangles_init (clip=0x0, source=0x7fffffffe690,
op=<optimized out>, surface=0x55555575a380, surface at entry=0x7fffffffe690,
extents=0x7fffffffe350, 
    extents at entry=0x7fffffffe2f0) at cairo-composite-rectangles.c:97
#3  _cairo_composite_rectangles_init_for_paint
(extents=extents at entry=0x7fffffffe350, surface=surface at entry=0x55555575a380,
op=<optimized out>, source=0x7fffffffe690, clip=0x0)
    at cairo-composite-rectangles.c:122
#4  0x00007ffff7a9f8ae in _cairo_compositor_paint (compositor=0x7ffff7dd7320
<spans>, surface=0x55555575a380, op=<optimized out>, source=<optimized out>,
clip=<optimized out>)
    at cairo-compositor.c:55
#5  0x00007ffff7b0e391 in _cairo_surface_paint (surface=0x55555575a380,
op=op at entry=CAIRO_OPERATOR_OVER, source=0x7fffffffe690, clip=0x0) at
cairo-surface.c:2120
#6  0x00007ffff7aa9294 in _cairo_gstate_paint (gstate=0x55555575a540) at
cairo-gstate.c:1067
#7  0x00007ffff7a978ca in INT_cairo_paint (cr=0x55555575a510) at cairo.c:2221
#8  0x0000555555554d9f in draw (cr=0x55555575a510) at test.c:50
#9  0x0000555555554dea in main () at test.c:65


For this bug report: I would argue that your expected behavior just is not the
behavior that cairo provides, so there is no bug here. I'm not sure what you
mean exactly with "it is dead, so doing anything with it crashes". Your example
program does not crash here.

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