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<b><a class="bz_bug_link
bz_status_NEW "
title="NEW - text failing to display on SVG and X11 surface even though it works correctly on PDF and PS surfaces"
href="https://bugs.freedesktop.org/show_bug.cgi?id=104042#c5">Comment # 5</a>
on <a class="bz_bug_link
bz_status_NEW "
title="NEW - text failing to display on SVG and X11 surface even though it works correctly on PDF and PS surfaces"
href="https://bugs.freedesktop.org/show_bug.cgi?id=104042">bug 104042</a>
from <span class="vcard"><a class="email" href="mailto:psychon@znc.in" title="Uli Schlachter <psychon@znc.in>"> <span class="fn">Uli Schlachter</span></a>
</span></b>
<pre>Actually... what are the semantics of drawing an alpha-only surface to a
color-only target with operator OVER? I'm not quite sure and this seems to be
the root of the problem. <a href="https://www.cairographics.org/operators/">https://www.cairographics.org/operators/</a> doesn't
answer this either.
I noticed that with cairo-xcb the example program works, while with cairo-xlib
still nothing is displayed. After staring at protocol traces for far too long,
I noticed that the significant difference seems to be in the drawing to the
intermediate surface:
cairo-xlib:
- creates an uninitialized(???) intermediate pixmap
- draws the glyphs to it via operator OVER
- with a black solid source
cairo-xcb:
- creates an intermediate pixmap and clears it
- draws the glyphs to it via operator ADD
- with a white solid source
Both backends then OVER this intermediate to the target picture which uses a
RGB24 format. I'm not actually sure why this produces no result with
cairo-xlib, but the missing clearing of the intermediate pixmap strikes me as
quite odd.</pre>
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