[Poppler-bugs] [Bug 95485] [patch] add support for subpixel rendering support for cairo backend

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=95485

--- Comment #3 from Adrian Johnson <ajohnson at redneon.com> ---
(In reply to Yichao Zhou from comment #2)
>It seems that cairo uses other blend mode other than
> CAIRO_OPERATOR_OVER to create a cairo_t as the canvas for input of user
> defined render function.  So if we enable subpixel rendering, the result
> will be incorrect.

Where does this happen? Looking at cairo-user-font.c:

In _cairo_user_scaled_glyph_init, a recording surface is created. A context is
created for the recording surface. The default operator is not changed. The
user render function is called to record the glyph drawing operations.

In _cairo_user_scaled_glyph_init, when the glyph bitmap is requested, an image
surface is created. If the font antialias option is subpixel the image will be
ARGB32. The recording is replayed to the image surface.

If you are seeing a problem with type 3 fonts you should be able to provide a
sample pdf file and screen shots of the incorrect rendering. pdftocairo has
-antialias option that can also be used to for testing.

This sound like a separate issue to your proposed feature and should be filed
in a separate bug. If may actually be a cairo bug and it would be helpful if
you could create a test that used cairo to demonstrate the bug. We don't want
to add code to poppler to workaround a cairo bug. Instead the bug should be
fixed in cairo.

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