[cairo-bugs] [Bug 10301] LCD filtering patch

[bugzilla-daemon at freedesktop.org]

http://bugs.freedesktop.org/show_bug.cgi?id=10301





--- Comment #80 from Nicolaus L Hepler <nlhepler at gmail.com>  2009-01-25 23:09:24 PST ---
Bob,

Can you open up and look at the version of cairo used by ubuntu, and apply the
04_lcd_filter.dpatch?

In _fill_xrender_bitmap, look at the section near the end, where it converts
vertical RGB into ARGB32. There is a weird #if 1 #else #endif block in this
particular section, and I think this is where the problem is. I think the code
in the #else block is the correct code, and changing the #if 1 to #if 0 in the
04_lcd_filter.dpatch might fix it. (you'll need either a copy of the
libcairo2-2ubuntu1 source to compile from or you'll need to revert the patch.
There's some other stipulations about compiling that you might already know,
like you can't have the original gzipped or bzipped tars of the source in the
parent directory, or the devscipts will use them to build from.)

If anyone else is enlightened as to the math this is trying to perform, and can
tell me for sure that I'm wrong about this particular section screwing up, I
will gladly listen (and learn).

Sylvain, can you look into this? I don't have a platform handy for looking up
their most obvious use case in Compiz, and I can't get Firefox to do what they
say on a couple handy examples.

It would be nice to have this fixed as well as getting a working version of the
fallback patch finally upstream. I wish my time wasn't so spotty, but it would
also be encouraging to hear from either Behdad or Carl. I know Cairo is a
cross-platform tool, and these guys have to worry about other things cropping
up elsewhere, but these patches really help usability for some of the linux
guys. I know Behdad isn't fired up about this issue, but you, Brandon, and I at
least see a point to getting these patches upstream in some acceptable form.

Nicolaus (Lance)

(In reply to comment #78)
> Ubuntu has included this patch, for some reason, and it causes a problem with
> drawing black-on-black text sometimes when VRGB subpixel smoothing is selected.
>  The ubuntu bug is:
> 
> https://bugs.launchpad.net/ubuntu/+source/cairo/+bug/145604
> 
> It appears there might be a byte-shift problem in this patch.
> 


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