pygobject
How can I activate subpixel positioning for text with `pangocairo` and `pycairo`?
I am not sure if this is the right place to ask ... My apologies if I am wrong here.
I just came across this article saying that subpixel positioning was added to pango 1.44 in 2019 - not without its issues though. Apparently it is switched off by default. Both articles go as far as saying that the latest master from cairo is needed. Maybe it has been released in the meantime (?).
Two questions actually:
- Which version / release of
cairo&pycairodo I need for activating this feature? Or do I (still) need to buildcairo&pycairofrom (unreleased) master? - How do I activate subpixel positioning with
pycairo&pangocairo?
(I also posted this question on stackoverflow.)
cairo hasn't had a release since then. I don't know the current status of all this, sorry.
(the only thing I do know is that it's still broken on Windows, with master of everything)
(the only thing I do know is that it's still broken on Windows, with master of everything)
Which cairo backend are you using? Is that cairo-win32?
It seems like this is only supported on cairo-image and cairo-xlib (run in a (not up-to-date) git checkout of cairo):
$ git log | grep -5 'Support subpixel positionin'
commit e4a79db0108be6a2b06dfce51a44bcbdead66ebd
Author: Matthias Clasen <[email protected]>
Date: Sat May 25 00:35:04 2019 +0000
xlib compositor: Support subpixel positioning
As for the image compository, support a 4x4
subpixel grid.
commit 6fd4222ab00c3b93f038172a8c9d48375c5f86f0
--
commit ea9329215d3431ded51a71b724baf0edc25ad633
Author: Matthias Clasen <[email protected]>
Date: Sat Jul 28 12:25:47 2018 +0000
image compositor: Support subpixel positioning
Support subpixel positioning with a 4x4 subpixel grid.
When compositing glyphs in the image compositor,
we store the subpixel phases in the high bits of the
glyph index. The _cairo_scaled_glyph_index() macro
has been updated to discard these bits. By storing
Which cairo backend are you using? Is that cairo-win32?
Sorry, this was just a tiny rant and not cairo's fault (well, somewhat), and not related to subpixel rendering. Newer pango doesn't send pixel aligned coordinates for characters to cairo any more and cairo then tries to align them, but only does so badly because it is missing any context, leading to random character spacing. The fix would be to support subpixel rendering in the win32 backend, but that would mean using a different win32 API.
Gotta love those drive-by contributions to OSS projects that do exactly enough for their own use case instead of implementing things properly for everyone. :-) This makes me wonder what Pango did differently than cairo does now. Apparently just rounding each individual glyph position is not the answer.
@s-m-e Your answer seems to be "whatever Pango version @lazka is using automatically uses subpixel positioning with cairo, whether cairo supports that or not" and "cairo does not support it yet".
@s-m-e Your answer seems to be "whatever Pango version @lazka is using automatically uses subpixel positioning with cairo, whether cairo supports that or not" and "cairo does not support it yet".
I do not entirely understand what you're trying to say. I basically do not want to blame anyone. It is (was?) my understanding that this feature requires symmetrical support from both pango and cairo. So from a distance it looks like "feature is now part of pango releases, but a corresponding cairo release is missing at this point".
"feature is now part of pango releases, but a corresponding cairo release is missing at this point".
Yup, that's also my understanding. Sorry for my mis-communication.
(I didn't want to sidetrack this, so I've hidden the win32/pango comments. I hope that's ok)