Currently we use integers and do lots of calculations and recalculations resulting in rounding errors which mess up with text spacing specially at low resolution screens.
We should switch to using floats to store glyph positions instead, which would make the rounding errors less visible. It would also allow us to benefit from sub-pixel positioning support in the graphics libraries we use.
*** Bug 105936 has been marked as a duplicate of this bug. ***
My Bug 105936 report was moved here. Probably the right place. But here I read "earliest affected version 18.104.22.168 release".
Not true on MacOSX: All LO versions up to 5.2.5 have no problems with glyphs positioning, all work excellent.
This problem begun only with LO 5.3, and there it is on MacOSX massively. I had to downgrade to LO 5.2.5. It's not possible to work with this broken font display.
(On Linux and Windows this might be different.)
The problem is HarfBuzz, which was only introduced in LO 5.3. I hope this gets fixed soon.
The underlying issue is as old as this code base, it started showing up on Mac because we no longer use Core Text (which uses floats for glyph positions) and share the same code on all platforms.
I assume the "float" problem lies in the Firefox code, since HarfBuzz is used in Firefox and Chrome also, which have no problems with glyph display. Will this "float" bug be fixed anywhere soon?
*** Bug 106495 has been marked as a duplicate of this bug. ***
Sorry, my commentary from February had an error. It should read:
"I assume the "float" problem lies in the LibreOffice code and not in HarfBuzz, since HarfBuzz is used in Firefox and Chrome also, which have no problems with accurate glyph display. Will this "float" bug of LibreOffice be fixed anywhere soon?"
No one is currently working on this, feel free to work on it yourself or recruit someone to work on it.
Caolan may have fixed this here.
tdf#107249 round ascent/descent/extleading on conversion to int
(In reply to Yousuf Philips (jay) from comment #8)
> Caolan may have fixed this here.
> tdf#107249 round ascent/descent/extleading on conversion to int
That is a different issue.
*** Bug 113665 has been marked as a duplicate of this bug. ***
Do we have a (compact) API subset that needs to be changed from int to double to start the change?
(In reply to Mike Kaganski from comment #11)
> Do we have a (compact) API subset that needs to be changed from int to
> double to start the change?
I’d start with the “Text functions” section in include/vcl/outdev.hxx and go down and up from there.
We will need to switch from tools::Point, tools::Rectangle etc. to basegfx::B2DPoint, basegfx::B2DRectangle, not just int to float/double. May be using basegfx::B2IPoint first since they are still int-based, so the first round would focus on the difference in semantics and API between tools and basegfx, then next round would tackle the actual floating pint conversion.
For me it presents as a HiDPI bug, in that it's when desktop scaling is at 200%, 300%, text (any font) can be quite a reasonable editing size on screen but show this poor positioning of glyphs within each word, making it headache-inducing to look at, and actually a serious impediment to wanting to use the software. Of course it was there before, HiDPI just amplifies it, making it a problem at larger font sizes as displayed on screen.
As the worst problem is just the positioning of glyphs within words I looked for the code that does that. It seems to be mostly in vcl/source/gdi/CommonSalLayout.cxx, where the actual work is delegated to Harfbuzz, which appears to work in integers, but I think at a very high resolution (whatever a upem is). The values that then come out of that then have a scale applied at double, rounded, and I suspect subject to more scaling later, in particular with respect to the desktop scaling factor in HiDPI modes. And that's probably where it's going wrong.
I had a play with trying to fix things locally in here and in vcl/source/gdi/sallayout.cxx, changing all the glyph positioning code to use doubles (and B2DPoint etc), including changing GlyphItem (sallayout.hxx) to use those types for its positions, widths and offsets and rounding as necessary at the edges of that, but I did rather get lost in the weeds, specifically, where to find the edges of it, to minimise the disruption to the rest of the codebase.
I suspect a fix can't really be confined like that, and it's probably undesirable anyway. It looks like we'd probably want to make DeviceCoordinate a double (as controlled in config_host/config_vcl.h.in showing this has been at least partially prepared-for) and follow *everywhere* that leads, one such place being the text functions in outdev.hxx of course.
Then final rounding to integers for actual pixels on screen would probably want to happen in platform specific code. As absolutely late as possible, at the moment of output, anyway. Then if and when there's a platform that takes double coordinates that rounding simply doesn't have to happen there.
Regarding the suggestion of going via B2IPoint and friends as an intermediate step towards B2DPoint and friends, I note that the B2I types are carefully defined to use 32-bit ints (sal_Int32), whereas Point, Rectangle et al use long (which let's face it *is* 64-bit almost everywhere that matters now) as does much existing position-calculating code. So I'd worry that we'd be setting ourselves up for a fight to resolve issues relating to that loss of range when it's only needed as an intermediate step.
... All of which would be an absolutely gigantic changeset, no wonder no-one who knows the code wants to do it! The more I poked around in this the more I thought, "Oh God, no..." and "Can we *really* not localise this fix in sallayout?" :-) But no, ultimately changing *all* the device coordinate code to double is probably what has to happen one day.
Another thought I had, noticing that in OpenOffice.org Writer on a 4K screen of course has no HiDPI awareness to speak of, so its user interface is unusable, but zoom in on the text to an editing size and it looks fine - at 240% zoom you would expect that, of course. Pretty much the same applies in LibreOffice Writer if you set your desktop scaling to 100% on a 4K screen. So I wondered, what if instead you just *not* apply desktop scaling on the document view panes/frames whatever they're called here, and, um, *lie* on the user interface, ie: multiply the user selected zoom by the desktop scaling factor? :-)
Another alternative to floating point, is to keep using integers but use a scale, so instead of shaping at 10 pixels and drawing at the coordinates we get, we shape at 10 * SCALE and shape ant coordinates / SCALE. Which is what many other libraries do, and I vaguely remember that we have something similar by may be we are not using it thoroughly. Worth investigating.
*** Bug 108484 has been marked as a duplicate of this bug. ***
Alexander Farrow committed a patch related to this issue.
It has been pushed to "master":
tdf#103322 GlyphItem::m_aLinearPos use getX() instead of X()
It will be available in 6.3.0.
The patch should be included in the daily builds available at
https://dev-builds.libreoffice.org/daily/ in the next 24-48 hours. More
information about daily builds can be found at:
Affected users are encouraged to test the fix and report feedback.
I'm the reporter of bug 113665 which was marked as a duplicate of this bug.
I have tried the following daily builds but the problem described in bug 113665 is still present:
So, maybe that bug is actually not related to this bug?
(In reply to horus from comment #17)
> I'm the reporter of bug 113665 which was marked as a duplicate of this bug.
> I have tried the following daily builds but the problem described in bug
> 113665 is still present:
> * libo-master64~2019-05-22_00.57.02_LibreOfficeDev_22.214.171.124.alpha1_Win_x64.msi
> * libo-master64~2019-05-29_09.41.50_LibreOfficeDev_126.96.36.199.alpha1_Win_x64.msi
> So, maybe that bug is actually not related to this bug?
Please revisit after this report is marked RESOLVED FIXED
(In reply to horus from comment #17)
> So, maybe that bug is actually not related to this bug?
It remains the same, the commit in comment 16 is only a part  of what will be a major refactoring--functionally nothing has changed yet in composing what displays.
Hang in there!
(In reply to Buovjaga from comment #18)
> Please revisit after this report is marked RESOLVED FIXED
(In reply to V Stuart Foote from comment #19)
> It remains the same, the commit in comment 16 is only a part  of what
> will be a major refactoring--functionally nothing has changed yet in
> composing what displays.
> Hang in there!
I also noticed this bug and finally found this thread... Two points from my side: First, I do not really understand how this is a desktop scaling / HiDPI bug? For me this would mean that at 100% desktop scaling this issue should not appear, or am I wrong here? I also tested two different Full HD screens and an old 1280x1024 screen that all use desktop scaling 100% (here I'm referring to the 100% scale that can be configured under Windows' screen properties) - and the issue is definitely visible. How can this happen if it is a HiDPI issue?
And then my second question, where I'm especially referring to Rachel's comment. I didn't look into the code, but if the whole coordinate stuff has to be migrated from int to float (or double), wouldn't it be a feasible approach to start with changing "only" any involved variable definition from int to float as a first step, without changing anything else? So we would only save our ints in float-valued variables (maybe introducing implicit cast warnings) but once done, the positioning code could be migrated step by step to fully support float?
Also hoping this issue gets fixed soon. Especially for Impress presentations it can really be a show stopper if the slides are not properly rendered...
Changing enhancement priority to 'high' since the number of people in CC is higher than 20
Created attachment 157431 [details]
Artifact when scrolling text
Adding this image to this bug because the one I opened depends on it. It shows an artifact that I get when I scroll a document: text gets deformed, with elongated characters, often unaligned. I think it's related to the problem with using integers rather than floating points for glyph positioning.