Bug 426488

Summary:	Large fonts incurs cursor movement lag
Product:	[Frameworks and Libraries] frameworks-ktexteditor	Reporter:	Björn Lindqvist <bjourne>
Component:	general	Assignee:	KWrite Developers <kwrite-bugs-null>
Status:	RESOLVED NOT A BUG
Severity:	normal	CC:	cullmann, nate
Priority:	NOR
Version:	5.74.0
Target Milestone:	---
Platform:	Arch Linux
OS:	Linux
Latest Commit:		Version Fixed In:

Description Björn Lindqvist 2020-09-13 15:44:25 UTC

I have a HiDPI screen and poor vision so I use large fonts. Using editors like Kate and Kwrite with the font Times New Roman at size 12 works fine. But when I change the font size to 32, cursor movement becomes significantly lagged. Even without scrolling. There is no reason why cursor movement should be much slower when using large fonts.

Comment 1 Christoph Cullmann 2020-09-15 16:35:07 UTC

Hmm, I have some 4k screens here, too.
Works fine for me.
But I have seen similar slowness on some other machine with the Nvidia driver.
Which driver to you use (and which kind of graphics card?)

Comment 2 Nate Graham 2020-09-15 18:36:28 UTC

FWIW I also have a 4K screen and use a 250% scale factor and I don't experience any cursor slowness with large font sizes.

Comment 3 Björn Lindqvist 2020-09-30 20:59:03 UTC

Can you try with text with BIG fonts? Times New Roman with point size 24 works fine for me, but at 48 it becomes extremely sluggish. The card I'm using is Intel Corporation HD Graphics 5300 with the default driver.

Comment 4 Christoph Feck 2020-10-06 04:20:58 UTC

Qt probably disables caching for large font sizes.

Comment 5 Christoph Feck 2020-10-06 04:23:17 UTC

> I have a HiDPI screen and poor vision so I use large fonts.

Workarounds:
- use global scaling, instead of only changing the font size
- switch to a lower resolution (if you have poor vision, you probably won't see a difference)

Comment 6 Christoph Cullmann 2021-06-12 19:31:26 UTC

Sorry, if this really is an issue for you, you can try to report this upstream to Qt, but in KTextEditor/Kate/... we can't improve the speed of the text rendering operations.

Or you might try the advice given below to use a smaller resolution.

Comment 7 Björn Lindqvist 2021-06-12 20:11:25 UTC

(In reply to Christoph Cullmann from comment #6)
> Sorry, if this really is an issue for you, you can try to report this
> upstream to Qt, but in KTextEditor/Kate/... we can't improve the speed of
> the text rendering operations.
> 
> Or you might try the advice given below to use a smaller resolution.

I wouldn't have reported it unless it was an issue for me so you didn't have to add the "really" qualifier. The suggested workarounds doesn't work as they make the whole screen blurry.