Bug 483192

Summary:	Text and images are not properly scaled at 150% display scale
Product:	[Applications] Falkon	Reporter:	Kunshan Wang <wks1986>
Component:	general	Assignee:	David Rosca <nowrep>
Status:	REPORTED ---
Severity:	normal	CC:	demm, tim, vincenzo.romano
Priority:	NOR	Keywords:	qt6
Version First Reported In:	24.02.0
Target Milestone:	---
Platform:	Arch Linux
OS:	Linux
Latest Commit:		Version Fixed/Implemented In:
Sentry Crash Report:
Attachments:	Falkon browser at 150% display scale After upgrading to Qt 6.8.0 Window title bar

Description Kunshan Wang 2024-03-11 03:15:26 UTC

Created attachment 166929 [details]
Falkon browser at 150% display scale

SUMMARY

This happens after upgrading to KDE6.  I set my monitor to 150% scale.  But the web content I see in the Falkon browser seems to be zoomed badly, with text and image edges with uneven widths, as if it were zoomed using near-neighbour interpolation.

STEPS TO REPRODUCE
1. Open System Settings, go to "Display & Monitor", and set "Scale" to 150%
2. Open the Falkon browser
3. Open any web page (such as the default page https://www.falkon.org/)

OBSERVED RESULT

See the attached screenshot.  Characters are badly shaped, with unevenly thick and thin strokes.  The image is also a bit blurred. 

EXPECTED RESULT

The text should have sharp edges, and the image should not be that blurred.

SOFTWARE/OS VERSIONS
Operating System: Arch Linux 
KDE Plasma Version: 6.0.1
KDE Frameworks Version: 6.0.0
Qt Version: 6.6.2
Kernel Version: 6.7.9-arch1-1 (64-bit)
Graphics Platform: Wayland

ADDITIONAL INFORMATION

If I set "Scale" to 100%, the problem disappears.

This same problem also appears in the Angelfish browser.

This problem does not appear in the Firefox browser (running natively as a Wayland client) even if the "Scale" is set at 150%.

I am using the Plasma Wayland session.  If I invoke "falkon --platform xcb" on the command line, the text looks smoother.  But I am not sure whether it is aware of HiDPI and therefore renders directly at higher resolution, or it uses a smoother scaling algorithm.

Comment 1 Tim Carr 2024-03-11 07:28:23 UTC

I also notice similar distortion at 175% scale, so far I've only noticed within QtWebEngine views like Falkon, Konqueror, and Help Center. Looks like an upstream issue: https://bugreports.qt.io/browse/QTBUG-113574

Operating System: Arch Linux 
KDE Plasma Version: 6.0.1
KDE Frameworks Version: 6.0.0
Qt Version: 6.6.2
Kernel Version: 6.7.9-arch1-1 (64-bit)
Graphics Platform: Wayland

Comment 2 Kunshan Wang 2024-03-11 13:07:03 UTC

(In reply to Tim Carr from comment #1)
> I also notice similar distortion at 175% scale, so far I've only noticed
> within QtWebEngine views like Falkon, Konqueror, and Help Center. Looks like
> an upstream issue: https://bugreports.qt.io/browse/QTBUG-113574

Yes.  I see the same issue with Konqueror and Help Center, too.  The workaround mentioned in that link (`QT_SCALE_FACTOR_ROUNDING_POLICY=RoundPreferFloor`) works for me, too.  I think it is caused by that.

Comment 3 Tim Carr 2024-03-17 00:16:54 UTC

*** Bug 482825 has been marked as a duplicate of this bug. ***

Comment 4 Kunshan Wang 2024-10-15 03:17:07 UTC

Created attachment 174834 [details]
After upgrading to Qt 6.8.0

The attachment is what it looks like after upgrading to Qt 6.8.0

The "FALKON" logo on the top is an SVG and it is rendered perfectly.  The screenshot in the middle is a PNG, and at this window size it is scaled down.  I don't see any rough edges here.  The text on the bottom is also rendered properly.

I think the bug is fixed.

Comment 5 0BADC0DE 2024-10-15 07:49:57 UTC

I still get issues with window title.
It looks great on my 135% monitor, it looks awful on the 100% one.
I am not sure it is the same issue.

Comment 6 0BADC0DE 2024-10-15 07:50:41 UTC

Created attachment 174839 [details]
Window title bar

Plasma Version : 6.2.0-2
KDE Version : 24.08.2-1
Frameworks Version : 6.7.0-1
Qt6 Version : 6.8.0-1