[Konsole-devel] [konsole] [Bug 350651] New: Konsole has scrolling artifacts if HiDPI screen with scaling in Qt

[Christoph Cullmann]

https://bugs.kde.org/show_bug.cgi?id=350651

            Bug ID: 350651
           Summary: Konsole has scrolling artifacts if HiDPI screen with
                    scaling in Qt
           Product: konsole
           Version: master
          Platform: Compiled Sources
                OS: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: NOR
         Component: general
          Assignee: konsole-devel at kde.org
          Reporter: cullmann at kde.org

On a HiDPI screen if the Qt scaling of output is active, you get ugly scroll
artifacts.

A quickfix for this is to disable the shortcut for the scrolling if
transparency is on (if you disable transparency on the commandline via
--notransparency the same effect is archived).

Hack:

void TerminalDisplay::updateImage()
{
    if (!_screenWindow)
        return;

    // optimization - scroll the existing image where possible and
    // avoid expensive text drawing for parts of the image that
    // can simply be moved up or down
    if (!WindowSystemInfo::HAVE_TRANSPARENCY && _wallpaper->isNull()) {
        scrollImage(_screenWindow->scrollCount() ,
                    _screenWindow->scrollRegion());
        _screenWindow->resetScrollCount();
    }

Could be perhaps improved by checking if scale factor != 1.

Would such a quickfix be acceptable? ATM konsole is not really usable on a
hidpi screen with the artifacts ;=)

Reproducible: Always

Steps to Reproduce:
1. export QT_DEVICE_PIXEL_RATIO=2
2. start Konsole (with some recent enough Qt >= 5.4
3. scroll => artefacts

Actual Results:  
Artefacts during scrolling

Expected Results:  
Should just scroll ;=)

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