Native scrollbars decrease smooth scrolling performance

[equeim]

QupZilla 2.1.1, Arch Linux. When native scrollbars are enabled, smooth scrolling is not so smooth, looks like like 30 fps.

[Vistaus]

Can't reproduce this on Solus. What are your hardware specs and are you running any other apps when you notice this? If so, which ones?

[equeim]

Video card is AMD Radeon R9 280X, OpenGL driver is radeonsi from Mesa 17.0.1, xf86-video-ati 7.8.99. The issue is present regardless of if I run any other apps.

I also have this issue on Windows 10.

[nowrep]

I can reproduce it, you can enable FPS counter in web inspector and it's clear that it is locked to 30fps. The problem is rendering the scrollbars (probably because QtWebEngine is QQuickWidget and that doesn't mix well with QtWidgets performance-wise), but I have currently no idea how to fix it.
I guess I'll need to disable the native scrollbars by default (or even completely remove this feature).

...(or even completely remove this feature).

I'll be so happy if you do it!

[nowrep]

You can disable it if you don't like it.

Ooops, i didn't read carefully, i thought you are talking about „Smooth scrolling“

[equeim]

probably because QtWebEngine is QQuickWidget and that doesn't mix well with QtWidgets performance-wise

AFAIK, QWebEngineView is QWidget.

[nowrep]

AFAIK, QWebEngineView is QWidget.

Not under the hood, it was QOpenGLWidget before and is now QQuickWidget to share the same code as QtQuick version.

https://code.qt.io/cgit/qt/qtwebengine.git/tree/src/webenginewidgets/render_widget_host_view_qt_delegate_widget.cpp

[vtronko]

I double this.

[nowrep]

It's now disabled by default.

[kkofler]

IMHO, it would be a better idea to disable smooth scrolling by default and keep native scrollbars enabled by default if the 2 features conflict.

[iondissonance]

@kkofler +++

[nowrep]

No, it wouldn't be better. It doesn't affect only smooth scrolling, but the whole rendering. If the scrollbars are redrawn (because the scroll position changed), it halves the frame rate of the whole webview. So, even though it is most visible during smooth scrolling, it will affect also pages that implements smooth scrolling with javascript, ...

Unless I fix the main issue, it will stay as it is (native scrollbars disabled by default).