Layout dimensions inside ScrollView not updated when increasing window size

[mgunyho]

Hi,

When a window with a ScrollView is resized to be bigger, the dimensions of the layout inside the ScrollView are apparently not updated, and the scrollbar extends outside of the ScrollView. As far as I can tell, this doesn't happen when the window becomes smaller. If I drag the slider, it snaps to the correct place.

Here's a minimal working example:

import { ScrollView } from "std-widgets.slint";

MainWindow := Window {
    preferred-width: 300px;
    preferred-height: 300px;
    ScrollView {
        HorizontalLayout {
            Rectangle {
                height: 500px;
                width: 500px;
                background: red;
            }
        }
    }
}

Here's a short video of it happening:

slint-scrollview-resize.2023-02-13.20-03.mp4

This happens both in debug and release version.

Possibly related to #2202 ?

Environment:

• Slint version: 0.3.4, also happens on master @ e557ba5
• Backend: winit-femtovg
• rustc: 1.66.1
• OS: OpenSUSE Tumbleweed with X11
• WM: KDE, also happens on i3 with Ubuntu 20.04

[ogoffart]

Thanks for the bug report.

Normally, the content-x and content-y property are set when the scrollbars are moved (or the wheel is rolled).
This process ensure that content-x and content-y are always within the bounds.
The problem is that when resizing, we don't change content-x and content-y. There is no way to express in the .slint language used by the widgets that they should be within the bounds because there can't be a binding since we change the value "manually" and we don't get callbacks when the geometry change.

Because the content position is not in bound, the computation of the size of the scrollbar is off.
We could fix the scrollbar being off by applying extra bounds in their binding, but that wouldn't fix the problem.

In other to fix this we either:

• Need a way to have a callback called when the geometry property changes: Have callback emitted when a property changes #112
• Or, Somehow do something in the Flickable native code to ensure that the content is in bounds.