GTK scrollable seems to misbehave compared to WPF/mac

[philstopford]

Expected Behavior

Add scrollbars when content is out of view.

Actual Behavior

No scrollbars under GTK

Steps to Reproduce the Problem

1. From https://github.com/philstopford/Quilt_GPL, grab a GTK and/or WPF release or the code (in which case, you'll also need https://github.com/philstopford/DesignLibs_GPL). The projects expect .NET 5 to build.
2. Run the WPF if you need a reference. Select a shape from the menu in the middle, and you should see a UI of the form :

Notice the scrollbars when content is out of view, and resizing panels, or the application window has a corresponding effect on the scrollbars.

3. Run the GTK version. No scrollbars show up :

Code that Demonstrates the Problem

Repositories above; will work on a smaller test case if desired.

Specifications

• Version:
• Platform(s): Gtk3
• Operating System(s): Ubuntu 21.04

[cwensley]

Hey @philstopford, thanks for submitting the issue! On some GTK themes the scrollbar only appears when you scroll or move the cursor near the scroll area.. This isn't the case, is it?

[philstopford]

It doesn't appear to be. I have to resize the window to see the out-of-view controls.

[cwensley]

@philstopford cool, just wanted to check. I'll take a look! .. and get to that Veldrid issue soon too..

[philstopford]

OK. So it looks like a VMware install of Kubuntu does show the scrollbars when I hover over them, but for some reason this isn't behaving consistently with other platforms - the progress bar and label are out-of-view, rather than pinned at the bottom of the window. The scrollable is moving the full content of the left panel :

[cwensley]

Ok, so I got some time to look into this. The main problem was the top level scrollable was expanding its content to fit everything even though you have set a desired height of 270 for the settings panel. So even though it didn't appear like the scrollbar was there, it was in fact there only if you scrolled down to the very bottom of the main panel, as it is a separate scrollable.

The main culprit of this issue was that the OnGetPreferredHeightForWidth method needed to be overridden like OnGetPreferredHeight is.

[philstopford]

@cwensley : great - thank you for digging into this and fixing it up!