Fix scroll handle extending outside of ScrollArea

[gilbertoalexsantos]

• I have followed the instructions in the PR template
• Closes ScrollArea's scrollbar goes past frame's borders #3734

Info

This PR addresses an issue where resizing a scroll handle can lead to unwanted overlap.

It is also happening on the egui-demo.

Cause

Note: The following explanation assumes a vertical scroll; however, the logic applies equally to horizontal scrolling.

When the scroll handle is positioned at the top or bottom of the scroll area and the handle is resized to fit the minimum handle size, there is a risk of overlap. This occurs if the handle’s new size extends beyond the bounds of the scroll area.

Proposed Solution

1. Check whether increasing the handle size will cause it to overlap with the scroll area.
2. If an overlap is detected, adjust the handle’s center position by the overlap amount, moving it towards the center of the scroll area.

[github-actions]

Preview available at https://egui-pr-preview.github.io/pr/5286-fix-scroll-handle-overlap
Note that it might take a couple seconds for the update to show up after the preview_build workflow has completed.

[lucasmerlin]

While this is a improvement, now it will look like you're at the top while already scrolled done by some amount:

Bildschirmaufnahme.2024-10-20.um.17.22.48.mov

Ideally, the scrollbar position would just be calculated correctly, taking the min size into account.

[gilbertoalexsantos]

@lucasmerlin

Oh, you're totally right. I didn't notice this behaviour 🥲

I'll work on a fix for this ☺️

[gilbertoalexsantos]

@lucasmerlin

I did an update to the PR.

1º - I extracted the handle_rect calculation to a function
2º - When calculating the handle position, I take into consideration the handle size (by subtracting it from scroll_bar size)

scroll_use.mp4

[lucasmerlin]

Awesome, it's working perfectly now, thank you for this! 🚀 I think we can merge this once the pipeline succeeds.

[gilbertoalexsantos]

I did two more commits:
1º - Applying rustfmt (ops)
2º - Removing unused import

[lucasmerlin]

Seems like you'll need to do another format. Usually it makes more sense to run rustfmt last after any other changes

[gilbertoalexsantos]

Indeed.

I'm using RusRover, and for some reason, the format is different than: cargo fmt. Maybe they are using some format of their own.

[lucasmerlin]

Assuming you mean RustRover, there is a setting to use rustfmt instead:

Not sure why they don't enable this by default 🤔

[gilbertoalexsantos]

Oh... That is nice. I'll toggle it. Thank you ^^