fix: avoid CentralPanel overflowing in a window

[avalsch]

use eframe::egui;

fn main() -> eframe::Result<()> {
    eframe::run_simple_native("window overflow", Default::default(), |ctx, _| {
        egui::Window::new("window overflow").show(ctx, |ui| {
            egui::CentralPanel::default().show_inside(ui, |ui| {
                ui.label("Hello, World");
            });
        });
    })
}

Old behavior:

New behavior:

I'd ideally add a test for this but I'm not sure how to go about doing that.

• Closes CentralPanel overflows in a window unless there is a Top, Bottom or Right pannel #901
• I have followed the instructions in the PR template

[github-actions]

Preview available at https://egui-pr-preview.github.io/pr/7042-window-panel-overflow
Note that it might take a couple seconds for the update to show up after the preview_build workflow has completed.

[lucasmerlin]

Thanks for the fix! To add tests, the easiest would be to add a new kittest test to tests/egui_tests, the test could just simply be a screenshot test with the repro you provided.

[lucasmerlin]

I think instead of ui.new_child we could also do ui.scope_builder which should do the expand_to_include_rect for us. Might be a bit cleaner.

[avalsch]

It seems to me like scope_builder doesn't preserve the same behavior with set_clip_rect. This might break some things, but I'm not sure?

[avalsch]

Regarding using scope_builder rather than new_child, the other panel implementations (SidePanel, TopBottomPanel) also use new_child. Is this something we would want to change?