No lightweight way to adjust ui style

[vkkoskie]

I could be wrong about the following. I'm just starting to learn Rust, so I could have misunderstood something. I believe this is the only way to change style elements given the current API:

let mut style = ui.style().clone();
style.item_spacing = egui::vec2(x, y);
ui.set_style(style);

The ui's style member is private and the ui.style() method returns an immutable reference. So the only way to change a single style element is to clone the whole struct out, make the change, and pass ownership back into the ui. This is awkward to implement, and forces needless copies. It's also redundant with the clone that happens when a child ui is created. Touching a given ui's style won't affect global style settings.

The patterns in the Style::ui widget hints that some kind of public access is safe and may have been intended, but I can't find a pathway for it.

[emilk]

Good point! I think allowing ui.style_mut().item_spacing = vec2(x, y); would make sense.

[vkkoskie]

Great! PR submitted. After submitting the initial comment, I noticed the same thing about ui.layout. The PR includes both changes. Sorry if that's bad form.