Click on mouse-button-press (button-down)

[emilk]

egui currently register clicks when the mouse button is released (button-up). Having the clicks register on press instead would make egui feel a lot more responsive.

EDIT: let's make this globally configurable in Style

Clicks vs drags

If the area under the pointer responds to both click AND drags, we cannot immediately know if a mouse press is going to turn into a click or a drag. This means we cannot do click-on-press in these situations. Only when the surface under the pointer responds ONLY to clicks can be do this.

To ensure most surfaces are either click XOR drag we should fix two things:

• Disable drag-to-scroll on non-touch-screens
• Disable drag-to-move for egui::Window on non-touch-screens

Drag-to-abort

With click-on-press you cannot abort a click midway. This is arguably a slight disadvantage.

[lucasmerlin]

I'd love if this was optional. In my painting app, people might accidentally start dragging on some widget during fast painting. Currently those interactions would just be cancelled, with click on press this might get annoying.

[Mingun]

Having the clicks register on press instead would make egui feel a lot more responsive.

I don't think this is a good idea. (Almost) every application register clicks on button up. Just try to press any button / link on this page (New issue for example) and wait any time. Then release the button. Only after that a new issue page will open (checked in Firefox).

Another example -- try to close window by cross button (on Windows). Window is closed only on button release and (this is important) only if the release occurred within the button. This allows you to opt out of pressing if you pressed by accident, simply by moving the mouse cursor outside the button. Every other button on Windows behaves like that.