slint-ui
`Slider` needs start callback
In my app, I'm updating a preview whenever the built-in Slider widget's changed callback is called and stopping the preview when its released callback is called. However, it would be better (when using the mouse) if the preview was started as soon as the user pressed down on the slider, even if the value wasn't changed yet. So, some new callback that was called at this point in the process would be useful. Surely, it should also be called when using the keyboard.
Button has a pressed (out) property
Similarly, we could add a pressed property to the Slider. Would that help?
The preview involves Rust code starting something that runs in another thread. On changed and released, I call a callback. I don't think an out-property would currently suffice, as long as change callbacks aren't available.