[feature request] A widget that sets the cursor on hover.

[richard-uk1]

Currently if you want to set the cursor for a widget you need to intercept events. This means using a custom Controller, which can be fiddly and error-prone.

This request involves adding a new widget (probably called Cursor) to druid::widget that sets the cursor whenever it is hovered, and a cursor method to WidgetExt that wraps the widget in a Cursor.

[richard-uk1]

I'll wait for people to comment on whether it's a good idea before I say people should have a go at implementing it.

[richard-uk1]

Here's a controller I made to do something like this. It's probably better to use a Controller rather than a Widget, but I'm not 100% sure this is correct:

/// Button controller.
///
/// Responsible for setting the cursor and calling a contained on_click function on click.
struct BtnController<T> {
    cursor: Cursor,
    on_click: Box<dyn Fn(&mut EventCtx, &mut T, &Env)>,
}

impl<T> BtnController<T> {
    fn new(cursor: Cursor, on_click: impl Fn(&mut EventCtx, &mut T, &Env) + 'static) -> Self {
        BtnController {
            cursor,
            on_click: Box::new(on_click),
        }
    }
}

impl<T, W: Widget<T>> Controller<T, W> for BtnController<T> {
    fn event(&mut self, child: &mut W, ctx: &mut EventCtx, event: &Event, data: &mut T, env: &Env) {
        match event {
            Event::MouseMove(_) => ctx.set_cursor(&self.cursor),
            Event::MouseDown(MouseEvent { buttons, .. }) if buttons.has_left() => {
                ctx.set_active(true)
            }
            Event::MouseUp(MouseEvent { buttons, .. }) if !buttons.has_left() => {
                if ctx.is_active() {
                    (*self.on_click)(ctx, data, env);
                    ctx.set_active(false);
                }
            }
            _ => (),
        }
    }
}

a Cursor widget wouldn't need the on_click callback, so would be simpler.

[jneem]

Do the changes in #1433 help here? I think they should give more-or-less the behavior you want without adding wrapper widget...

[richard-uk1]

@jneem say I have a widget like Flex::row().with_child(Label::new("test")), how do I make the cursor change on hover?

[jneem]

Oh, right, I was thinking of the case where you already have a custom widget.

What if we added set_cursor to the lifecycle context, and then added a on_added function to WidgetExt, allowing for a callback that's called when the widget gets WidgetAdded? I can imagine this being useful for other purposes, and it would allow you to do

Flex::row()
    .with_child(Label::new("test"))
    .on_added(|ctx, _data, _env| ctx.set_cursor(&Cursor::Arrow));

[richard-uk1]

Hmm yeah that would work as well. So this is a custom controller that runs the callback on LifeCycle::WidgetAdded, with a helper function?

[jneem]

That's what I was thinking, yes. If there are other things that are worth having callbacks for, they could be included as well, of course.

[richard-uk1]

Cool, then if we wanted then we could add a WidgetExt::with_cursor function on top. Sounds like a (more general) plan.

@cmyr or @raphlinus what do you think about a WidgetExt function that allows you to do something on LifeCycle::WidgetAdded (called e.g. WidgetExt::on_added)? And how about a WidgetExt::with_cursor to set the cursor (a special case of WidgetExt::on_added)?

[cmyr]

I think this makes a lot of sense!

(I think that on_added is a very strong idea, and i think on_cursor makes sense too, although it does seem like it can be implemented pretty easily as part of on_added so it doesn't feel like as clear a win. on_added feels like a big win!)

[richard-uk1]

Ok sounds like just adding on_added for now is the consensus. I'll update the issue.

Edit: probably makes sense to create a new issue. I want it to be a "good first issue" kinda issue, so someone new could implement it if they so chose.