Drag'n'drop in R3GUI

Back to using this blog (before I move somewhere else again)!
Let's start with something simple: @GrahamChiu was interested to see how to do drag'n'drop in R3GUI. Here is it:

Some explanation

DRAGGER is style used for dragging. It's simple box, but you can use anything you want.

Dragger / on-click

You need to define ON-CLICK actor to catch MOUSE-DOWN event:

on-click: [
    if arg/type = 'down [
        return init-drag face arg/offset
    ]
]

This will initialize and return the dragging object.

Dragger / on-drag

You also need to add ON-DRAG actor to process movement:

on-drag: [
    face/gob/offset: arg/offset - arg/base
    show face/gob
]

Argument for this actor is the drag object defined in ON-CLICK actor with INIT-DRAG function. The drag object holds original position and new offset (and also some other fields that are not interesting for this simple tutorial).

Dropper / on-drop

For faces that accept our DRAGGER face we need to implement ON-DROP actor:

on-drop: [
    append-content face arg/face
    return true
]

This actor just adds our DRAGGER face to target panel and returns TRUE to indicate everything went well.

Notes

If you drop the DRAGGER on face that has no ON-DROP defined, DRAGGER will return to original position automatically.

Conclusion

As you can see, it's fairly easy. Feel free to ask about details!