Drag & Drop meta-issue

[Osspial]

This is mostly a stub issue to keep track of progress on improvements to the drag/drop API:

• Dropping lists of files
• Dropping non-file data
  • Dropping multiple types of data at once (i.e. receiving unformatted text and a formatted, HTML version of that text)
  • Potential datatypes to support:
    • Text
    • HTML
    • Image
    • Audio

I did some research into platform-specific clipboard APIs, and as far as I can tell those are the datatypes that we can probably support across all platforms. I'm hesitant to support audio data sine there seems to be way more variance in how platforms support that than the other datatypes, but from what I've seen most platforms expose it in one way or another.

[maroider]

A couple of relevant issues have cropped up since this issue was created:

• The position of the thing being dragged over the window isn't delivered to users (Drag&Drop API / HoveredFile, DroppedFile #1550)
• Drag & Drop isn't implemented on Wayland (Support drag and drop on wayland #1881)

[janus-culsans]

I think out of all these issues #1550 would be the best starting point, also given that it has the most upvotes.
Essentially this boils down to allowing the cursor position to be read while the mouse is dragging something over the window.
This is completely impossible currently.

[kchibisov]

The mouse coordinates are sent during dnd? You clearly know where file is dropped. It's just not attached to the event itself and is sent separately.

[janus-culsans]

Why not just tell how it is sent? 😄
CursorMoved is not getting sent, unless bevy uses some very old version of winit or somehow breaks it.
Do you mean DeviceEvent::MouseMotion?

Ah okay, I think I now get it, Cursor... are WindowEvents, so they're "fixed" to the window. When you drop a file into a window, it is inactive and therefore no cursor events fire, only MouseMotion.
That still means #1550 would be greatly appreciated, but I could hack together my own window-relative coordinates on drag.
Probably something like:

1. save cursor position in a Vec2
2. when dragging a file and entering the window, HoveredFile is sent
3. now start adjusting the saved cursor position based on MouseMotion (and clamp to window size)
4. when window is left while dragging, HoveredFileCancelled is sent / when dragging stops on window, DroppedFile is sent
5. now stop adjusting the saved cursor position

Oh wait, this doesn't make sense, as you would have to enter the window with your cursor at the exact position you left it :)
So instead, you would have to save the exact position of the cursor even while outside of the window.

TLDR; There is no workaround.

[kchibisov]

@janus-culsans The cursor position should be broadcasted during the drag and drop. It could be that a particular platform isn't doing so which could indicate a bug. The events are coming not from the drag and drop events, but from Cursor window events, so maybe on a platforms you're testing it's lacking.

[goolord]

it would be nice to support both drag & drop as a target AND as a source

[janus-culsans]

@kchibisov if the unsupported platform is MSWindows, okay?

[kchibisov]

@janus-culsans are you planning to implement something mentioned here?

[janus-culsans]

@kchibisov I have no knowledge of your internals and no time left, otherwise I would have probably understood your other comments and taken a shot.
I'm sorry, it's just frustrating.

DnD has this weird half-OS half-App-UX problem, which the web standards also could not solve well. Then sometimes you want file DnD, sometimes whiteboardish DnD..
My usecase is also basic drop containers. And I want to show something while hovering over such a container without dropping.