Consider adding a drag & drop event

[thelink2012]

GLFW as of 3.1 provides a callback to queue dropped files and afaik SDL2 also has such event.

[mitchmindtree]

Just an update: It looks like this event has been added, but is only implemented for the win32 api so far.

[mitchmindtree]

I've been looking into how to get this working for cocoa.

In order to receive drag events, cocoa requires implementing the NSDraggingDestination protocol. It seems this involves subclassing NSWindow and then implementing the performDragOperation method which gets called when a drag is released over the window. We could use this callback to add an event to the VecDeque of pending_events. I found a simple example of implementing the NSDraggingDestination protocol in obj c here.

Once implemented, we will have to register the window as a dragging destination for the specific types of files that we can want to handle (in our case, all of them). To do this, we have to call the registerForDraggedTypes method on our window after we have created it and ensured that it is non_nil. This will probably look something like this:

// Register the window as a dragging destination for creating `DroppedFile` events.
msg_send![*window, registerForDraggedTypes:NSArray::arrayWithObject(nil, appkit::NSFilenamesPboardType)];

[mitchmindtree]

The cocoa API supports handling multiple dropped files at once. When this occurs, we could either:

• emit multiple DroppedFile events or
• change DroppedFile(PathBuf) to DroppedFile(Vec<PathBuf>)

The second option might be useful for applications that need to know when multiple files are dropped at once though would be a breaking change. The first option is probably simplest to implement in the meantime.

[thelink2012]

As a side note, Win32 also supports the event of many files at once (and that's what's used in my impl), however I still opted for triggering many events, seems less intrusive imo.

[retep998]

It is possible to support more advanced drag and drop, where the window receives notification of the thing being dragged onto it before it is dropped. This allows for visual feedback to be displayed to the user, such as displaying where the dropped thing will be inserted or whether dropping is allowed.

https://msdn.microsoft.com/en-us/library/windows/desktop/bb776905(v=vs.85).aspx

[retep998]

Also for the record the current Windows implementation only accepts paths that can fit in[u16; winapi::MAX_PATH], which is actually rather small because MAX_PATH is only 255 while in reality paths can be up to 32767 long.

[tomaka]

Closing for rust-windowing/winit#44