Add ability to drag files to and from external applications

[AW1534]

Adds the ability to drag files in and out of LMMS. This required a bit more refactoring than I expected.

video2.mp4

I should note that this doesn't just work to and from the desktop, I've tested with firefox, CLion, dolphin and discord. It also works with more than just sample files (projects, presets, midis, vsts)

[AW1534]

To hell with CodeFactor.

[AW1534]

once #7627 is merged, I'd like to add the ability to drag sample clips out of LMMS too. That could be for a different PR though.

[regulus79]

I tested this briefly, and it seems to work! I'm using nautilus on GNOME to drag files in.

Things I noticed (these aren't that important though):

• Dragging in .xml files which are not presets causes a dummy instrument(?) to be added, and when you click on it, LMMS crashes. This is sort of also in master, but it gives you a warning first.
• You can't drag in .sf2 files (I think this is in master too)
• You can't drag in vst effects into an effect chain

[AW1534]

Dragging in .xml files which are not presets causes a dummy instrument(?) to be added, and when you click on it, LMMS crashes. This is sort of also in master, but it gives you a warning first.

Okay, this should be a relatively simple fix.

You can't drag in .sf2 files (I think this is in master too)

Thats actually not in master, it's is a regression- Nice catch!

You can't drag in vst effects into an effect chain

This is out of scope as it isn't in master, but it's definitely a good idea for another PR.

[regulus79]

I tested this again, and those two issues do appear to be fixed!

[headquarter8302]

In Windows MSVC, dragging instruments to the Song-Editor doesn't work
Edit: I used the right-click menu to insert Mallets, OBS didn't capture the context menu

2025-04-18.23-03-41.mp4