feat(panel): dnd improvements for the app list

[edfloreshz]

This PR improves the app list drag and drop experience:

• Dragged icon no longer appears three times while dragging
• Icons can now be dragged all the way to the right
• Icon preview is now aligned precisely to the position of the icon in the dock, the cursor's position is used to calculate the exact pickup offset when the drag starts
• Fixed a bug that caused multiple insertions if an icon entered the dock multiple times.

Currently blocked by: pop-os/libcosmic#1161

Current behavior:

2026-03-08.15-13-44.mp4

New behavior:

2026-03-08.15-12-45.mp4

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[edfloreshz]

I've noticed some inconsistencies, please hold on merging this until I fix them.

[jacobgkau]

I've noticed some inconsistencies, please hold on merging this until I fix them.

I've marked as a draft for you. Just let us know when it's ready to look at.

[edfloreshz]

Reworked a few things to address some inconsistencies, also fixed a bug that caused multiple insertions if DndEnter fired repeatedly.

Would appreciate a second pair of eyes before we merge, happy to discuss any of the changes.

[wash2]

I'd like to revisit this after the rebase updates are merged, and fix the libcosmic issue before merging the changes.

[edfloreshz]

@wash2 Yesterday I bumped the applet to the latest libcosmic rev and I noticed some issues with how the app list was rendered, if you'd like I could push a branch for you to test.

[edfloreshz]

@wash2 I bumped libcosmic to the latest rev and I can't replicate the issues I had last time, I think we're good to merge this unless you find any issues.

[wash2]

The code looks fine, but when I tested it with the master branch for the panel, icons weren't drawn. It might be because of a panel bug though and it seems to be fixed when testing with pop-os/cosmic-panel#602 so I think it is fine if it is merged after the panel smithay update.

[jacobgkau]

I have a few concerns with this.

1. Sometimes, the tooltip icon doesn't show up. This was already a bug before, but together with this change, we now end up dragging something that we can't see what it is, since this removes the on-dock previews and leaves only the tooltip (when it works).

2026-05-13.14-44-27.mp4

2. I'm seeing that if I drag an icon out of the dock, it's impossible to drag it back in (even if I haven't released the mouse button yet). This bug also occurred sometimes before, but before, it would result in the icon staying where it was before the drag started. Now, it results in the icon being removed from the dock, which takes more effort to recover from.

2026-05-13.14-43-23.mp4

3. I also had one instance where the dock got stuck showing an app as running when I'd actually already quit it. I'm not sure if this was a regression or not (I haven't made it happen a second time yet, but it might've had something to do with pinning/unpinning the app).

2026-05-13.14-43-58.mp4

We'll want @pop-os/ux input on this kind of change. @pop-os/ux, if the tooltip was working 100% of the time, would it be the desired implementation to have the icon tooltip and a blank gap in the dock where the icon will go when dropped? Or would it be better to have a single dynamic instance of the icon in the dock where the icon's going to be placed, maybe without the tooltip (more similar to how the new DnD implementation in the App Library's going to work)? I guess if we had the icon draggable on the dock itself (like the app library folders), then we might still want the tooltip when the cursor leaves the dock, so the user knows they're still holding onto the icon when it's in the "drop off the dock to remove" state.

[edfloreshz]

Now that you mention it, I also noticed some quirks while running inside the panel, including the inability to drag icons back in, but I can't replicate this while the applet runs standalone, which suggests the issue lies with the panel itself.

I'm not sure if the issue @wash2 mentions could improve this tho.