When dragging and dropping a file on to the Launcher, the Launcher icons that are valid drop receptacles don't highlight until the cursor is over the launcher.

[John Lea]

Update - Implementation test results.

This now works for long sustained drags of files, but for some reason is not consistently triggered by short sharp drags using a trackpad. To reproduce this issue:

1. Make sure Firefox is in the Launcher, and Nautilus is open on a folder containing a .png file

2. 'Left click hold' on the .png file and drag it in a sharp 'drag and stop' action using the trackpad.

Result: the launcher is unaffected 80% of the time. I am assuming this issue is caused is because there is a issue detecting short sharp d&d movements.

The desired resolution would be for the detection of a d&d and the corresponding change in Launcher state to be more rapid, so that drag actions that start and stop inside a timespan of roughly 50ms (or more) are detected.

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As soon as the user starts dragging a file, the Launcher icons that are valid drop receptacles should instantly become highlighted. Icons that are not valid drop receptacles should disappear so that only app icons that are valid drop receptacles are shown.

This needs to happen the instant a user starts dragging a file, regardless of the position of the file on the desktop.

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This bug would be an ideal bug for someone to get started hacking on Unity, here's some information:

 * Time to fix: 10h
 * Difficulty: normal
 * Implementation:

Implementation of this feature is evil due to the nature of XDND.

Short version: When a dnd situation is detected, quickly pop up a new X window (using a nux BaseWindow is the simplest method), collect the required DND information for the launcher to make a descision, then pop down the window as quickly as possible.

Long version:

Create a new BaseWindow type class used purely to collect DND information, called DNDCollectionWindow. It will probably have the following methods.

DNDCollectionWindow::DNDCollectionWindow ()
void DNDCollectionWindow::Collect ()
std::list<char *> DNDCollectionWindow::GetUriList ()

and a signal

DNDCollectionWindow::collected

The window should pop down as fast as possible (but still retain the data). Collection will look specifically for a text/uri-list, as that is the only data relevant to the launcher, and retrieve that data directly for processing by the launcher. If no text/uri-list is available, the collected signal will still fire, but GetUriList should return an empty list.

Once the data is retrieved, it can be used by the launcher to shade launcher icons even before the hover starts. It is important to note that even though the launcher already has the data, it should collect the data a second time as the drag enters the launchers own XWindow. This is to ensure the data has not changed in the mean time (it is allowed to under the XDND specification).

 * Where to look: src/Launcher.cpp
 * Workflow information: http://unity.ubuntu.com/getinvolved/

[David Barth (dbarth)]

Related to https://bugs.launchpad.net/ayatana-design/+bug/723882

[John Lea (johnlea)]

Related to https://bugs.launchpad.net/ayatana-design/+bug/727902

[Didier Roche-Tolomelli (didrocks)]

I can't do that one without breaking the compability between nux and unity, which is forbidden at this state of the cycle as well as being dangerous. Setting in the backlog basket.

Technical reason:
void
Launcher::ProcessDndMove (int x, int y, std::list<char *> mimes)
this function is signaled by Nux, and the mimetypes of the dragged element are only available there. We would need to set the mimetype before, which is an ABI and API break in Nux.

[Didier Roche-Tolomelli (didrocks)]

For further reference: OnUpdateDragManagerTimeout is the destination when most of the code for dnd should be set in case of positive dnd, all but the mimetypes is available there. See http://bazaar.launchpad.net/~didrocks/unity/dnd-with-initial-hilight-poof/revision/1040

[Andrea Azzarone (azzar1)]

I'm locked since nux drag and drop doesn't work at the moment.

[Andrea Azzarone (azzar1)]

@JohnLea: short (or super fast) drag problem should be gone... As soon as possible I make the proposal ;)

[John Lea (johnlea)]

@andyrock

Great, can't wait until it lands ;-)