712184 - Setting a panel as the dragImage with a mouse cursor located inside of the panel breaks drag events on the browser UI

Status: RESOLVED FIXED

(Core :: XUL, defect)

Description

[Jared Wein [:jaws] (please needinfo? me)]

Attachment: Small patch that reproduces the behavior

Using the following markup:

> <xul:panel type="drag" allowevents="false" style="pointer-events: none;"><xul:label value="Hello, world!" /></xul:panel>

If I call |event.dataTransfer.setDragImage(panel, 5, 5)|, I am unable to get any drag events on top of the the browser chrome. However, if I change the cursor coordinates {-1, -1}, then the drag events work as expected.

I have attached a patch that reproduces this behavior. To repro, apply the patch, build /browser/base && /browser/themes, then try dragging the bookmark star to the bookmarks toolbar. If the cursor coordinates are changed to {-1, -1}, then the drag item will correctly be dragged to the bookmarks toolbar.

Comment 1

[Frank Yan (:fryn)]

Neil, this is the drag panel problem that I brought up when attempting to implement tab animations.

Comment 2

[Neil Deakin]

Does it work if you set noautohide="true" ?

If so, then we may just need to adjust nsXULPopupManager::GetVisiblePopups to check IsDragPopup in both loops.

Comment 3

[Jared Wein [:jaws] (please needinfo? me)]

(In reply to Neil Deakin from comment #2)
> Does it work if you set noautohide="true" ?

Unfornately not. I set noautohide="true" on the panel and changed the call to setDragImage to use the coordinates of {10, 10}, but the cursor is now the "not-allowed" style while dragging the panel.

Comment 4

[Jared Wein [:jaws] (please needinfo? me)]

Neil, do you think you could help greatwarrior here with fixing this bug?

Comment 5

[Amod [:AMoz]]

thank you for allowing me to work on this bug. But I am not clear with what exactly the bug is about. Can anyone explain it to me in detail ?
Thanks !

Comment 6

[Neil Deakin]

Attachment: Testcase

This is a testcase that shows the behaviour. Dragging the popup should highlight the red boxes in blue when hovering over them.

The bug is that the mouse events are getting sent to blocked to/by the drag feedback image.

Changing the arguments to setDragImage to -20, -20 makes it work as this causes the drag feedback image to be offset from the mouse cursor.

I can help but note that this isn't a simple bug and requires digging into platform specific event handling code.

Comment 7

[Amod [:AMoz]]

I would prefer to keep the assignee to default until i make some significant contribution... I am currently studying the test case. Actually I am not well-versed with XUL.

Comment 8

[Neil Deakin]

This should have been fixed by 943759:

Use:
 <panel type="drag" mousethrough="always"/>