429959 - Tooltips show at the wrong location under UI scaling

Status: NEW

(Core :: Widget: Cocoa, defect)

Description

[Stuart Morgan]

Tooltips are given to us in Gecko coordinates, and we aren't account for scaling correctly, so they show X times too far down and to the right (where X is the scale factor).

I've found that tooltips and hover effects are unreliable in general under scaling (which would be another, probably core, bug, that I haven't pinned down and filed yet); for testing this issue, I've found that starting a drag of the image works well to force the tooltip to display.

Comment 1

[Stuart Morgan]

Actually, we aren't doing anything wrong; Gecko is giving us the wrong values.
The expectation is that nsITooltipListener::OnShowTooltip would give us Gecko
coordinates (meaning scaled), but instead we get a point that is device pixels
from the upper left corner of the ChildView.

I would guess that it's nsChildView::WidgetToScreen, since that definitely
makes bad assumptions about window/screen vs view coordinates, but since none
of Cocoa Widgets has been audited for this kind of problem it's hard to be
sure.