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Fix flickering in table view

David Edmundson requested to merge work/fix_flickering into master

We have a list of delegates:

Whenever we get a layoutChange signal (from a re-order), table view recycles all of them. Every binding, text and value changes.

Our backgrounds have two rectangles:

One does a white or grey line:
color: (row % 2 == 0) ? Kirigami.Theme.backgroundColor :
Kirigami.Theme.alternateBackgroundColor
One draws the highlight:
	color: Kirigami.Theme.backgroundColor
        Kirigami.Theme.inherit: false
        Kirigami.Theme.colorSet: Kirigami.Theme.Selection
        opacity: selected ? 1: 0

That's all well and good, but we don't want the text to be black on blue, so there's some code here that handles this in the parent item of the cell background.

	Kirigami.Theme.colorSet: background.selected ?
Kirigami.Theme.Selection : Kirigami.Theme.View
	Kirigami.Theme.inherit: false

A noticable quirk there is that our background to draw the white and grey alternating rows actually draws a blue background because it inherits the selected colourSet from our parent Kirigami.Theme. That is marked as being "Selection" not "View"

Why does that cause a problem?

After a reshuffle what happens is:

  • All bindings update, Qt does everything perfectly

  • The colours in the real highlight update on time

  • The colours in the background are delayed because they come from the parent ColorSet

  • Kirigami theme propagation has some "event compression" before propagating to children. IMHO this is a Kirigami bug.

  • The old selected item which is now some random item renders a blue highlight where it should be rendering the white or grey background.

This patch moves logic for the selection colour into rectangle for drawing the main background, whic also means we explicitly set a Kirigami.ColorSet there.

This also helps differentiate highlighted + vs highlighted + mouse over which brings it more in line with the desktop.

BUG: 436803

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