Canvas is not clearing children correctly on current master

[HendrikMennen]

The Canvas takes about 5-10 times longer on current master to update than it did before.
Ram usage is about the same.

It also appears to not remove it's children correctly anymore while calling canvas.children.Clear()

before

0.8.999-cibuild0004086-beta

after

0.8.999-cibuild0004126-beta

[MarchingCube]

Could you provide a small repro case?

[HendrikMennen]

https://github.com/HendrikMennen/CanvasRepro
I know the performance difference is not really noticeable here. Could be because of using DispatcherTimer?

However it shows that there seems to be something wrong with Canvas.Children.Clear(), since the Canvas is not cleared anymore in the second picture

0.8.999-cibuild0004086-beta

0.8.999-cibuild0004126-beta

[ahopper]

the dirty rects don't appear to be correctly updated on removing items.

[ahopper]

removing this line

Avalonia/src/Avalonia.Visuals/Rendering/SceneGraph/VisualNode.cs

Line 216 in 0491a0d

scene.Remove(node);

makes it work (not the solution but a pointer maybe) @grokys

[grokys]

Thanks @ahopper - looks like this was introduced by #3004 then. Will look into it.

[ahopper]

In debugging this the Bounds of the Lines in the repro seemed to have zero height by the time they were added to the dirty rects.

[Gillibald]

When you clear a control's children should that invalidate the region that is covered by the control?

BTW it is not wise to clear a control's children just to add most of its previous children again. Better try work with existing items (object pooling).