Perf' problem when picking child objects on a "crowded" canvas

[LaurentInSeattle]

Context:
I have made a little Jigsaw game using Avalonia, where puzzle pieces are UserControl's (MVVM views) holding a CroppedBitmap and a Clipping path. They are laid at random on a (Pan'able and Zoom'able) Canvas. They all have been given a behaviour implementing Pick, Drag and Move.

Code links for folks who have time to spare:
Game: https://github.com/LaurentInSeattle/Lyt.Jigsaw
Behaviour: https://github.com/LaurentInSeattle/Lyt.Avalonia/blob/main/Lyt.Avalonia.Mvvm/Behaviors/DragMove/DragMovable.cs

Issue:

All is fine as long as the puzzle does not exceed around 250 puzzle pieces (== UserControl's + VM's + Behaviours).
Above performance degrades apparently linearly with piece count.
When going up to close to 1000 pieces, picking a piece lags big time, almost half a second on my "old" machine... :(

Edit:
Not a drawing or layout problem. The delay is about time between clicking the mouse and receiving the PointerPressed event.

Questions:

• Is it "crazy" to have 1000+ objects to pick with Avalonia event handlers?
• I have seen other apps handling more objects than that.. How do "they" do that?
• Any suggestions to improve the issue?

Thanks!

[rabbitism]

you probably need to implement your own canvas. From my guess, it's because every drag move triggers all 1000 elements to re layout which can be expensive.

[LaurentInSeattle]

Nothing drawn or laid out yet. The delay is about time from clicking the mouse until the PointerPressed event is received.

[timunie]

Sounds like a custom rendered control would be better here. Inherit Control and override OnRender.

https://avaloniaui.github.io/Avalonia.Samples/src/Avalonia.Samples/CustomControls/SnowflakesControlSample/

[LaurentInSeattle]

Not a drawing issue: The delay is about time from clicking the mouse until the PointerPressed event is received.

[timunie]

Yep 1000x hit testing. If you set Hittest to false and handle it on your own with a transparent overlay, that should be faster. And here comes drawing on your own in charge, you have all hittest logic in your own hands.

[LaurentInSeattle]

I thought about that but...
How my custom hit test can be made better that the built-in Avalonia one that has been battle tested for 10* years ?
Does it already perform some kind of spatial partitioning to identify the element being hit ?

[LaurentInSeattle]

Issue resolved in Avalonia V12 RC 1