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ScrollViewer and Logical Scroll

ZoomBorder implements ILogicalScrollable so it can participate in Avalonia scrolling infrastructure instead of fighting it.

Why This Matters

Embedding zoomable content inside a ScrollViewer is common, but naive implementations can create feedback loops between viewport transforms and host scroll offsets.

ZoomBorder addresses that through:

  • the ILogicalScrollable implementation in ZoomBorder.ILogicalScrollable.cs
  • CalculateScrollable(...) for computing extent, viewport, and offset from source bounds and the active matrix

Practical Guidance

  • Put a ScrollViewer around the control only when you want scrollbars or host-level scrolling semantics.
  • Review wheel configuration carefully; wheel input may need to pan instead of zoom in some host layouts.
  • Use the existing unit tests around logical scrolling as the baseline behavior contract when modifying this area.
  • Avalonia.Controls.PanAndZoom.ZoomBorder.CalculateScrollable(Avalonia.Rect,Avalonia.Size,Avalonia.Media.Transformation.Matrix,Avalonia.Size@,Avalonia.Size@,Avalonia.Vector@)
  • BringIntoView(...) behavior through the scrollable contract
  • Bounds, Wheel, and Resize