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Custom Bounds, Resize, and Rotation

If the built-in behavior is close but not exact, ZoomBorder exposes virtual hooks for custom policy.

Extensibility Points

• GetContentBounds(): return the effective content bounds used for custom constraints
• ValidateTransform(Matrix newMatrix): veto proposed transforms
• OnResized(Size oldSize, Size newSize): apply custom resize policy

Example:

public class CustomZoomBorder : ZoomBorder
{
    protected override Rect GetContentBounds() => base.GetContentBounds();

    protected override bool ValidateTransform(Matrix newMatrix)
    {
        return base.ValidateTransform(newMatrix);
    }

    protected override void OnResized(Size oldSize, Size newSize)
    {
        base.OnResized(oldSize, newSize);
    }
}

When To Override

• content bounds depend on domain data rather than only the child's measured bounds
• certain zoom or pan regions must be blocked
• resize behavior needs to preserve a custom anchor or workflow-specific invariant

Rotation Considerations

Rotation state is configurable, but advanced rotation-heavy surfaces should validate how rotation interacts with bounds, serialization, and any custom overlay math before relying on it as a full scene-graph feature.