Material Shape for Avalonia

androidx\graphics\graphics-shapes ported to Avalonia.

Features

• Material 3 Expressive Shapes Access the complete set of predefined Material 3 shapes, or customize your own shapes.
• Shape Morphing Create smooth, high-performance animations that morph between any two arbitrary shapes.
• Avalonia Integration:
  • Generate standard Avalonia Geometry objects for custom use.
  • Use MaterialShapeView to render static shapes.
  • Use MorphShapeView to implement morphing animations between two shapes.

Geometry conversion

RoundedPolygon.ToGeometry() and Morph.ToGeometry(progress) mirror androidx's compose/material3/internal/ShapeUtil.kt, including its startAngle, repeatPath and closePath parameters.

Two deviations, both deliberate:

• startAngle defaults to 0 here, not 270. Upstream's toPath is internal and every caller re-centres the result, so its default is harmless there. On a public API a non-zero default would silently rotate — and, since the rotation is about the origin rather than the shape's centre, translate — every shape drawn through it. Pass AvaloniaExtensions.StartAngleTop when porting material3 drawing code.
• The rotation is applied about the origin, exactly as upstream does; the pivot only decides where the first anchor's angle is measured from.

Known limitations

• MorphShapeView builds a fresh StreamGeometry for every Progress change, i.e. once per frame while morphing. This is not an oversight: Avalonia 12's StreamGeometry has no rewind — _strokePath is readonly and re-Open()ing appends — so a geometry cannot be rebuilt in place. Avoiding the per-frame allocation means dropping to a custom draw operation with a reused SKPath, which trades away the non-Skia backends.

Gallery

You can explore the capabilities and play with different Material Shapes by building and running the included Gallery App.