[Feature] Add FillRule property for Polyline/Polygon

[jsuarezruiz]

What does the pull request do?

Adds FillRule support to Polyline/Polygon. Polyline now builds a filled geometry when a Fill is provided and propagates FillRule; PolylineGeometry accepts and applies the fill rule. Samples were updated to demonstrate EvenOdd vs NonZero.

FillRule determines how the intersecting areas contained in a Polyline/Polygon/Geometry are combined.

What is the current behavior?

Polyline and Polygon FillRule had no effect.

What is the updated/expected behavior with this PR?

Polyline and Polygon respect FillRule (EvenOdd vs NonZero) when a Fill is set; hit-testing remains stroke-only when Fill is null.

How was the solution implemented (if it's not obvious)?

• Polyline constructs PolylineGeometry with isFilled = Fill != null and passes FillRule via constructor.
• PolylineGeometry accepts a fill rule and applies it to the stream context.

Checklist

• Added unit tests (if possible)?
• Added XML documentation to any related classes?
• Consider submitting a PR to https://github.com/AvaloniaUI/avalonia-docs with user documentation

Breaking changes

Polyline still returns PolylineGeometry; it now fills only when Fill is set (so hit-testing stays stroke-only by default).

Obsoletions / Deprecations

None.

Fixed issues

Fixes #20158

[jsuarezruiz]

Note: Tested in the Gallery already but there is not a specific Shapes Page. Should include it?

[jsuarezruiz]

Tested with:

<TextBlock Classes="h3" Margin="0,12,0,4">Path FillRule</TextBlock>
  <TextBlock Text="EvenOdd creates holes for nested figures; NonZero keeps the interior filled when the contours wind in the same direction." />
  <StackPanel Orientation="Horizontal" Spacing="12">
    <StackPanel Spacing="4">
      <TextBlock Text="EvenOdd" />
      <Border Background="White" BorderBrush="Gainsboro" BorderThickness="1" Padding="8" CornerRadius="4">
        <Path Width="140"
              Height="140"
              Stretch="Fill"
              Fill="Orange"
              Stroke="Black"
              StrokeThickness="1"
              Data="F1 M 10,10 L 130,10 130,130 10,130 Z M 50,50 L 90,50 90,90 50,90 Z"/>
      </Border>
    </StackPanel>
    <StackPanel Spacing="4">
      <TextBlock Text="NonZero" />
      <Border Background="White" BorderBrush="Gainsboro" BorderThickness="1" Padding="8" CornerRadius="4">
        <Path Width="140"
              Height="140"
              Stretch="Fill"
              Fill="Orange"
              Stroke="Black"
              StrokeThickness="1"
              Data="F0 M 10,10 L 130,10 130,130 10,130 Z M 50,50 L 90,50 90,90 50,90 Z"/>
      </Border>
    </StackPanel>
  </StackPanel>
  <TextBlock Classes="h3" Margin="0,12,0,4">Polygon/Polyline FillRule</TextBlock>
  <TextBlock Text="Self-intersecting polygons show different winding behavior for EvenOdd and NonZero." />
  <StackPanel Orientation="Horizontal" Spacing="12">
    <StackPanel Spacing="4">
      <TextBlock Text="EvenOdd" />
      <Border Background="White" BorderBrush="Gainsboro" BorderThickness="1" Padding="8" CornerRadius="4">
        <Polygon Width="160"
                 Height="160"
                 Stretch="Fill"
                 Fill="Gold"
                 Stroke="Black"
                 StrokeThickness="1"
                 FillRule="EvenOdd"
                 Points="50,0  21,90  98,35  2,35  79,90" />
      </Border>
    </StackPanel>
    <StackPanel Spacing="4">
      <TextBlock Text="NonZero" />
      <Border Background="White" BorderBrush="Gainsboro" BorderThickness="1" Padding="8" CornerRadius="4">
        <Polygon Width="160"
                 Height="160"
                 Stretch="Fill"
                 Fill="Gold"
                 Stroke="Black"
                 StrokeThickness="1"
                 FillRule="NonZero"
                 Points="50,0  21,90  98,35  2,35  79,90" />
      </Border>
    </StackPanel>
  </StackPanel>
  <TextBlock Classes="h3" Margin="0,12,0,4">Polyline FillRule</TextBlock>
  <TextBlock Text="A jagged filled polyline using NonZero/EvenOdd winding (adapted from WPF FillRule sample)." />
  <StackPanel Orientation="Horizontal" Spacing="12">
    <StackPanel Spacing="4">
      <TextBlock Text="EvenOdd" />
      <Border Background="White" BorderBrush="Gainsboro" BorderThickness="1" Padding="8" CornerRadius="4">
        <Polyline Width="200"
                  Height="140"
                  Stretch="Fill"
                  Fill="Red"
                  Stroke="Black"
                  StrokeThickness="2"
                  FillRule="EvenOdd"
                  Points="10,140
                  60,20
                  110,140
                  20,60
                  180,60
                  90,140
                  140,20
                  10,140" />
      </Border>
    </StackPanel>
    <StackPanel Spacing="4">
      <TextBlock Text="NonZero" />
      <Border Background="White" BorderBrush="Gainsboro" BorderThickness="1" Padding="8" CornerRadius="4">
        <Polyline Width="200"
                  Height="140"
                  Stretch="Fill"
                  Fill="Red"
                  Stroke="Black"
                  StrokeThickness="2"
                  FillRule="NonZero"
                  Points="10,140
                  60,20
                  110,140
                  20,60
                  180,60
                  90,140
                  140,20
                  10,140" />
      </Border>
    </StackPanel>
  </StackPanel>

[avaloniaui-bot]

You can test this PR using the following package version. 12.0.999-cibuild0060421-alpha. (feed url: https://nuget-feed-all.avaloniaui.net/v3/index.json) [PRBUILDID]

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[MrJul]

Notes from the API review meeting:

Add a new overload PolylineGeometry(IEnumerable<Point> points, bool isFilled, FillRule fillRule) instead of adding an optional parameter to the existing constructor, which is a binary breaking change.

Also, please add a couple of render tests.

[jsuarezruiz]

Notes from the API review meeting:

Add a new overload PolylineGeometry(IEnumerable<Point> points, bool isFilled, FillRule fillRule) instead of adding an optional parameter to the existing constructor, which is a binary breaking change.

Also, please add a couple of render tests.

Applied changes:

• Restored binary compatibility for PolylineGeometry by reintroducing the original two-parameter constructor and adding a separate three-parameter overload.
• Added render tests.

[MrJul]

There's a conflict on Avalonia.nupkg.xml. Not sure why there are so many changes there! You should be able to completely revert this file since the API break has been reverted.

[MrJul]

LGTM!