Creating a custom fill brush in XAML

Question

How do I create the following shape in XAML?

<Ellipse Height="100" Width="100">
    <Ellipse.Fill>
       ???
    </Ellipse.Fill>
</Ellipse>

LinearGradientBrush can't be transformed in this way? RadialGradientBrush is not suitable either.

Any ideas?

Answer 1

Your best bet would be to create a DrawingBrush with some custom drawing instructions, perhaps divide the ellipse into quarters and fill each with a different RadialGradientBrush.

Answer 2

You can't do it with an ellipse and the built in brushes, but it isn't difficult to write such a shape yourself.

You can draw a lot of "pie slice" shapes and apply a different linear gradient brush to each slice.

This will get you started:

class GradiantEllipse : FrameworkElement
{
    private const double N = 100;

    protected override void OnRender(System.Windows.Media.DrawingContext drawingContext)
    {
        var radius = Math.Min(ActualWidth/2,ActualHeight/2);
        var center = new Point(ActualWidth/2,ActualHeight/2);
        for (int i = 0; i < N; ++i)
        {
            var startAngle = (Math.PI*2/N)*i;
            var endAngle = (Math.PI*2/N)*(i+1)+2*(Math.PI/radius)+1/(2*Math.PI+radius); // + 1px to avoid gap
            var start = new Point(Math.Cos(startAngle)*radius+center.X,
                Math.Sin(startAngle)*radius+center.Y);
            var end = new Point(Math.Cos(endAngle)*radius+center.X,
                Math.Sin(endAngle)*radius+center.Y);
            var figure = new PathFigure();
            figure.StartPoint = center;
            figure.Segments.Add(new LineSegment(start,false));
            figure.Segments.Add(new LineSegment(end,false));
            figure.IsClosed = true;
            var geo = new PathGeometry();
            geo.Figures.Add(figure);

            var gradiant = new LinearGradientBrush(
                Color.FromArgb(255, (byte)((255.0 / N) * i), (byte)((255.0 / N) * i), (byte)((255.0 / N) * i)),
                Color.FromArgb(255, (byte)((255.0 / N) * (i + 1)), (byte)((255.0 / N) * (i + 1)), (byte)((255.0 / N) * (i + 1))),
                Math.Atan2(end.Y - start.Y, end.X - start.X) * 180 / Math.PI);

            drawingContext.DrawGeometry(gradiant, null, geo);
        }
    }
}