Merge pull request #6133 from Splitwirez/arc-shape

Add Arc shape control 2: Electric Boogaloo

src/Avalonia.Controls/Shapes/Arc.cs

@@ -0,0 +1,103 @@
+using System;
+using Avalonia.Media;
+
+namespace Avalonia.Controls.Shapes
+{
+    public class Arc : Shape
+    {
+        /// <summary>
+        /// Defines the <see cref="StartAngle"/> property.
+        /// </summary>
+        public static readonly StyledProperty<double> StartAngleProperty =
+            AvaloniaProperty.Register<Arc, double>(nameof(StartAngle), 0.0);
+
+        /// <summary>
+        /// Defines the <see cref="SweepAngle"/> property.
+        /// </summary>
+        public static readonly StyledProperty<double> SweepAngleProperty =
+            AvaloniaProperty.Register<Arc, double>(nameof(SweepAngle), 0.0);
+
+        static Arc()
+        {
+            StrokeThicknessProperty.OverrideDefaultValue<Arc>(1);
+            AffectsGeometry<Arc>(BoundsProperty, StrokeThicknessProperty, StartAngleProperty, SweepAngleProperty);
+        }
+
+        /// <summary>
+        /// Gets or sets the angle at which the arc starts, in degrees.
+        /// </summary>
+        public double StartAngle
+        {
+            get => GetValue(StartAngleProperty);
+            set => SetValue(StartAngleProperty, value);
+        }
+
+        /// <summary>
+        /// Gets or sets the angle, in degrees, added to the <see cref="StartAngle"/> defining where the arc ends.
+        /// A positive value is clockwise, negative is counter-clockwise.
+        /// </summary>
+        public double SweepAngle
+        {
+            get => GetValue(SweepAngleProperty);
+            set => SetValue(SweepAngleProperty, value);
+        }
+
+        protected override Geometry CreateDefiningGeometry()
+        {
+            var angle1 = DegreesToRad(StartAngle);
+            var angle2 = angle1 + DegreesToRad(SweepAngle);
+
+            var startAngle = Math.Min(angle1, angle2);
+            var sweepAngle = Math.Max(angle1, angle2);
+
+            var normStart = RadToNormRad(startAngle);
+            var normEnd = RadToNormRad(sweepAngle);
+
+            var rect = new Rect(Bounds.Size);
+
+            if ((normStart == normEnd) && (startAngle != sweepAngle)) // Complete ring.
+            {
+                return new EllipseGeometry(rect.Deflate(StrokeThickness / 2));
+            }
+            else if (SweepAngle == 0)
+            {
+                return new StreamGeometry();
+            }
+            else // Partial arc.
+            {
+                var deflatedRect = rect.Deflate(StrokeThickness / 2);
+
+                var centerX = rect.Center.X;
+                var centerY = rect.Center.Y;
+
+                var radiusX = deflatedRect.Width / 2;
+                var radiusY = deflatedRect.Height / 2;
+
+                var angleGap = RadToNormRad(sweepAngle - startAngle);
+
+                var startPoint = GetRingPoint(radiusX, radiusY, centerX, centerY, startAngle);
+                var endPoint = GetRingPoint(radiusX, radiusY, centerX, centerY, sweepAngle);
+
+                var arcGeometry = new StreamGeometry();
+
+                using (var ctx = arcGeometry.Open())
+                {
+                    ctx.BeginFigure(startPoint, false);
+                    ctx.ArcTo(endPoint, new Size(radiusX, radiusY), angleGap, angleGap >= Math.PI,
+                        SweepDirection.Clockwise);
+                    ctx.EndFigure(false);
+                }
+
+                return arcGeometry;
+            }
+        }
+
+        static double DegreesToRad(double inAngle) =>
+            inAngle * Math.PI / 180;
+
+        static double RadToNormRad(double inAngle) => ((inAngle % (Math.PI * 2)) + (Math.PI * 2)) % (Math.PI * 2);
+
+        static Point GetRingPoint(double radiusX, double radiusY, double centerX, double centerY, double angle) =>
+            new Point((radiusX * Math.Cos(angle)) + centerX, (radiusY * Math.Sin(angle)) + centerY);
+    }
+}