added support for globalCompositeOperation (BlazorExtensions#108)

Author: mizrael

src/Blazor.Extensions.Canvas/Canvas2D/Canvas2DContext.cs

@@ -54,6 +54,7 @@ public class Canvas2DContext : RenderingContext
         private const string RESTORE_METHOD = "restore";
         private const string DRAW_IMAGE_METHOD = "drawImage";
         private const string CREATE_PATTERN_METHOD = "createPattern";
+        private const string GLOBAL_COMPOSITE_OPERATION_PROPERTY = "globalCompositeOperation";
 
         private readonly string[] _repeatNames = new[]
         {
@@ -96,6 +97,8 @@ public class Canvas2DContext : RenderingContext
 
         public float GlobalAlpha { get; private set; } = 1.0f;
 
+        public string GlobalCompositeOperation { get; private set; } = "source-over";
+
         #endregion Properties
 
         public Canvas2DContext(BECanvasComponent reference) : base(reference, CONTEXT_NAME)
@@ -200,6 +203,12 @@ public async Task SetGlobalAlphaAsync(float value)
             await this.BatchCallAsync(GLOBAL_ALPHA_PROPERTY, isMethodCall: false, value);
         }
 
+        public async Task SetGlobalCompositeOperationAsync(string value)
+        {
+            this.GlobalCompositeOperation = value;
+            await this.BatchCallAsync(GLOBAL_COMPOSITE_OPERATION_PROPERTY, isMethodCall: false, value);
+        }
+
         #endregion Property Setters
 
         #region Methods