Include square line cap in bounds; update WebGPU tests

Author: JimBobSquarePants

src/ImageSharp.Drawing/Processing/Backends/FlushScene.cs

@@ -948,12 +948,18 @@ private static bool TryResolveRasterization(
     private static RectangleF GetStrokeBounds(RectangleF bounds, Pen pen)
     {
         float halfWidth = pen.StrokeWidth * 0.5F;
-        float inflate = pen.StrokeOptions.LineJoin switch
+        float joinInflate = pen.StrokeOptions.LineJoin switch
         {
             LineJoin.Miter or LineJoin.MiterRevert or LineJoin.MiterRound => (float)(halfWidth * Math.Max(pen.StrokeOptions.MiterLimit, 1D)),
             _ => halfWidth
         };
 
+        float capInflate = pen.StrokeOptions.LineCap == LineCap.Square
+            ? halfWidth * MathF.Sqrt(2F)
+            : halfWidth;
+
+        float inflate = MathF.Max(joinInflate, capInflate);
+
         bounds.Inflate(new SizeF(inflate, inflate));
         return bounds;
     }

tests/ImageSharp.Drawing.Tests/Processing/Backends/WebGPUDrawingBackendTests.cs

@@ -934,6 +934,8 @@ public void DrawPath_Stroke_LineJoin_MatchesDefaultOutput<TPixel>(TestImageProvi
         });
 
         void DrawAction(DrawingCanvas<TPixel> canvas) => canvas.Draw(pen, path);
+        IPath outline = path.GenerateOutline(pen.StrokeWidth, pen.StrokeOptions);
+        void DrawReference(DrawingCanvas<TPixel> canvas) => canvas.Fill(pen.StrokeFill, outline);
 
         using Image<TPixel> defaultImage = provider.GetImage();
         RenderWithDefaultBackend(defaultImage, drawingOptions, DrawAction);
@@ -948,14 +950,34 @@ public void DrawPath_Stroke_LineJoin_MatchesDefaultOutput<TPixel>(TestImageProvi
             DrawAction,
             nativeSurfaceInitialImage);
 
-        DebugSaveBackendPair(provider, $"DrawPath_Stroke_LineJoin_{lineJoin}", defaultImage, nativeSurfaceImage);
         AssertBackendPairSimilarity(defaultImage, nativeSurfaceImage, 0.01F);
+
+        using Image<TPixel> referenceImage = provider.GetImage();
+        RenderWithDefaultBackend(referenceImage, drawingOptions, DrawReference);
+
+        using Image<TPixel> defaultComparisonImage = CreateJoinComparisonImage(referenceImage, defaultImage);
+        using Image<TPixel> nativeSurfaceComparisonImage = CreateJoinComparisonImage(referenceImage, nativeSurfaceImage);
+
+        DebugSaveBackendPair(
+            provider,
+            $"DrawPath_Stroke_LineJoin_{lineJoin}",
+            defaultComparisonImage,
+            nativeSurfaceComparisonImage);
         AssertBackendPairReferenceOutputs(
             provider,
             $"DrawPath_Stroke_LineJoin_{lineJoin}",
-            defaultImage,
-            nativeSurfaceImage);
+            defaultComparisonImage,
+            nativeSurfaceComparisonImage);
         AssertGpuPathWhenRequired(nativeSurfaceBackend);
+
+        static Image<TPixel> CreateJoinComparisonImage(Image<TPixel> reference, Image<TPixel> rendered)
+        {
+            Image<TPixel> comparison = new(reference.Width, reference.Height * 2, Color.White.ToPixel<TPixel>());
+            comparison.Mutate(ctx => ctx
+                .DrawImage(reference, new Point(0, 0), 1F)
+                .DrawImage(rendered, new Point(0, reference.Height), 1F));
+            return comparison;
+        }
     }
 
     [WebGPUTheory]
@@ -982,6 +1004,8 @@ public void DrawPath_Stroke_LineCap_MatchesDefaultOutput<TPixel>(TestImageProvid
         });
 
         void DrawAction(DrawingCanvas<TPixel> canvas) => canvas.Draw(pen, path);
+        IPath outline = path.GenerateOutline(pen.StrokeWidth, pen.StrokeOptions);
+        void DrawReference(DrawingCanvas<TPixel> canvas) => canvas.Fill(pen.StrokeFill, outline);
 
         using Image<TPixel> defaultImage = provider.GetImage();
         RenderWithDefaultBackend(defaultImage, drawingOptions, DrawAction);
@@ -996,14 +1020,34 @@ public void DrawPath_Stroke_LineCap_MatchesDefaultOutput<TPixel>(TestImageProvid
             DrawAction,
             nativeSurfaceInitialImage);
 
-        DebugSaveBackendPair(provider, $"DrawPath_Stroke_LineCap_{lineCap}", defaultImage, nativeSurfaceImage);
         AssertBackendPairSimilarity(defaultImage, nativeSurfaceImage, 0.0103F);
+
+        using Image<TPixel> referenceImage = provider.GetImage();
+        RenderWithDefaultBackend(referenceImage, drawingOptions, DrawReference);
+
+        using Image<TPixel> defaultComparisonImage = CreateLineCapComparisonImage(referenceImage, defaultImage);
+        using Image<TPixel> nativeSurfaceComparisonImage = CreateLineCapComparisonImage(referenceImage, nativeSurfaceImage);
+
+        DebugSaveBackendPair(
+            provider,
+            $"DrawPath_Stroke_LineCap_{lineCap}",
+            defaultComparisonImage,
+            nativeSurfaceComparisonImage);
         AssertBackendPairReferenceOutputs(
             provider,
             $"DrawPath_Stroke_LineCap_{lineCap}",
-            defaultImage,
-            nativeSurfaceImage);
+            defaultComparisonImage,
+            nativeSurfaceComparisonImage);
         AssertGpuPathWhenRequired(nativeSurfaceBackend);
+
+        static Image<TPixel> CreateLineCapComparisonImage(Image<TPixel> reference, Image<TPixel> rendered)
+        {
+            Image<TPixel> comparison = new(reference.Width, reference.Height * 2, Color.White.ToPixel<TPixel>());
+            comparison.Mutate(ctx => ctx
+                .DrawImage(reference, new Point(0, 0), 1F)
+                .DrawImage(rendered, new Point(0, reference.Height), 1F));
+            return comparison;
+        }
     }
 
     [WebGPUTheory]
@@ -1240,7 +1284,7 @@ static void AssertBackend(WebGPUDrawingBackend backend)
 
         DebugSaveBackendPair(provider, "SaveLayer_ClipReduce", defaultImage, nativeSurfaceImage);
         AssertBackendPairSimilarity(defaultImage, nativeSurfaceImage, 1F);
-        AssertBackendPairReferenceOutputs(provider, "SaveLayer_ClipReduce", defaultImage, nativeSurfaceImage);
+        AssertBackendPairReferenceOutputs(provider, "SaveLayer_ClipReduce", defaultImage, nativeSurfaceImage, 0.0006F);
         AssertGpuPathWhenRequired(nativeSurfaceBackend);
     }