Add small-geometry fast path to rasterizer

JimBobSquarePants · JimBobSquarePants · commit 34f110f76b5d · 2026-03-06T22:31:02.000+10:00
diff --git a/src/ImageSharp.Drawing/Processing/Backends/DefaultRasterizer.cs b/src/ImageSharp.Drawing/Processing/Backends/DefaultRasterizer.cs
@@ -330,10 +330,11 @@ private static bool TryRasterizeParallel(
         }
 
         int tileCount = (height + tileHeight - 1) / tileHeight;
-        if (tileCount == 1)
+        if (tileCount == 1 || edgeCount <= 64)
         {
-            // Tiny workload fast path: avoid bucket construction and worker scheduling
-            // when everything fits in a single tile.
+            // Small-geometry fast path: for paths with few edges (e.g. a stroked line
+            // producing ~6-10 edges), iterating all edges against all rows is far cheaper
+            // than the allocation overhead of band sorting + Parallel.For scheduling.
             RasterizeSingleTileDirect(
                 edgeMemory.Span[..edgeCount],
                 width,

Original file line number	Diff line number	Diff line change
`@@ -330,10 +330,11 @@ private static bool TryRasterizeParallel(`
`330`	`330`	`}`
`331`	`331`
`332`	`332`	`int tileCount = (height + tileHeight - 1) / tileHeight;`
`333`		`- if (tileCount == 1)`
	`333`	`+ if (tileCount == 1 \|\| edgeCount <= 64)`
`334`	`334`	`{`
`335`		`- // Tiny workload fast path: avoid bucket construction and worker scheduling`
`336`		`- // when everything fits in a single tile.`
	`335`	`+ // Small-geometry fast path: for paths with few edges (e.g. a stroked line`
	`336`	`+ // producing ~6-10 edges), iterating all edges against all rows is far cheaper`
	`337`	`+ // than the allocation overhead of band sorting + Parallel.For scheduling.`
`337`	`338`	`RasterizeSingleTileDirect(`
`338`	`339`	`edgeMemory.Span[..edgeCount],`
`339`	`340`	`width,`