Add fast-path for SetRGBA/SetNRGBA interfaces, use Set as fallback.

decode.go

@@ -37,6 +37,14 @@ func Decode(hash string, width, height int, punch int) (image.Image, error) {
 	return newImg, nil
 }
 
+type drawImageNRGBA interface {
+	SetNRGBA(x, y int, c color.NRGBA)
+}
+
+type drawImageRGBA interface {
+	SetRGBA(x, y int, c color.RGBA)
+}
+
 // DecodeDraw decodes the given hash into the given image.
 func DecodeDraw(dst draw.Image, hash string, punch float64) error {
 	numX, numY, err := Components(hash)
@@ -85,12 +93,20 @@ func DecodeDraw(dst draw.Image, hash string, punch float64) error {
 				}
 			}
 
-			dst.Set(x, y, color.NRGBA{
-				R: uint8(linearTosRGB(r)),
-				G: uint8(linearTosRGB(g)),
-				B: uint8(linearTosRGB(b)),
-				A: 255,
-			})
+			sR := uint8(linearTosRGB(r))
+			sG := uint8(linearTosRGB(g))
+			sB := uint8(linearTosRGB(b))
+			sA := uint8(255)
+
+			// interface smuggle
+			switch d := dst.(type) {
+			case drawImageNRGBA:
+				d.SetNRGBA(x, y, color.NRGBA{sR, sG, sB, sA})
+			case drawImageRGBA:
+				d.SetRGBA(x, y, color.RGBA{sR, sG, sB, sA})
+			default:
+				d.Set(x, y, color.NRGBA{sR, sG, sB, sA})
+			}
 		}
 	}
 

decode_test.go

@@ -98,3 +98,19 @@ func BenchmarkDecode(b *testing.B) {
 		})
 	}
 }
+
+func BenchmarkDecodeDraw(b *testing.B) {
+	for _, test := range testFixtures {
+		// skip tests without hashes
+		if test.hash == "" {
+			continue
+		}
+
+		b.Run(test.hash, func(b *testing.B) {
+			for i := 0; i < b.N; i++ {
+				dst := image.NewRGBA(image.Rect(0, 0, 32, 32))
+				_ = blurhash.DecodeDraw(dst, test.hash, 1)
+			}
+		})
+	}
+}