Optimize binary size and thumbnail performance

thumb_image_test.go

@@ -0,0 +1,56 @@
+package main
+
+import (
+	"bytes"
+	"image"
+	"image/jpeg"
+	"testing"
+)
+
+// testPhoto returns a JPEG-decoded (so *image.YCbCr, 4:2:0) image with an odd
+// size and a non-zero origin to exercise the plane offset arithmetic.
+func testPhoto(t testing.TB, w, h int) *image.YCbCr {
+	t.Helper()
+	src := image.NewRGBA(image.Rect(0, 0, w, h))
+	for i := range src.Pix {
+		src.Pix[i] = uint8(i*7 + i/w)
+	}
+	var buf bytes.Buffer
+	if err := jpeg.Encode(&buf, src, &jpeg.Options{Quality: 90}); err != nil {
+		t.Fatal(err)
+	}
+	img, err := jpeg.Decode(&buf)
+	if err != nil {
+		t.Fatal(err)
+	}
+	return img.(*image.YCbCr).SubImage(image.Rect(3, 5, w, h)).(*image.YCbCr)
+}
+
+func TestResizeBoxYCbCrMatchesGeneric(t *testing.T) {
+	src := testPhoto(t, 1001, 667)
+	fast := resizeBox(src, 120).(*image.RGBA)
+	// Hide the concrete type so resizeBox takes the generic At() path.
+	slow := resizeBox(struct{ image.Image }{src}, 120).(*image.RGBA)
+	if fast.Bounds() != slow.Bounds() {
+		t.Fatalf("bounds %v != %v", fast.Bounds(), slow.Bounds())
+	}
+	for i := range fast.Pix {
+		if fast.Pix[i] != slow.Pix[i] {
+			t.Fatalf("pixel byte %d: fast %d, generic %d", i, fast.Pix[i], slow.Pix[i])
+		}
+	}
+}
+
+func BenchmarkResizeBox(b *testing.B) {
+	src := testPhoto(b, 4000, 3000)
+	b.Run("ycbcr", func(b *testing.B) {
+		for i := 0; i < b.N; i++ {
+			resizeBox(src, 300)
+		}
+	})
+	b.Run("generic", func(b *testing.B) {
+		for i := 0; i < b.N; i++ {
+			resizeBox(struct{ image.Image }{src}, 300)
+		}
+	})
+}