internal/atlas: add a benchmark for adjustDestinationPixel

internal/atlas/export_test.go

@@ -59,6 +59,5 @@ func (i *Image) EnsureIsolatedForTesting() {
 	i.ensureIsolated()
 }
 
-func ResolveDeferredForTesting() {
+var ResolveDeferredForTesting = resolveDeferred
-	resolveDeferred()
+var AdjustDestinationPixelForTesting = adjustDestinationPixel
-}

internal/atlas/image.go

@@ -799,6 +799,12 @@ func DumpImages(graphicsDriver graphicsdriver.Graphics, dir string) (string, err
 func adjustDestinationPixel(x float32) float32 {
 	// Avoid the center of the pixel, which is problematic (#929, #1171).
 	// Instead, align the vertices with about 1/3 pixels.
+	//
+	// The intention here is roughly this code:
+	//
+	//     float32(math.Floor((float64(x)+1.0/6.0)*3) / 3)
+	//
+	// The actual implementation is more optimized than the above implementation.
 	ix := float32(math.Floor(float64(x)))
 	frac := x - ix
 	switch {

internal/atlas/image_test.go

@@ -737,4 +737,10 @@ func TestImageWritePixelsModify(t *testing.T) {
 	}
 }
 
+func BenchmarkAdjustPixel(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		atlas.AdjustDestinationPixelForTesting(float32(i) / 17)
+	}
+}
+
 // TODO: Add tests to extend image on an atlas out of the main loop