From 31945563d89f9d598b8871d88b31bf4d5d7cc434 Mon Sep 17 00:00:00 2001
From: Hajime Hoshi <hajimehoshi@gmail.com>
Date: Thu, 15 Sep 2022 01:30:08 +0900
Subject: [PATCH] internal/atlas: optimize adjustDestinationPixel
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```
go test -bench=BenchmarkAdjustPixel -run=^$ -count=5 ./internal/atlas/
```

```
name           old time/op  new time/op  delta
AdjustPixel-8  2.59ns ± 1%  2.12ns ± 1%  -18.16%  (p=0.008 n=5+5)
```
---
 internal/atlas/image.go      |  7 +++++--
 internal/atlas/image_test.go | 34 ++++++++++++++++++++++++++++++++++
 2 files changed, 39 insertions(+), 2 deletions(-)

diff --git a/internal/atlas/image.go b/internal/atlas/image.go
index bbb314abc..b2dac9270 100644
--- a/internal/atlas/image.go
+++ b/internal/atlas/image.go
@@ -17,7 +17,6 @@ package atlas
 import (
 	"fmt"
 	"image"
-	"math"
 	"runtime"
 	"sync"
 
@@ -805,7 +804,11 @@ func adjustDestinationPixel(x float32) float32 {
 	//     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)))
+	var ix float32
+	ix = float32(int(x))
+	if x < 0 && x != ix {
+		ix -= 1
+	}
 	frac := x - ix
 	switch {
 	case frac < 3.0/16.0:
diff --git a/internal/atlas/image_test.go b/internal/atlas/image_test.go
index 24335a98b..7d6041797 100644
--- a/internal/atlas/image_test.go
+++ b/internal/atlas/image_test.go
@@ -737,6 +737,40 @@ func TestImageWritePixelsModify(t *testing.T) {
 	}
 }
 
+func TestAdjustPixel(t *testing.T) {
+	tests := []struct {
+		X     float32
+		Y     float32
+		Delta float32
+	}{
+		{
+			X:     -0.1,
+			Y:     0.9,
+			Delta: 1,
+		},
+		{
+			X:     -1,
+			Y:     0,
+			Delta: 1,
+		},
+		{
+			X:     -1.9,
+			Y:     1.1,
+			Delta: 3,
+		},
+		{
+			X:     -2,
+			Y:     1,
+			Delta: 3,
+		},
+	}
+	for _, tc := range tests {
+		if rx, ry := atlas.AdjustDestinationPixelForTesting(tc.X)+tc.Delta, atlas.AdjustDestinationPixelForTesting(tc.Y); rx != ry {
+			t.Errorf("adjustDestinationPixel(%f) + 1 must equal to adjustDestinationPixel(%f) but not (%f vs %f)", tc.X, tc.Y, rx, ry)
+		}
+	}
+}
+
 func BenchmarkAdjustPixel(b *testing.B) {
 	for i := 0; i < b.N; i++ {
 		atlas.AdjustDestinationPixelForTesting(float32(i) / 17)