transform: optimize arbitrary angle rotation for multiples of 90 degrees

disintegration · Aug 6, 2017 · a585802 · a585802
1 parent 01751ce
commit a585802
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diff --git a/transform.go b/transform.go
@@ -206,6 +206,19 @@ func Rotate270(img image.Image) *image.NRGBA {
 // The angle parameter is the rotation angle in degrees.
 // The bgColor parameter specifies the color of the uncovered zone after the rotation.
 func Rotate(img image.Image, angle float64, bgColor color.Color) *image.NRGBA {
+	angle = angle - math.Floor(angle/360)*360
+
+	switch angle {
+	case 0:
+		return Clone(img)
+	case 90:
+		return Rotate90(img)
+	case 180:
+		return Rotate180(img)
+	case 270:
+		return Rotate270(img)
+	}
+
 	src := toNRGBA(img)
 	srcW := src.Bounds().Max.X
 	srcH := src.Bounds().Max.Y

diff --git a/transform_test.go b/transform_test.go
@@ -406,6 +406,170 @@ func TestRotate(t *testing.T) {
 				},
 			},
 		},
+		{
+			"Rotate -360*10",
+			&image.NRGBA{
+				Rect:   image.Rect(-1, -1, 0, 1),
+				Stride: 1 * 4,
+				Pix: []uint8{
+					0x00, 0xff, 0x00, 0xff,
+					0xff, 0x00, 0x00, 0xff,
+				},
+			},
+			-360 * 10,
+			color.Black,
+			&image.NRGBA{
+				Rect:   image.Rect(0, 0, 1, 2),
+				Stride: 1 * 4,
+				Pix: []uint8{
+					0x00, 0xff, 0x00, 0xff,
+					0xff, 0x00, 0x00, 0xff,
+				},
+			},
+		},
+		{
+			"Rotate -360*10 + 90",
+			&image.NRGBA{
+				Rect:   image.Rect(-1, -1, 0, 1),
+				Stride: 1 * 4,
+				Pix: []uint8{
+					0xff, 0x00, 0x00, 0xff,
+					0x00, 0xff, 0x00, 0xff,
+				},
+			},
+			-360*10 + 90,
+			color.Black,
+			&image.NRGBA{
+				Rect:   image.Rect(0, 0, 2, 1),
+				Stride: 2 * 4,
+				Pix: []uint8{
+					0xff, 0x00, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff,
+				},
+			},
+		},
+		{
+			"Rotate -360*10 + 180",
+			&image.NRGBA{
+				Rect:   image.Rect(-1, -1, 0, 1),
+				Stride: 1 * 4,
+				Pix: []uint8{
+					0xff, 0x00, 0x00, 0xff,
+					0x00, 0xff, 0x00, 0xff,
+				},
+			},
+			-360*10 + 180,
+			color.Black,
+			&image.NRGBA{
+				Rect:   image.Rect(0, 0, 1, 2),
+				Stride: 1 * 4,
+				Pix: []uint8{
+					0x00, 0xff, 0x00, 0xff,
+					0xff, 0x00, 0x00, 0xff,
+				},
+			},
+		},
+		{
+			"Rotate -360*10 + 270",
+			&image.NRGBA{
+				Rect:   image.Rect(-1, -1, 0, 1),
+				Stride: 1 * 4,
+				Pix: []uint8{
+					0xff, 0x00, 0x00, 0xff,
+					0x00, 0xff, 0x00, 0xff,
+				},
+			},
+			-360*10 + 270,
+			color.Black,
+			&image.NRGBA{
+				Rect:   image.Rect(0, 0, 2, 1),
+				Stride: 2 * 4,
+				Pix: []uint8{
+					0x00, 0xff, 0x00, 0xff, 0xff, 0x00, 0x00, 0xff,
+				},
+			},
+		},
+		{
+			"Rotate 360*10",
+			&image.NRGBA{
+				Rect:   image.Rect(-1, -1, 0, 1),
+				Stride: 1 * 4,
+				Pix: []uint8{
+					0x00, 0xff, 0x00, 0xff,
+					0xff, 0x00, 0x00, 0xff,
+				},
+			},
+			360 * 10,
+			color.Black,
+			&image.NRGBA{
+				Rect:   image.Rect(0, 0, 1, 2),
+				Stride: 1 * 4,
+				Pix: []uint8{
+					0x00, 0xff, 0x00, 0xff,
+					0xff, 0x00, 0x00, 0xff,
+				},
+			},
+		},
+		{
+			"Rotate 360*10 + 90",
+			&image.NRGBA{
+				Rect:   image.Rect(-1, -1, 0, 1),
+				Stride: 1 * 4,
+				Pix: []uint8{
+					0xff, 0x00, 0x00, 0xff,
+					0x00, 0xff, 0x00, 0xff,
+				},
+			},
+			360*10 + 90,
+			color.Black,
+			&image.NRGBA{
+				Rect:   image.Rect(0, 0, 2, 1),
+				Stride: 2 * 4,
+				Pix: []uint8{
+					0xff, 0x00, 0x00, 0xff, 0x00, 0xff, 0x00, 0xff,
+				},
+			},
+		},
+		{
+			"Rotate 360*10 + 180",
+			&image.NRGBA{
+				Rect:   image.Rect(-1, -1, 0, 1),
+				Stride: 1 * 4,
+				Pix: []uint8{
+					0xff, 0x00, 0x00, 0xff,
+					0x00, 0xff, 0x00, 0xff,
+				},
+			},
+			360*10 + 180,
+			color.Black,
+			&image.NRGBA{
+				Rect:   image.Rect(0, 0, 1, 2),
+				Stride: 1 * 4,
+				Pix: []uint8{
+					0x00, 0xff, 0x00, 0xff,
+					0xff, 0x00, 0x00, 0xff,
+				},
+			},
+		},
+		{
+			"Rotate 360*10 + 270",
+			&image.NRGBA{
+				Rect:   image.Rect(-1, -1, 0, 1),
+				Stride: 1 * 4,
+				Pix: []uint8{
+					0xff, 0x00, 0x00, 0xff,
+					0x00, 0xff, 0x00, 0xff,
+				},
+			},
+			360*10 + 270,
+			color.Black,
+			&image.NRGBA{
+				Rect:   image.Rect(0, 0, 2, 1),
+				Stride: 2 * 4,
+				Pix: []uint8{
+					0x00, 0xff, 0x00, 0xff, 0xff, 0x00, 0x00, 0xff,
+				},
+			},
+		},
 	}
 	for _, test := range testCases {
 		got := Rotate(test.src, test.angle, test.bg)