Adding new funcs. Related to #2 (2)

README.md

@@ -27,7 +27,7 @@ Release note (v4): simplified func `Icon`; more than 2x reduction of icon memory
 
 `DefaultThresholds` prints default thresholds used in func `Similar` and `Similar90270`, as a starting point for selecting thresholds on `EucMetric` and `PropMetric`.
 
-`Rotate90` and `Rotate270` turn an icon +90° or -90° clockwise. Those are useful if you test for custom similarity with `EucMetric` and `PropMetric` for rotated images. Or if you also decide to compare to images rotated +180° (by applying `Rotate90` twice).
+`Rotate90` turns an icon 90° clockwise. This is useful for developing custom similarity function for rotated images with `EucMetric` and `PropMetric`. Or if you also decide to compare to images rotated +180° (by applying `Rotate90` twice).
 
 [Go doc](https://pkg.go.dev/github.com/vitali-fedulov/images4) for code reference.
 

icon.go

@@ -252,22 +252,3 @@ func Rotate90(icon IconT) IconT {
 
 	return rotated
 }
-
-// Rotate rotates an icon by 270 degrees clockwise.
-func Rotate270(icon IconT) IconT {
-
-	var c1, c2, c3 float64
-	rotated := sizedIcon(IconSize)
-	for x := 0; x < IconSize; x++ {
-		for y := 0; y < IconSize; y++ {
-			c1, c2, c3 = Get(icon, IconSize, image.Point{x, y})
-			Set(rotated, IconSize, image.Point{y, IconSize - 1 - x},
-				c1, c2, c3)
-		}
-	}
-
-	// Swap image sizes.
-	rotated.ImgSize.X, rotated.ImgSize.Y = icon.ImgSize.Y, icon.ImgSize.X
-
-	return rotated
-}

icon_test.go

@@ -168,13 +168,4 @@ func TestRotate(t *testing.T) {
 		t.Errorf("Rotate(icon0) is not similar to icon90")
 		return
 	}
-
-	img270, _ := Open(path.Join("testdata", "rotate", "270.jpg"))
-	icon270 := Icon(img270)
-
-	if !Similar(Rotate270(icon0), icon270) {
-		t.Errorf("Rotate(icon0) is not similar to icon270")
-		return
-	}
-
 }

similarity.go

@@ -107,11 +107,13 @@ func Similar90270(iconA, iconB IconT) bool {
 		return true
 	}
 
+	// iconB rotated 90 degrees.
 	if Similar(iconA, Rotate90(iconB)) {
 		return true
 	}
 
-	if Similar(iconA, Rotate270(iconB)) {
+	// As if iconB was rotated 270 degrees.
+	if Similar(Rotate90(iconA), iconB) {
 		return true
 	}