PaletteKey option implemented

README.md

@@ -19,6 +19,7 @@ type Options struct {
 	Font        *truetype.Font
 	Palette     []color.Color
 	LetterColor color.Color
+	PaletteKey  string
 }
 ```
 
@@ -34,6 +35,10 @@ img, err := letteravatar.Draw(100, 'A', &letteravatar.Options{
 })
 ```
 
+## Documentation
+
+[https://godoc.org/github.com/disintegration/letteravatar](https://godoc.org/github.com/disintegration/letteravatar)
+
 ## Examples
 
 ![](example/Alice.png)
@@ -103,3 +108,5 @@ func main() {
 The package "letteravatar" is distributed under the terms of the MIT license.
 
 The Roboto-Medium font is distributed under the terms of the Apache License v2.0.
+
+See [LICENSE](LICENSE).

draw.go

@@ -19,6 +19,11 @@ type Options struct {
 	Font        *truetype.Font
 	Palette     []color.Color
 	LetterColor color.Color
+
+	// PaletteKey is used to pick the background color from the Palette.
+	// Using the same PaletteKey leads to the same background color being picked.
+	// If PaletteKey is empty (default) the background color is picked randomly.
+	PaletteKey string
 }
 
 var defaultLetterColor = color.RGBA{0xf0, 0xf0, 0xf0, 0xf0}
@@ -43,7 +48,11 @@ func Draw(size int, letter rune, options *Options) (image.Image, error) {
 
 	var bgColor color.Color = color.RGBA{0x00, 0x00, 0x00, 0xff}
 	if len(palette) > 0 {
-		bgColor = palette[randint(len(palette))]
+		if options != nil && len(options.PaletteKey) > 0 {
+			bgColor = palette[keyindex(len(palette), options.PaletteKey)]
+		} else {
+			bgColor = palette[randint(len(palette))]
+		}
 	}
 
 	return drawAvatar(bgColor, letterColor, font, size, letter)
@@ -100,6 +109,14 @@ func newRGBA(w, h int, c color.Color) *image.RGBA {
 	return img
 }
 
+func keyindex(n int, key string) int {
+	var index int64
+	for _, r := range key {
+		index = (index + int64(r)) % int64(n)
+	}
+	return int(index)
+}
+
 var (
 	rng   = rand.New(rand.NewSource(time.Now().UnixNano()))
 	rngMu = new(sync.Mutex)

draw_test.go

@@ -70,6 +70,33 @@ func TestDraw(t *testing.T) {
 	}
 }
 
+func TestPaletteKey(t *testing.T) {
+	users := []string{
+		"Username 1",
+		"Username 2",
+		"Username 3",
+		"Username 4",
+		"Username 5",
+	}
+	avatars := make(map[string]image.Image)
+	for _, u := range users {
+		img, err := Draw(30, []rune(u)[0], &Options{PaletteKey: u})
+		if err != nil {
+			t.Fatalf("failed to create avatar for %s: %s", u, err)
+		}
+		avatars[u] = img
+	}
+	for _, u := range users {
+		img, err := Draw(30, []rune(u)[0], &Options{PaletteKey: u})
+		if err != nil {
+			t.Fatalf("failed to create avatar for %s: %s", u, err)
+		}
+		if !reflect.DeepEqual(avatars[u], img) {
+			t.Fatalf("avatar mismatch for %s: %#v, %#v", avatars[u], img)
+		}
+	}
+}
+
 func compareImages(img1, img2 image.Image) float64 {
 	if !img1.Bounds().Eq(img2.Bounds()) {
 		return 0