add: draw noise

captcha.go

@@ -1,10 +1,10 @@
 package captcha
 
 import (
-	"io"
-	"image/color"
 	"image"
+	"image/color"
 	"image/png"
+	"io"
 	"math/rand"
 	"time"
 )
@@ -15,12 +15,16 @@ type Options struct {
 	BackgroundColor color.RGBA
 	CharPreset      string
 	TxtLength       int
+	width           int
+	height          int
 }
 
-func newDefaultOption() *Options {
+func newDefaultOption(width, height int) *Options {
 	return &Options{
 		CharPreset: charPreset,
 		TxtLength:  4,
+		width:      width,
+		height:     height,
 	}
 }
 
@@ -37,23 +41,43 @@ func (data *Data) WriteTo(w io.Writer) error {
 }
 
 func New(width int, height int, option ...Option) *Data {
-	options := newDefaultOption()
+	options := newDefaultOption(width, height)
 	for _, setOption := range option {
 		setOption(options)
 	}
 
 	text := randomText(options)
 	img := image.NewNRGBA(image.Rect(0, 0, width, height))
+	drawNoise(img, options)
 
 	return &Data{Text: text, img: img}
 }
 
 func randomText(opts *Options) (text string) {
 	n := len(opts.CharPreset)
-	r := rand.New(rand.NewSource(time.Now().UnixNano()))
+	rng := rand.New(rand.NewSource(time.Now().UnixNano()))
 	for i := 0; i < opts.TxtLength; i++ {
-		text += string(opts.CharPreset[r.Intn(n)])
+		text += string(opts.CharPreset[rng.Intn(n)])
 	}
 
 	return text
 }
+
+func drawNoise(img *image.NRGBA, opts *Options) {
+	rng := rand.New(rand.NewSource(time.Now().UnixNano()))
+	noiseCount := (opts.width * opts.height) / 18
+	for i := 0; i < noiseCount; i++ {
+		x := rng.Intn(opts.width)
+		y := rng.Intn(opts.height)
+		img.Set(x, y, randomColor())
+	}
+}
+
+func randomColor() color.RGBA {
+	rng := rand.New(rand.NewSource(time.Now().UnixNano()))
+	red := rng.Intn(255)
+	green := rng.Intn(255)
+	blue := rng.Intn(255)
+
+	return color.RGBA{R: uint8(red), G: uint8(green), B: uint8(blue), A: uint8(255)}
+}