add: draw font and curves

captcha.go

@@ -1,18 +1,27 @@
 package captcha
 
 import (
+	"github.com/golang/freetype"
+	"github.com/golang/freetype/truetype"
+	"golang.org/x/image/font"
+	"golang.org/x/image/font/gofont/goregular"
 	"image"
 	"image/color"
+	"image/draw"
 	"image/png"
 	"io"
+	"math"
 	"math/rand"
 	"time"
 )
 
 const charPreset = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789"
 
+var rng = rand.New(rand.NewSource(time.Now().UnixNano()))
+var ttfFont *truetype.Font
+
 type Options struct {
-	BackgroundColor color.RGBA
+	BackgroundColor color.Color
 	CharPreset      string
 	TxtLength       int
 	width           int
@@ -21,14 +30,15 @@ type Options struct {
 
 func newDefaultOption(width, height int) *Options {
 	return &Options{
-		CharPreset: charPreset,
-		TxtLength:  4,
-		width:      width,
-		height:     height,
+		BackgroundColor: color.Transparent,
+		CharPreset:      charPreset,
+		TxtLength:       4,
+		width:           width,
+		height:          height,
 	}
 }
 
-type Option func(*Options)
+type SetOption func(*Options)
 
 type Data struct {
 	Text string
@@ -40,7 +50,15 @@ func (data *Data) WriteTo(w io.Writer) error {
 	return png.Encode(w, data.img)
 }
 
-func New(width int, height int, option ...Option) *Data {
+func init() {
+	var err error
+	ttfFont, err = freetype.ParseFont(goregular.TTF)
+	if err != nil {
+		panic(err)
+	}
+}
+
+func New(width int, height int, option ...SetOption) (*Data, error) {
 	options := newDefaultOption(width, height)
 	for _, setOption := range option {
 		setOption(options)
@@ -48,14 +66,19 @@ func New(width int, height int, option ...Option) *Data {
 
 	text := randomText(options)
 	img := image.NewNRGBA(image.Rect(0, 0, width, height))
+	draw.Draw(img, img.Bounds(), &image.Uniform{options.BackgroundColor}, image.ZP, draw.Src)
 	drawNoise(img, options)
+	drawLine(img, options)
+	err := drawText(text, img, options)
+	if err != nil {
+		return nil, err
+	}
 
-	return &Data{Text: text, img: img}
+	return &Data{Text: text, img: img}, nil
 }
 
 func randomText(opts *Options) (text string) {
 	n := len(opts.CharPreset)
-	rng := rand.New(rand.NewSource(time.Now().UnixNano()))
 	for i := 0; i < opts.TxtLength; i++ {
 		text += string(opts.CharPreset[rng.Intn(n)])
 	}
@@ -64,7 +87,6 @@ func randomText(opts *Options) (text string) {
 }
 
 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)
@@ -74,10 +96,73 @@ func drawNoise(img *image.NRGBA, opts *Options) {
 }
 
 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)}
 }
+
+func drawLine(img *image.NRGBA, opts *Options) {
+	for i := 0; i < 3; i++ {
+		drawSineCurve(img, opts)
+	}
+}
+
+// Ideally we want to draw bezier curves
+// For now sine curves will do the job
+func drawSineCurve(img *image.NRGBA, opts *Options) {
+	var xStart, xEnd int
+	if opts.width <= 40 {
+		xStart, xEnd = 1, opts.width-1
+	} else {
+		xStart = rng.Intn(opts.width/10) + 1
+		xEnd = opts.width - rng.Intn(opts.width/10) - 1
+	}
+	curveHeight := float64(rng.Intn(opts.height/6) + opts.height/6)
+	yStart := rng.Intn(opts.height*2/3) + opts.height/6
+	angle := 1.0 + rng.Float64()
+	flip := rng.Intn(2) == 0
+	yFlip := 1.0
+	if flip {
+		yFlip = -1.0
+	}
+	curveColor := randomDarkGray()
+
+	for x1 := xStart; x1 <= xEnd; x1++ {
+		y := math.Sin(math.Pi*angle*float64(x1)/float64(opts.width)) * curveHeight * yFlip
+		img.Set(x1, int(y)+yStart, curveColor)
+	}
+}
+
+func randomDarkGray() color.Gray {
+	gray := rng.Intn(128) + 20
+
+	return color.Gray{Y: uint8(gray)}
+}
+
+func drawText(text string, img *image.NRGBA, opts *Options) error {
+	ctx := freetype.NewContext()
+	ctx.SetDPI(72.0)
+	ctx.SetClip(img.Bounds())
+	ctx.SetDst(img)
+	ctx.SetHinting(font.HintingFull)
+	ctx.SetFont(ttfFont)
+
+	fontSpacing := opts.width / len(text)
+
+	for idx, char := range text {
+		fontScale := 1 + float64(rng.Intn(7))/float64(9)
+		fontSize := float64(opts.height) / fontScale
+		ctx.SetFontSize(fontSize)
+		ctx.SetSrc(image.NewUniform(randomDarkGray()))
+		x := fontSpacing*idx + fontSpacing/int(fontSize)
+		y := opts.height/6 + rng.Intn(opts.height/3) + int(fontSize/2)
+		pt := freetype.Pt(x, y)
+		if _, err := ctx.DrawString(string(char), pt); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}

example/index.html

@@ -0,0 +1,10 @@
+<!DOCTYPE html>
+<html lang="en">
+<head>
+    <meta charset="UTF-8">
+    <title>Captcha</title>
+</head>
+<body>
+    <img src="/captcha" alt="captcha">
+</body>
+</html>

example/main.go

@@ -0,0 +1,37 @@
+package main
+
+import (
+	"fmt"
+	"github.com/steambap/captcha"
+	"html/template"
+	"net/http"
+)
+
+func main() {
+	http.HandleFunc("/", IndexHandle)
+	http.HandleFunc("/captcha", CaptchaHandle)
+	fmt.Println("Server start at port 8080")
+	err := http.ListenAndServe(":8080", nil)
+	if err != nil {
+		panic(err)
+	}
+}
+
+func IndexHandle(w http.ResponseWriter, _ *http.Request) {
+	doc, err := template.ParseFiles("index.html")
+	if err != nil {
+		fmt.Fprint(w, err.Error())
+		return
+	}
+	doc.Execute(w, nil)
+}
+
+func CaptchaHandle(w http.ResponseWriter, _ *http.Request) {
+	img, err := captcha.New(150, 50)
+	if err != nil {
+		fmt.Fprint(w, nil)
+		fmt.Println(err.Error())
+		return
+	}
+	img.WriteTo(w)
+}