290 lines
7.1 KiB
Go
290 lines
7.1 KiB
Go
// Package captcha provides an easy to use, unopinionated API for captcha generation
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package captcha
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import (
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"bytes"
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"github.com/golang/freetype"
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"github.com/golang/freetype/truetype"
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"golang.org/x/image/font"
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"image"
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"image/color"
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"image/draw"
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"image/png"
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"io"
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"math"
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"math/rand"
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"strconv"
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"time"
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)
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const charPreset = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789"
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var rng = rand.New(rand.NewSource(time.Now().UnixNano()))
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var ttfFont *truetype.Font
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// Options manage captcha generation details.
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type Options struct {
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// BackgroundColor is captcha image's background color.
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// It defaults to color.Transparent.
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BackgroundColor color.Color
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// CharPreset decides what text will be on captcha image.
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// It defaults to digit 0-9 and all English alphabet.
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// ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789
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CharPreset string
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// TextLength is the length of captcha text.
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// It defaults to 4.
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TextLength int
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// CurveNumber is the number of curves to draw on captcha image.
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// It defaults to 2.
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CurveNumber int
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// FontDPI controls DPI (dots per inch) of font.
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// The default is 72.0.
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FontDPI float64
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// FontScale controls the scale of font.
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// The default is 1.0.
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FontScale float64
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width int
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height int
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}
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func newDefaultOption(width, height int) *Options {
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return &Options{
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BackgroundColor: color.Transparent,
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CharPreset: charPreset,
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TextLength: 4,
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CurveNumber: 2,
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FontDPI: 72.0,
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FontScale: 1.0,
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width: width,
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height: height,
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}
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}
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// SetOption is a function that can be used to modify default options.
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type SetOption func(*Options)
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// Data is the result of captcha generation.
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// It has a `Text` field and a private `img` field that will
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// be used in `WriteImage` receiver
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type Data struct {
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// Text is captcha solution
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Text string
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img *image.NRGBA
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}
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// WriteImage encodes image data and writes to an io.Writer.
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// It returns possible error from PNG encoding
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func (data *Data) WriteImage(w io.Writer) error {
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return png.Encode(w, data.img)
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}
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func init() {
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ttfFont, _ = freetype.ParseFont(ttf)
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}
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// LoadFont let you load an external font.
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func LoadFont(fontData []byte) error {
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var err error
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ttfFont, err = freetype.ParseFont(fontData)
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return err
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}
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// LoadFontFromReader load an external font from an io.Reader interface.
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func LoadFontFromReader(reader io.Reader) error {
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var buf bytes.Buffer
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if _, err := io.Copy(&buf, reader); err != nil {
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return err
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}
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return LoadFont(buf.Bytes())
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}
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// New creates a new captcha.
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// It returns captcha data and any freetype drawing error encountered
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func New(width int, height int, option ...SetOption) (*Data, error) {
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options := newDefaultOption(width, height)
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for _, setOption := range option {
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setOption(options)
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}
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text := randomText(options)
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img := image.NewNRGBA(image.Rect(0, 0, width, height))
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draw.Draw(img, img.Bounds(), &image.Uniform{options.BackgroundColor}, image.ZP, draw.Src)
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drawNoise(img, options)
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drawCurves(img, options)
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err := drawText(text, img, options)
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if err != nil {
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return nil, err
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}
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return &Data{Text: text, img: img}, nil
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}
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// NewMathExpr creates a new captcha.
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// It will generate a image with a math expression like `1 + 2`
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func NewMathExpr(width int, height int, option ...SetOption) (*Data, error) {
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options := newDefaultOption(width, height)
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for _, setOption := range option {
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setOption(options)
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}
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text, equation := randomEquation()
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img := image.NewNRGBA(image.Rect(0, 0, width, height))
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draw.Draw(img, img.Bounds(), &image.Uniform{options.BackgroundColor}, image.ZP, draw.Src)
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drawNoise(img, options)
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drawCurves(img, options)
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err := drawText(equation, img, options)
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if err != nil {
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return nil, err
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}
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return &Data{Text: text, img: img}, nil
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}
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func randomText(opts *Options) (text string) {
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n := len(opts.CharPreset)
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for i := 0; i < opts.TextLength; i++ {
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text += string(opts.CharPreset[rng.Intn(n)])
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}
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return text
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}
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func drawNoise(img *image.NRGBA, opts *Options) {
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noiseCount := (opts.width * opts.height) / 28
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for i := 0; i < noiseCount; i++ {
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x := rng.Intn(opts.width)
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y := rng.Intn(opts.height)
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img.Set(x, y, randomColor())
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}
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}
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func randomColor() color.RGBA {
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red := rng.Intn(255)
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green := rng.Intn(255)
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blue := rng.Intn(255)
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return color.RGBA{R: uint8(red), G: uint8(green), B: uint8(blue), A: uint8(255)}
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}
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func drawCurves(img *image.NRGBA, opts *Options) {
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for i := 0; i < opts.CurveNumber; i++ {
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drawSineCurve(img, opts)
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}
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}
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// Ideally we want to draw bezier curves
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// For now sine curves will do the job
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func drawSineCurve(img *image.NRGBA, opts *Options) {
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var xStart, xEnd int
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if opts.width <= 40 {
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xStart, xEnd = 1, opts.width-1
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} else {
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xStart = rng.Intn(opts.width/10) + 1
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xEnd = opts.width - rng.Intn(opts.width/10) - 1
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}
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curveHeight := float64(rng.Intn(opts.height/6) + opts.height/6)
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yStart := rng.Intn(opts.height*2/3) + opts.height/6
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angle := 1.0 + rng.Float64()
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flip := rng.Intn(2) == 0
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yFlip := 1.0
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if flip {
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yFlip = -1.0
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}
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curveColor := randomInvertColor(opts.BackgroundColor)
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for x1 := xStart; x1 <= xEnd; x1++ {
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y := math.Sin(math.Pi*angle*float64(x1)/float64(opts.width)) * curveHeight * yFlip
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img.Set(x1, int(y)+yStart, curveColor)
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}
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}
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func drawText(text string, img *image.NRGBA, opts *Options) error {
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ctx := freetype.NewContext()
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ctx.SetDPI(opts.FontDPI)
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ctx.SetClip(img.Bounds())
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ctx.SetDst(img)
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ctx.SetHinting(font.HintingFull)
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ctx.SetFont(ttfFont)
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fontSpacing := opts.width / len(text)
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fontOffset := rng.Intn(fontSpacing / 2)
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for idx, char := range text {
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fontScale := 0.8 + rng.Float64()*0.4
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fontSize := float64(opts.height) / fontScale * opts.FontScale
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ctx.SetFontSize(fontSize)
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ctx.SetSrc(image.NewUniform(randomInvertColor(opts.BackgroundColor)))
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x := fontSpacing*idx + fontOffset
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y := opts.height/6 + rng.Intn(opts.height/3) + int(fontSize/2)
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pt := freetype.Pt(x, y)
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if _, err := ctx.DrawString(string(char), pt); err != nil {
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return err
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}
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}
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return nil
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}
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func randomInvertColor(base color.Color) color.Color {
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baseLightness := getLightness(base)
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var value float64
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if baseLightness >= 0.5 {
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value = baseLightness - 0.3 - rng.Float64()*0.2
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} else {
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value = baseLightness + 0.3 + rng.Float64()*0.2
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}
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hue := float64(rng.Intn(361)) / 360
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saturation := 0.6 + rng.Float64()*0.2
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return hsva{h: hue, s: saturation, v: value, a: uint8(255)}
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}
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func getLightness(colour color.Color) float64 {
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r, g, b, a := colour.RGBA()
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// transparent
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if a == 0 {
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return 1.0
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}
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max := maxColor(r, g, b)
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min := minColor(r, g, b)
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l := (float64(max) + float64(min)) / (2 * 255)
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return l
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}
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func maxColor(numList ...uint32) (max uint32) {
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for _, num := range numList {
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colorVal := num & 255
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if colorVal > max {
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max = colorVal
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}
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}
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return max
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}
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func minColor(numList ...uint32) (min uint32) {
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min = 255
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for _, num := range numList {
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colorVal := num & 255
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if colorVal < min {
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min = colorVal
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}
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}
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return min
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}
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func randomEquation() (text string, equation string) {
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left := 1 + rng.Intn(9)
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right := 1 + rng.Intn(9)
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text = strconv.Itoa(left + right)
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equation = strconv.Itoa(left) + "+" + strconv.Itoa(right)
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return text, equation
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}
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