captcha.go

package gocaptcha

import (
	"errors"
	"image"
	"image/color"
	"image/draw"
	"image/gif"
	"image/jpeg"
	"image/png"
	"io"
	"math/rand"
)

const (
	// DefaultDPI 默认的dpi
	DefaultDPI = 72.0
	// DefaultBlurKernelSize 默认模糊卷积核大小
	DefaultBlurKernelSize = 2
	// DefaultBlurSigma 默认模糊sigma值
	DefaultBlurSigma = 0.65
	// DefaultAmplitude 默认图片扭曲的振幅
	DefaultAmplitude = 20
	//DefaultFrequency 默认图片扭曲的波频率
	DefaultFrequency = 0.05
)

var TextCharacters = []rune("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789")

const (
	ImageFormatPng ImageFormat = iota
	ImageFormatJpeg
	ImageFormatGif
)

// ImageFormat 图片格式
type ImageFormat int

type CaptchaImage struct {
	nrgba   *image.NRGBA
	width   int
	height  int
	Complex int
	Error   error
}

// New 新建一个图片对象
func New(width int, height int, bgColor color.RGBA) *CaptchaImage {
	m := image.NewNRGBA(image.Rect(0, 0, width, height))

	draw.Draw(m, m.Bounds(), &image.Uniform{C: bgColor}, image.Point{}, draw.Src)

	return &CaptchaImage{
		nrgba:  m,
		height: height,
		width:  width,
	}
}

// Encode 编码图片
func (captcha *CaptchaImage) Encode(w io.Writer, imageFormat ImageFormat) error {

	if imageFormat == ImageFormatPng {
		return png.Encode(w, captcha.nrgba)
	}
	if imageFormat == ImageFormatJpeg {
		return jpeg.Encode(w, captcha.nrgba, &jpeg.Options{Quality: 100})
	}
	if imageFormat == ImageFormatGif {
		return gif.Encode(w, captcha.nrgba, &gif.Options{NumColors: 256})
	}

	return errors.New("not supported image format")
}

// DrawLine 画直线.
func (captcha *CaptchaImage) DrawLine(drawer LineDrawer, lineColor color.Color) *CaptchaImage {
	if captcha.Error != nil {
		return captcha
	}
	y := captcha.nrgba.Bounds().Dy()
	point1 := image.Point{X: captcha.nrgba.Bounds().Min.X + 1, Y: rand.Intn(y)}
	point2 := image.Point{X: captcha.nrgba.Bounds().Max.X - 1, Y: rand.Intn(y)}
	captcha.Error = drawer.DrawLine(captcha.nrgba, point1, point2, lineColor)
	return captcha
}

// DrawBorder 画边框.
func (captcha *CaptchaImage) DrawBorder(borderColor color.RGBA) *CaptchaImage {
	if captcha.Error != nil {
		return captcha
	}
	for x := 0; x < captcha.width; x++ {
		captcha.nrgba.Set(x, 0, borderColor)
		captcha.nrgba.Set(x, captcha.height-1, borderColor)
	}
	for y := 0; y < captcha.height; y++ {
		captcha.nrgba.Set(0, y, borderColor)
		captcha.nrgba.Set(captcha.width-1, y, borderColor)
	}
	return captcha
}

// DrawNoise 画噪点.
func (captcha *CaptchaImage) DrawNoise(complex NoiseDensity, noiseDrawer NoiseDrawer) *CaptchaImage {
	if captcha.Error != nil {
		return captcha
	}
	captcha.Error = noiseDrawer.DrawNoise(captcha.nrgba, complex)
	return captcha
}

// DrawText 写字.
func (captcha *CaptchaImage) DrawText(textDrawer TextDrawer, text string) *CaptchaImage {
	if captcha.Error != nil {
		return captcha
	}
	captcha.Error = textDrawer.DrawString(captcha.nrgba, text)
	return captcha
}

// DrawBlur 对图片进行模糊处理
func (captcha *CaptchaImage) DrawBlur(drawer BlurDrawer, kernelSize int, sigma float64) *CaptchaImage {
	if captcha.Error != nil {
		return captcha
	}
	captcha.Error = drawer.DrawBlur(captcha.nrgba, kernelSize, sigma)
	return captcha
}