golang 防知乎 中文验证码 源码

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最开始用图形来模仿文字进行各种角度的倒立和排列，后来切换为文字后，有很多问题。总结如下：

1、程序在画图形和画文字方面不一样，图形的是从原点开始（0,0），而文字则从文字的基线开始（0,baseline）

2、在增加角度偏移时，文字或图形的高宽会产生变化（偏∠45度时达到最大），这时候为了让它们顶点对齐，需要计算偏移量（用三角函数）

3、在绘图时，会先旋转“画布”(描述可能不准确)，再绘制文字。此时要往回旋转，否则下一个图形会顺着这个角度继续画。

4、为了让图形保持固定宽度，对于有偏角的文字，需要平均缩小左右间距（否则不同的角度，固定的文字个数，会让图形宽度不同）

效果图：

源码：（代码还可以再整理和优化，但限于计划时间，懒得弄了）

package main

import ( 
	"math"
	"reflect"
	"time"
	"math/rand"
	"github.com/golang/freetype/truetype"
	"github.com/fogleman/gg" // 需要安装这个包
    "flag" 
    "fmt" 
    "io/ioutil" 
    "log" 
)

var wORDSLIB = []interface{}{"赵","钱","孙","李","周","吴","郑","冯","陈","褚","卫","蒋","沈","韩","杨","朱","秦","尤","许","何","吕","施","张","孔","曹","严","华","金","魏","陶","姜","戚","谢","邹","喻","柏","水","窦","章","云","苏","潘","葛","奚","范","彭","郎","鲁","韦","昌","马","苗","凤","花","方","俞","任","袁","柳","酆","鲍","史","唐","费","廉","岑","薛","雷","贺","倪","汤","滕","殷","罗","毕","郝","邬","安","常","乐","于","时","傅","皮","卞","齐","康","伍","余","元","卜","顾","孟","平","黄","和","穆","萧","尹","姚","邵","湛","汪","祁","毛","禹","狄","米","贝","明","臧","计","伏","成","戴","谈","宋","茅","庞","熊","纪","舒","屈","项","祝","董","梁","杜","阮","蓝","闵","席","季","麻","强","贾","路","娄","危","江","童","颜","郭","梅","盛","林","刁","钟","徐","邱","骆","高","夏","蔡","樊","胡","凌","霍","虞","万","支","柯","昝","管","卢","莫","经","房","裘","缪","干","解","应","宗","丁","宣","贲","邓","郁","单","杭","洪","包","诸","左","石","崔","吉","钮","龚","程","嵇","邢","滑","裴","陆","荣","翁","荀","羊","於","惠","甄","曲","家","封","芮","羿","储","靳","汲","邴","糜","松","井","段","富","巫","乌","焦","巴","弓","牧","隗","山","谷","车","侯","宓","蓬","全","郗","班","仰","秋","仲","伊","宫","宁","仇","栾","暴","甘","钭","厉","戎","祖","武","符","刘","景","詹","束","龙","叶","幸","司","韶","郜","黎","蓟","薄","印","宿","白","怀","蒲","邰","从","鄂","索","咸","籍","赖","卓","蔺","屠","蒙","池","乔","阴","鬱","胥","能","苍","双","闻","莘","党","翟","谭","贡","劳","逄","姬","扶","堵","冉","宰","郦","雍","卻","璩","桑","桂","濮","牛","寿","通","边","扈","燕","冀","郏","浦","尚","农","温","别","庄","晏","柴","瞿","阎","充","慕","连","茹","习","宦","艾","鱼","容","向","古","易","慎","戈","廖","庾","终","暨","居","衡","步","都","耿","满","弘","匡","国","文","寇","广","禄","阙","东","欧","殳","沃","利","蔚","越","夔","隆","师","巩","厍","聂","晁","勾","敖","融","冷","訾","辛","阚","那","简","饶","空","曾","毋","沙","乜","养","鞠","须","丰","巢","关","蒯","相","查","后","荆","红","游","竺","权","逯","盖","益","桓","公","俟","上","官","阳","人","赫","皇","甫","尉","迟","澹","台","冶","政","淳","太","叔","申","轩","辕","令","狐","离","宇","长","鲜","闾","丘","徒","仉","督","子","颛","端","木","西","漆","雕","正","壤","驷","良","拓","跋","夹","父","晋","楚","闫","法","汝","鄢","涂","钦","百","里","南","门","呼","延","归","海","舌","微","生","岳","帅","缑","亢","况","郈","有","琴","商","牟","佘","佴","伯","赏","墨","哈","谯","笪","年","爱","佟","第","五","言","福","姓"}

var ( 
    dpi      = flag.Float64("dpi", 72, "screen resolution in Dots Per Inch") 
    fontfile = flag.String("fontfile", "./SIMYOU.TTF", "filename of the ttf font") 
    size     = flag.Float64("size", 40, "font size in points") 
)

func main() { 
	x := "abc"
	fmt.Println(x[0:3])
    drawImageBygg()
} 

func drawImageBygg(){
	dc := gg.NewContext(320, 56)  // 56 => w*sin(45) + h*sin(45)  45度时，字体达到最大高度
	dc.SetRGBA(1, 1, 1,0) // 设置背景色：末尾为透明度 1-0(1-不透明 0-透明)
	dc.Clear()
	dc.SetRGBA(0, 0, 0,1) // 设置字体色

	fontBytes, err := ioutil.ReadFile(*fontfile) 
    if err != nil { 
        log.Println(err) 
        return 
    } 
	font, err := truetype.Parse(fontBytes)
	if err != nil {
        log.Println(err) 
        return 
	}
	face := truetype.NewFace(font, &truetype.Options{
		Size: *size,
		DPI:*dpi,
	}) 
	dc.SetFontFace(face)

	// 初始化用于计算坐标的变量
	fm := face.Metrics()
	ascent := float64(fm.Ascent.Round()) // 字体的基线到顶部距离
	decent := float64(fm.Descent.Round()) // 字体的基线到底部的距离
	w := float64(fm.Height.Round()) // 方块字，大多数应为等宽字，即和高度一样
	h := float64(fm.Height.Round())
	totalWidth := 0.0 // 目前已累积的图片宽度（需要用来计算字体位置）

	// 随机取汉字，定位倒立的字
	words := getRandomMembersFromMemberLibary(wORDSLIB,8) // 取8个字
	reverseWordsIndex := getRandomMembersFromMemberLibary([]interface{}{0,1,2,3,4,5,6,7},2) // 随机2个倒立字

	for i,word := range words{
		degree := If(Contain(i,reverseWordsIndex),float64(RandInt64(150,210)),float64(RandInt64(-30,30))) // 随机角度，正向角度 -30~30，倒立角度 150~210
		x,y,leftCutSize,rightCS := getCoordByQuadrantAndDegree(w,h,ascent,decent,degree,totalWidth)
		dc.RotateAbout(gg.Radians(degree),0,0)
		dc.DrawStringAnchored(word.(string), x,y, 0,0)
		dc.RotateAbout(-1*gg.Radians(degree),0,0)
		totalWidth = totalWidth + leftCutSize + rightCS
		fmt.Println("x:",x,"y:",y,"total:",totalWidth,"degree:",degree)
	}

	dc.Stroke()
	dc.SavePNG("out.png")
    fmt.Println("Wrote out.png OK.") 
}

func getCoordByQuadrantAndDegree(w,h,ascent,descent,degree,beforTotalWidth float64)(x,y,leftCutSize,rightCutSize float64){
	var totalWidth float64
	switch{
		case degree<=0 && degree >= -40:  // 第一象限：逆时针 -30度 ~ 0  <=>  330 ~ 360 （目前参数要传入负数）  
			rd := -1 * degree // 转为正整数，便于计算
			leftCutSize = w*getDegreeSin(90-rd)
			rightCutSize = h*getDegreeSin(rd)
			
			offset := (leftCutSize + rightCutSize - w) / 2 // 横向偏移量（角度倾斜越厉害，占宽越多，通过偏移量分摊给它的左右边距来收窄）
			leftCutSize,rightCutSize = leftCutSize - offset,rightCutSize - offset

			totalWidth = beforTotalWidth + leftCutSize 
			x = getDegreeSin(90 - rd)*totalWidth - w 
			y = ascent + getDegreeSin(rd)*totalWidth  
		case degree >=0 && degree <= 40:  // 第四象限：顺时针 0 ~ 30度
			leftCutSize = h*getDegreeSin(degree)
			rightCutSize = w*getDegreeSin(90-degree)

			offset := (leftCutSize + rightCutSize - w) / 2
			leftCutSize,rightCutSize = leftCutSize - offset,rightCutSize - offset

			totalWidth = beforTotalWidth + leftCutSize // 现在totalwidth = 前面的宽 + 自己的左切边
			x = getDegreeSin(90-degree)*totalWidth
			y = ascent - getDegreeSin(degree)*totalWidth 
		case degree >= 180 && degree <= 220:  // 第二象限：顺时针 180 ~ 210度
			rd := degree - 180
			leftCutSize = h*getDegreeSin(rd)
			rightCutSize = w*getDegreeSin(90-rd)

			offset := (leftCutSize + rightCutSize - w) / 2 
			leftCutSize,rightCutSize = leftCutSize - offset,rightCutSize - offset

			totalWidth = beforTotalWidth + leftCutSize 
			x = -1 * (getDegreeSin(90-rd)*totalWidth + w)
			y = getDegreeSin(rd)*totalWidth - descent
		case degree >= 140 && degree <= 180:  // 第三象限：顺时针 150 ~ 180度
			rd := 180-degree
			leftCutSize = w*getDegreeSin(90-rd)
			rightCutSize = h*getDegreeSin(rd)

			offset := (leftCutSize + rightCutSize - w) / 2
			leftCutSize,rightCutSize = leftCutSize - offset,rightCutSize - offset
			
			totalWidth = beforTotalWidth + leftCutSize 
			x = -1 * (getDegreeSin(90-rd) * totalWidth)
			y = -1 * (getDegreeSin(rd) * totalWidth + descent)
		default: panic(fmt.Sprintf("非法的参数：%f",degree))
	}
	return
}

func getDegreeSin(degree float64) float64{
	return math.Sin(degree*math.Pi/180)
}

//RandInt64 ...
func RandInt64(min, max int64) int64 {
	if min >= max || min == 0 || max == 0 {
		return max
	}
	rand.Seed(time.Now().UnixNano())
	return rand.Int63n(max-min) + min
}

func getRandomMembersFromMemberLibary(lib []interface{},size int)[]interface{}{
	source,result := make([]interface{},0),make([]interface{},0)
	if size <= 0 || len(lib) == 0{
		return result
	}
	for _,v := range lib{
		source = append(source,v)
	}
	if size >= len(lib){
		return source
	}
	for i:=0;i<size;i++{
		rand.Seed(time.Now().UnixNano())
		pos := rand.Intn(len(source))
		result = append(result,source[pos])
		source = append(source[:pos], source[pos+1:]...)
	}
	return result
}

//Contain ...
func Contain(obj interface{}, target interface{}) bool {
    targetValue := reflect.ValueOf(target)
    switch reflect.TypeOf(target).Kind() {
    case reflect.Slice, reflect.Array:
        for i := 0; i < targetValue.Len(); i++ {
            if targetValue.Index(i).Interface() == obj {
                return true
            }
        }
    case reflect.Map:
        if targetValue.MapIndex(reflect.ValueOf(obj)).IsValid() {
            return true
        }
    }

    return false
}

//If ...
func If(expr bool,trueVal float64,falseVal float64) float64{
	if expr {
		return trueVal 
	}
	return falseVal
}

　　

 需要一个字体文件，这里使用的幼圆（幼圆免费，其他免费字体懒得找）。

注意：字体不同，宽度和高度可能会需要调整。