266 lines
8.0 KiB
Go
266 lines
8.0 KiB
Go
// Package captcha 生成登录页用的图形验证码。
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//
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// 刻意不引第三方库、也不依赖字体文件：字形是内置的 5×7 点阵，放大后逐个加抖动，
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// 再叠干扰线与噪点。服务端只存答案（不存图片），答案一次性使用并带过期时间。
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package captcha
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import (
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"bytes"
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"crypto/rand"
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"encoding/base64"
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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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"math/big"
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mrand "math/rand"
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"strings"
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"sync"
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"time"
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)
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const (
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// alphabet 是取码字符集：去掉 0/O、1/I/L 这些互相像的，省得用户反复认错。
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alphabet = "23456789ABCDEFGHJKLMNPQRSTUVWXYZ"
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// CodeLen 是验证码长度。
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CodeLen = 4
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glyphW, glyphH = 5, 7
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scale = 4
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padX, padY = 10, 6
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// stepX 要给抖动留余量：字符宽 20，抖动 ±2，步长 26 时最小间距只剩 2px，
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// 相邻字符的笔画会串在一起（人眼也一样难看）。30 保证最小间距仍有 6px。
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stepX = 30
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// Width/Height 是出图尺寸。
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Width = padX*2 + (CodeLen-1)*stepX + glyphW*scale // 130
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Height = padY*2 + glyphH*scale // 40
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defaultTTL = 10 * time.Minute
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maxItems = 4096
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)
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// Store 保存待验证的答案。站点是单进程部署，放内存即可；
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// 重启会让已发出的验证码失效，用户重新获取一次就行。
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type Store struct {
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mu sync.Mutex
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items map[string]item
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ttl time.Duration
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}
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type item struct {
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code string
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exp time.Time
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}
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// NewStore 建一个验证码池；ttl <= 0 时用 10 分钟。
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func NewStore(ttl time.Duration) *Store {
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if ttl <= 0 {
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ttl = defaultTTL
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}
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return &Store{items: map[string]item{}, ttl: ttl}
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}
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// Issue 生成一张新验证码，返回用于对答的 id 与 PNG 字节。
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func (s *Store) Issue() (string, []byte, error) {
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code, err := randomCode()
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if err != nil {
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return "", nil, err
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}
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id, err := randomID()
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if err != nil {
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return "", nil, err
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}
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s.mu.Lock()
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s.pruneLocked()
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s.items[id] = item{code: code, exp: time.Now().Add(s.ttl)}
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s.mu.Unlock()
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png, err := render(code)
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if err != nil {
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return "", nil, err
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}
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return id, png, nil
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}
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// Verify 校验答案。无论对错都作废该 id——一次一用，避免拿同一张图反复试。
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func (s *Store) Verify(id, answer string) bool {
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s.mu.Lock()
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it, ok := s.items[id]
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delete(s.items, id)
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s.mu.Unlock()
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if !ok || time.Now().After(it.exp) {
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return false
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}
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got := strings.ToUpper(strings.TrimSpace(answer))
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return got == it.code
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}
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// Answer 返回某个 id 当前对应的答案，不作废它。
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// 只给测试与本地排查用：答案本身不会经任何接口下发到客户端。
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func (s *Store) Answer(id string) (string, bool) {
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s.mu.Lock()
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defer s.mu.Unlock()
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it, ok := s.items[id]
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return it.code, ok
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}
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// pruneLocked 清掉过期项；仍然超过上限时随便丢一些，防止有人只取图不对答把内存撑大。
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// 调用方需持有 s.mu。
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func (s *Store) pruneLocked() {
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now := time.Now()
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for k, v := range s.items {
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if now.After(v.exp) {
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delete(s.items, k)
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}
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}
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for k := range s.items {
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if len(s.items) < maxItems {
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break
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}
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delete(s.items, k)
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}
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}
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func randomCode() (string, error) {
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var b strings.Builder
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for i := 0; i < CodeLen; i++ {
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n, err := rand.Int(rand.Reader, big.NewInt(int64(len(alphabet))))
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if err != nil {
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return "", err
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}
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b.WriteByte(alphabet[n.Int64()])
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}
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return b.String(), nil
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}
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func randomID() (string, error) {
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var b [16]byte
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if _, err := rand.Read(b[:]); err != nil {
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return "", err
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}
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return base64.RawURLEncoding.EncodeToString(b[:]), nil
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}
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// render 把验证码画成 PNG：底 → 干扰线 → 字符（各自抖动）→ 噪点。
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func render(code string) ([]byte, error) {
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img := image.NewRGBA(image.Rect(0, 0, Width, Height))
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draw.Draw(img, img.Bounds(), &image.Uniform{color.RGBA{248, 250, 251, 255}}, image.Point{}, draw.Src)
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for i := 0; i < 3; i++ {
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drawLine(img, mrand.Intn(Width), mrand.Intn(Height), mrand.Intn(Width), mrand.Intn(Height), rgb(160, 215))
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}
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for i, ch := range code {
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g, ok := glyphs[ch]
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if !ok {
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continue
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}
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// 每个字符独立抖动，位置与颜色都不同——不抖的话点阵字太规整，等于白送
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ox := padX + i*stepX + mrand.Intn(5) - 2
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oy := padY + mrand.Intn(5) - 2
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col := rgb(0, 110)
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for row := 0; row < glyphH; row++ {
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for c := 0; c < glyphW; c++ {
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if g[row]&(1<<uint(glyphW-1-c)) == 0 {
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continue
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}
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for dy := 0; dy < scale; dy++ {
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for dx := 0; dx < scale; dx++ {
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img.Set(ox+c*scale+dx, oy+row*scale+dy, col)
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}
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}
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}
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}
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}
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// 压在最上面的噪点少一些，别把字盖住
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for i := 0; i < 60; i++ {
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img.Set(mrand.Intn(Width), mrand.Intn(Height), rgb(120, 200))
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}
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var buf bytes.Buffer
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if err := png.Encode(&buf, img); err != nil {
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return nil, err
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}
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return buf.Bytes(), nil
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}
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// rgb 返回每个通道取 [lo, hi) 的随机颜色。
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func rgb(lo, hi int) color.RGBA {
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f := func() uint8 { return uint8(lo + mrand.Intn(hi-lo)) }
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return color.RGBA{f(), f(), f(), 255}
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}
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// drawLine 是 Bresenham 画线（只用标准库，不引画图包）。
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func drawLine(img *image.RGBA, x0, y0, x1, y1 int, c color.RGBA) {
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dx, dy := abs(x1-x0), -abs(y1-y0)
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sx, sy := -1, -1
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if x0 < x1 {
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sx = 1
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}
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if y0 < y1 {
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sy = 1
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}
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err := dx + dy
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for {
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img.Set(x0, y0, c)
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if x0 == x1 && y0 == y1 {
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return
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}
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e2 := 2 * err
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if e2 >= dy {
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err += dy
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x0 += sx
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}
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if e2 <= dx {
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err += dx
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y0 += sy
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}
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}
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}
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func abs(v int) int {
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if v < 0 {
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return -v
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}
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return v
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}
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// glyphs 是 5×7 点阵字形：每行低 5 位有效，最高位在最左边。
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var glyphs = map[rune][glyphH]byte{
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'0': {0b01110, 0b10001, 0b10011, 0b10101, 0b11001, 0b10001, 0b01110},
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'1': {0b00100, 0b01100, 0b00100, 0b00100, 0b00100, 0b00100, 0b01110},
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'2': {0b01110, 0b10001, 0b00001, 0b00010, 0b00100, 0b01000, 0b11111},
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'3': {0b11111, 0b00010, 0b00100, 0b00010, 0b00001, 0b10001, 0b01110},
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'4': {0b00010, 0b00110, 0b01010, 0b10010, 0b11111, 0b00010, 0b00010},
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'5': {0b11111, 0b10000, 0b11110, 0b00001, 0b00001, 0b10001, 0b01110},
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'6': {0b00110, 0b01000, 0b10000, 0b11110, 0b10001, 0b10001, 0b01110},
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'7': {0b11111, 0b00001, 0b00010, 0b00100, 0b01000, 0b01000, 0b01000},
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'8': {0b01110, 0b10001, 0b10001, 0b01110, 0b10001, 0b10001, 0b01110},
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'9': {0b01110, 0b10001, 0b10001, 0b01111, 0b00001, 0b00010, 0b01100},
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'A': {0b01110, 0b10001, 0b10001, 0b11111, 0b10001, 0b10001, 0b10001},
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'B': {0b11110, 0b10001, 0b10001, 0b11110, 0b10001, 0b10001, 0b11110},
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'C': {0b01110, 0b10001, 0b10000, 0b10000, 0b10000, 0b10001, 0b01110},
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'D': {0b11110, 0b10001, 0b10001, 0b10001, 0b10001, 0b10001, 0b11110},
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'E': {0b11111, 0b10000, 0b10000, 0b11110, 0b10000, 0b10000, 0b11111},
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'F': {0b11111, 0b10000, 0b10000, 0b11110, 0b10000, 0b10000, 0b10000},
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'G': {0b01110, 0b10001, 0b10000, 0b10111, 0b10001, 0b10001, 0b01111},
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'H': {0b10001, 0b10001, 0b10001, 0b11111, 0b10001, 0b10001, 0b10001},
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'I': {0b01110, 0b00100, 0b00100, 0b00100, 0b00100, 0b00100, 0b01110},
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'J': {0b00111, 0b00010, 0b00010, 0b00010, 0b00010, 0b10010, 0b01100},
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'K': {0b10001, 0b10010, 0b10100, 0b11000, 0b10100, 0b10010, 0b10001},
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'L': {0b10000, 0b10000, 0b10000, 0b10000, 0b10000, 0b10000, 0b11111},
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'M': {0b10001, 0b11011, 0b10101, 0b10101, 0b10001, 0b10001, 0b10001},
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'N': {0b10001, 0b11001, 0b10101, 0b10011, 0b10001, 0b10001, 0b10001},
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'O': {0b01110, 0b10001, 0b10001, 0b10001, 0b10001, 0b10001, 0b01110},
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'P': {0b11110, 0b10001, 0b10001, 0b11110, 0b10000, 0b10000, 0b10000},
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'Q': {0b01110, 0b10001, 0b10001, 0b10001, 0b10101, 0b10010, 0b01101},
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'R': {0b11110, 0b10001, 0b10001, 0b11110, 0b10100, 0b10010, 0b10001},
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'S': {0b01111, 0b10000, 0b10000, 0b01110, 0b00001, 0b00001, 0b11110},
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'T': {0b11111, 0b00100, 0b00100, 0b00100, 0b00100, 0b00100, 0b00100},
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'U': {0b10001, 0b10001, 0b10001, 0b10001, 0b10001, 0b10001, 0b01110},
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'V': {0b10001, 0b10001, 0b10001, 0b10001, 0b10001, 0b01010, 0b00100},
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'W': {0b10001, 0b10001, 0b10001, 0b10101, 0b10101, 0b11011, 0b10001},
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'X': {0b10001, 0b10001, 0b01010, 0b00100, 0b01010, 0b10001, 0b10001},
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'Y': {0b10001, 0b10001, 0b01010, 0b00100, 0b00100, 0b00100, 0b00100},
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'Z': {0b11111, 0b00001, 0b00010, 0b00100, 0b01000, 0b10000, 0b11111},
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}
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