微信小程序生成条形码

以下是处理过 wx.createCanvasContext()的，可以直接用

1. utils下新增barCode.js

var CHAR_TILDE = 126;
var CODE_FNC1 = 102;

var SET_STARTA = 103;
var SET_STARTB = 104;
var SET_STARTC = 105;
var SET_SHIFT = 98;
var SET_CODEA = 101;
var SET_CODEB = 100;
var SET_STOP = 106;


var REPLACE_CODES = {
  CHAR_TILDE: CODE_FNC1 //~ corresponds to FNC1 in GS1-128 standard
}

var CODESET = {
  ANY: 1,
  AB: 2,
  A: 3,
  B: 4,
  C: 5
};

function getBytes(str) {
  var bytes = [];
  for (var i = 0; i < str.length; i++) {
    bytes.push(str.charCodeAt(i));
  }
  return bytes;
}

exports.code128 = function (ctx, text, width, height) {

  width = parseInt(width);

  height = parseInt(height);

  var codes = stringToCode128(text);

  var g = new Graphics(ctx, width, height);

  var barWeight = g.area.width / ((codes.length - 3) * 11 + 35);

  var x = g.area.left;
  var y = g.area.top;
  for (var i = 0; i < codes.length; i++) {
    var c = codes[i];
    //two bars at a time: 1 black and 1 white
    for (var bar = 0; bar < 8; bar += 2) {
      var barW = PATTERNS[c][bar] * barWeight;
      // var barH = height - y - this.border;
      var barH = height - y;
      var spcW = PATTERNS[c][bar + 1] * barWeight;

      //no need to draw if 0 width
      if (barW > 0) {
        g.fillFgRect(x, y, barW, barH);
      }

      x += barW + spcW;
    }
  }

  // ctx.draw();---------------------------------------------
}


function stringToCode128(text) {

  var barc = {
    currcs: CODESET.C
  };

  var bytes = getBytes(text);
  //decide starting codeset
  var index = bytes[0] == CHAR_TILDE ? 1 : 0;

  var csa1 = bytes.length > 0 ? codeSetAllowedFor(bytes[index++]) : CODESET.AB;
  var csa2 = bytes.length > 0 ? codeSetAllowedFor(bytes[index++]) : CODESET.AB;
  barc.currcs = getBestStartSet(csa1, csa2);
  barc.currcs = perhapsCodeC(bytes, barc.currcs);

  //if no codeset changes this will end up with bytes.length+3
  //start, checksum and stop
  var codes = new Array();

  switch (barc.currcs) {
    case CODESET.A:
      codes.push(SET_STARTA);
      break;
    case CODESET.B:
      codes.push(SET_STARTB);
      break;
    default:
      codes.push(SET_STARTC);
      break;
  }


  for (var i = 0; i < bytes.length; i++) {
    var b1 = bytes[i]; //get the first of a pair
    //should we translate/replace
    if (b1 in REPLACE_CODES) {
      codes.push(REPLACE_CODES[b1]);
      i++ //jump to next
      b1 = bytes[i];
    }

    //get the next in the pair if possible
    var b2 = bytes.length > (i + 1) ? bytes[i + 1] : -1;

    codes = codes.concat(codesForChar(b1, b2, barc.currcs));
    //code C takes 2 chars each time
    if (barc.currcs == CODESET.C) i++;
  }

  //calculate checksum according to Code 128 standards
  var checksum = codes[0];
  for (var weight = 1; weight < codes.length; weight++) {
    checksum += (weight * codes[weight]);
  }
  codes.push(checksum % 103);

  codes.push(SET_STOP);

  //encoding should now be complete
  return codes;

  function getBestStartSet(csa1, csa2) {
    //tries to figure out the best codeset
    //to start with to get the most compact code
    var vote = 0;
    vote += csa1 == CODESET.A ? 1 : 0;
    vote += csa1 == CODESET.B ? -1 : 0;
    vote += csa2 == CODESET.A ? 1 : 0;
    vote += csa2 == CODESET.B ? -1 : 0;
    //tie goes to B due to my own predudices
    return vote > 0 ? CODESET.A : CODESET.B;
  }

  function perhapsCodeC(bytes, codeset) {
    for (var i = 0; i < bytes.length; i++) {
      var b = bytes[i]
      if ((b < 48 || b > 57) && b != CHAR_TILDE)
        return codeset;
    }
    return CODESET.C;
  }

  //chr1 is current byte
  //chr2 is the next byte to process. looks ahead.
  function codesForChar(chr1, chr2, currcs) {
    var result = [];
    var shifter = -1;

    if (charCompatible(chr1, currcs)) {
      if (currcs == CODESET.C) {
        if (chr2 == -1) {
          shifter = SET_CODEB;
          currcs = CODESET.B;
        }
        else if ((chr2 != -1) && !charCompatible(chr2, currcs)) {
          //need to check ahead as well
          if (charCompatible(chr2, CODESET.A)) {
            shifter = SET_CODEA;
            currcs = CODESET.A;
          }
          else {
            shifter = SET_CODEB;
            currcs = CODESET.B;
          }
        }
      }
    }
    else {
      //if there is a next char AND that next char is also not compatible
      if ((chr2 != -1) && !charCompatible(chr2, currcs)) {
        //need to switch code sets
        switch (currcs) {
          case CODESET.A:
            shifter = SET_CODEB;
            currcs = CODESET.B;
            break;
          case CODESET.B:
            shifter = SET_CODEA;
            currcs = CODESET.A;
            break;
        }
      }
      else {
        //no need to shift code sets, a temporary SHIFT will suffice
        shifter = SET_SHIFT;
      }
    }

    //ok some type of shift is nessecary
    if (shifter != -1) {
      result.push(shifter);
      // result.push(codeValue(chr2));-----------------------------------
      result.push(codeValue(chr1));
    }
    else {
      if (currcs == CODESET.C) {
        //include next as well
        result.push(codeValue(chr1, chr2));
      }
      else {
        result.push(codeValue(chr1));
      }
    }
    barc.currcs = currcs;

    return result;
  }
}

//reduce the ascii code to fit into the Code128 char table
function codeValue(chr1, chr2) {
  if (typeof chr2 == "undefined") {
    return chr1 >= 32 ? chr1 - 32 : chr1 + 64;
  }
  else {
    return parseInt(String.fromCharCode(chr1) + String.fromCharCode(chr2));
  }
}

function charCompatible(chr, codeset) {
  var csa = codeSetAllowedFor(chr);
  if (csa == CODESET.ANY) return true;
  //if we need to change from current
  if (csa == CODESET.AB) return true;
  if (csa == CODESET.A && codeset == CODESET.A) return true;
  if (csa == CODESET.B && codeset == CODESET.B) return true;
  return false;
}

function codeSetAllowedFor(chr) {
  if (chr >= 48 && chr <= 57) {
    //0-9
    return CODESET.ANY;
  }
  else if (chr >= 32 && chr <= 95) {
    //0-9 A-Z
    return CODESET.AB;
  }
  else {
    //if non printable
    return chr < 32 ? CODESET.A : CODESET.B;
  }
}

var Graphics = function (ctx, width, height) {

  this.width = width;
  this.height = height;
  this.quiet = Math.round(this.width / 40);

  this.border_size = 0;
  this.padding_width = 0;

  this.area = {
    width: width - this.padding_width * 2 - this.quiet * 2,
    height: height - this.border_size * 2,
    top: this.border_size - 4,
    left: this.padding_width + this.quiet
  };

  this.ctx = ctx;
  this.fg = "#000000";
  this.bg = "#ffffff";

  // fill background
  this.fillBgRect(0, 0, width, height);

  // fill center to create border
  this.fillBgRect(0, this.border_size, width, height - this.border_size * 2);
}

//use native color
Graphics.prototype._fillRect = function (x, y, width, height, color) {
  // this.ctx.setFillStyle(color)---------------------------------
  this.ctx.fillStyle  = color
  this.ctx.fillRect(x, y, width, height)
}

Graphics.prototype.fillFgRect = function (x, y, width, height) {
  this._fillRect(x, y, width, height, this.fg);
}

Graphics.prototype.fillBgRect = function (x, y, width, height) {
  this._fillRect(x, y, width, height, this.bg);
}

var PATTERNS = [
  [2, 1, 2, 2, 2, 2, 0, 0],  // 0
  [2, 2, 2, 1, 2, 2, 0, 0],  // 1
  [2, 2, 2, 2, 2, 1, 0, 0],  // 2
  [1, 2, 1, 2, 2, 3, 0, 0],  // 3
  [1, 2, 1, 3, 2, 2, 0, 0],  // 4
  [1, 3, 1, 2, 2, 2, 0, 0],  // 5
  [1, 2, 2, 2, 1, 3, 0, 0],  // 6
  [1, 2, 2, 3, 1, 2, 0, 0],  // 7
  [1, 3, 2, 2, 1, 2, 0, 0],  // 8
  [2, 2, 1, 2, 1, 3, 0, 0],  // 9
  [2, 2, 1, 3, 1, 2, 0, 0],  // 10
  [2, 3, 1, 2, 1, 2, 0, 0],  // 11
  [1, 1, 2, 2, 3, 2, 0, 0],  // 12
  [1, 2, 2, 1, 3, 2, 0, 0],  // 13
  [1, 2, 2, 2, 3, 1, 0, 0],  // 14
  [1, 1, 3, 2, 2, 2, 0, 0],  // 15
  [1, 2, 3, 1, 2, 2, 0, 0],  // 16
  [1, 2, 3, 2, 2, 1, 0, 0],  // 17
  [2, 2, 3, 2, 1, 1, 0, 0],  // 18
  [2, 2, 1, 1, 3, 2, 0, 0],  // 19
  [2, 2, 1, 2, 3, 1, 0, 0],  // 20
  [2, 1, 3, 2, 1, 2, 0, 0],  // 21
  [2, 2, 3, 1, 1, 2, 0, 0],  // 22
  [3, 1, 2, 1, 3, 1, 0, 0],  // 23
  [3, 1, 1, 2, 2, 2, 0, 0],  // 24
  [3, 2, 1, 1, 2, 2, 0, 0],  // 25
  [3, 2, 1, 2, 2, 1, 0, 0],  // 26
  [3, 1, 2, 2, 1, 2, 0, 0],  // 27
  [3, 2, 2, 1, 1, 2, 0, 0],  // 28
  [3, 2, 2, 2, 1, 1, 0, 0],  // 29
  [2, 1, 2, 1, 2, 3, 0, 0],  // 30
  [2, 1, 2, 3, 2, 1, 0, 0],  // 31
  [2, 3, 2, 1, 2, 1, 0, 0],  // 32
  [1, 1, 1, 3, 2, 3, 0, 0],  // 33
  [1, 3, 1, 1, 2, 3, 0, 0],  // 34
  [1, 3, 1, 3, 2, 1, 0, 0],  // 35
  [1, 1, 2, 3, 1, 3, 0, 0],  // 36
  [1, 3, 2, 1, 1, 3, 0, 0],  // 37
  [1, 3, 2, 3, 1, 1, 0, 0],  // 38
  [2, 1, 1, 3, 1, 3, 0, 0],  // 39
  [2, 3, 1, 1, 1, 3, 0, 0],  // 40
  [2, 3, 1, 3, 1, 1, 0, 0],  // 41
  [1, 1, 2, 1, 3, 3, 0, 0],  // 42
  [1, 1, 2, 3, 3, 1, 0, 0],  // 43
  [1, 3, 2, 1, 3, 1, 0, 0],  // 44
  [1, 1, 3, 1, 2, 3, 0, 0],  // 45
  [1, 1, 3, 3, 2, 1, 0, 0],  // 46
  [1, 3, 3, 1, 2, 1, 0, 0],  // 47
  [3, 1, 3, 1, 2, 1, 0, 0],  // 48
  [2, 1, 1, 3, 3, 1, 0, 0],  // 49
  [2, 3, 1, 1, 3, 1, 0, 0],  // 50
  [2, 1, 3, 1, 1, 3, 0, 0],  // 51
  [2, 1, 3, 3, 1, 1, 0, 0],  // 52
  [2, 1, 3, 1, 3, 1, 0, 0],  // 53
  [3, 1, 1, 1, 2, 3, 0, 0],  // 54
  [3, 1, 1, 3, 2, 1, 0, 0],  // 55
  [3, 3, 1, 1, 2, 1, 0, 0],  // 56
  [3, 1, 2, 1, 1, 3, 0, 0],  // 57
  [3, 1, 2, 3, 1, 1, 0, 0],  // 58
  [3, 3, 2, 1, 1, 1, 0, 0],  // 59
  [3, 1, 4, 1, 1, 1, 0, 0],  // 60
  [2, 2, 1, 4, 1, 1, 0, 0],  // 61
  [4, 3, 1, 1, 1, 1, 0, 0],  // 62
  [1, 1, 1, 2, 2, 4, 0, 0],  // 63
  [1, 1, 1, 4, 2, 2, 0, 0],  // 64
  [1, 2, 1, 1, 2, 4, 0, 0],  // 65
  [1, 2, 1, 4, 2, 1, 0, 0],  // 66
  [1, 4, 1, 1, 2, 2, 0, 0],  // 67
  [1, 4, 1, 2, 2, 1, 0, 0],  // 68
  [1, 1, 2, 2, 1, 4, 0, 0],  // 69
  [1, 1, 2, 4, 1, 2, 0, 0],  // 70
  [1, 2, 2, 1, 1, 4, 0, 0],  // 71
  [1, 2, 2, 4, 1, 1, 0, 0],  // 72
  [1, 4, 2, 1, 1, 2, 0, 0],  // 73
  [1, 4, 2, 2, 1, 1, 0, 0],  // 74
  [2, 4, 1, 2, 1, 1, 0, 0],  // 75
  [2, 2, 1, 1, 1, 4, 0, 0],  // 76
  [4, 1, 3, 1, 1, 1, 0, 0],  // 77
  [2, 4, 1, 1, 1, 2, 0, 0],  // 78
  [1, 3, 4, 1, 1, 1, 0, 0],  // 79
  [1, 1, 1, 2, 4, 2, 0, 0],  // 80
  [1, 2, 1, 1, 4, 2, 0, 0],  // 81
  [1, 2, 1, 2, 4, 1, 0, 0],  // 82
  [1, 1, 4, 2, 1, 2, 0, 0],  // 83
  [1, 2, 4, 1, 1, 2, 0, 0],  // 84
  [1, 2, 4, 2, 1, 1, 0, 0],  // 85
  [4, 1, 1, 2, 1, 2, 0, 0],  // 86
  [4, 2, 1, 1, 1, 2, 0, 0],  // 87
  [4, 2, 1, 2, 1, 1, 0, 0],  // 88
  [2, 1, 2, 1, 4, 1, 0, 0],  // 89
  [2, 1, 4, 1, 2, 1, 0, 0],  // 90
  [4, 1, 2, 1, 2, 1, 0, 0],  // 91
  [1, 1, 1, 1, 4, 3, 0, 0],  // 92
  [1, 1, 1, 3, 4, 1, 0, 0],  // 93
  [1, 3, 1, 1, 4, 1, 0, 0],  // 94
  [1, 1, 4, 1, 1, 3, 0, 0],  // 95
  [1, 1, 4, 3, 1, 1, 0, 0],  // 96
  [4, 1, 1, 1, 1, 3, 0, 0],  // 97
  [4, 1, 1, 3, 1, 1, 0, 0],  // 98
  [1, 1, 3, 1, 4, 1, 0, 0],  // 99
  [1, 1, 4, 1, 3, 1, 0, 0],  // 100
  [3, 1, 1, 1, 4, 1, 0, 0],  // 101
  [4, 1, 1, 1, 3, 1, 0, 0],  // 102
  [2, 1, 1, 4, 1, 2, 0, 0],  // 103
  [2, 1, 1, 2, 1, 4, 0, 0],  // 104
  [2, 1, 1, 2, 3, 2, 0, 0],  // 105
  [2, 3, 3, 1, 1, 1, 2, 0]   // 106
]
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2. utils下新增codeIndex.js文件

var barcode = require('./barCode');

function convert_length(length) {
    return Math.round(wx.getSystemInfoSync().windowWidth * length / 750);
}

function barc(context, code, width, height) {
  barcode.code128(context, code, convert_length(width), convert_length(height))
}

function qrc(id, code, width, height) {
    qrcode.api.draw(code, {
        ctx: wx.createCanvasContext(id),
        width: convert_length(width),
        height: convert_length(height)
    })
}

module.exports = {
    barcode: barc,
    qrcode: qrc
}
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3.业务wxml里新增元素

<canvas type="2d" id="barcode"></canvas>
1

4. 业务js里新增方法

  // 创建条形码
  createBarcode: function () {
    const query = wx.createSelectorQuery()
    query.select('#barcode')
      .fields({
        node: true,
        size: true
      })
      .exec((res) => {
        const canvas = res[0].node
        if (!canvas) return
        /* 获取 canvas 实例 */
        const context = canvas.getContext('2d')
        const dpr = wx.getSystemInfoSync().pixelRatio
        canvas.width = res[0].width * dpr
        canvas.height = res[0].height * dpr
        context.scale(dpr, dpr)
        barCode.barcode(context, '123456', 440, 180)
      })
  },
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5. 业务样式

#barcode{
    display: block;
    width: 600rpx;
    height: 140rpx;
    margin: 0 auto;
    position: relative;
    z-index: 1;
 }
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5. 提示：上述1/2的源码是经过处理的，直接用就可以了

这里标注一下都做了什么处理：原来源码是用的 wx.createCanvasContext(id)，这个方法已经被废弃了。处理后改成了 wx.createSelectorQuery()方法，相应的，源码中的其他部分也要发生变化。

1. codeIndex.js

原来的：

function barc(id, code, width, height) {
    barcode.code128(wx.createCanvasContext(id), code, convert_length(width), convert_length(height))
}
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改为：

function barc(ctx, code, width, height) {
    barcode.code128(ctx, code, convert_length(width), convert_length(height))
}
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2.barCode.js

原来的

Graphics.prototype._fillRect = function(x, y, width, height, color) {
    this.ctx.setFillStyle(color)
    this.ctx.fillRect(x, y, width, height)
}
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改为：

Graphics.prototype._fillRect = function(x, y, width, height, color) {
    this.ctx.fillStyle  = color;
    this.ctx.fillRect(x, y, width, height)
}
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3.barCode.js

注掉 ctx.draw()

4.barCode.js

搜索result.push(codeValue(chr2)) 将chr2改为chr1

 if (shifter != -1) {
     result.push(shifter);
     result.push(codeValue(chr1));
 }
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源码： https://www.jianshu.com/p/3abec53a0bb2
处理方法原帖：https://developers.weixin.qq.com/community/develop/article/doc/0006cae8024368f5240fc99b15b813