index.js

'use strict'

module.exports = normalize

var arcToCurve = require('svg-arc-to-cubic-bezier')

function normalize(path){
  // init state
  var prev
  var result = []
  var bezierX = 0
  var bezierY = 0
  var startX = 0
  var startY = 0
  var quadX = null
  var quadY = null
  var x = 0
  var y = 0

  for (var i = 0, len = path.length; i < len; i++) {
    var seg = path[i]
    var command = seg[0]

    switch (command) {
      case 'M':
        startX = seg[1]
        startY = seg[2]
        break
      case 'A':
        var curves = arcToCurve({
          px: x,
          py: y,
          cx: seg[6],
          cy:  seg[7],
          rx: seg[1],
          ry: seg[2],
          xAxisRotation: seg[3],
          largeArcFlag: seg[4],
          sweepFlag: seg[5]
        })

        // null-curves
        if (!curves.length) continue

        for (var j = 0, c; j < curves.length; j++) {
          c = curves[j]
          seg = ['C', c.x1, c.y1, c.x2, c.y2, c.x, c.y]
          if (j < curves.length - 1) result.push(seg)
        }

        break
      case 'S':
        // default control point
        var cx = x
        var cy = y
        if (prev == 'C' || prev == 'S') {
          cx += cx - bezierX // reflect the previous command's control
          cy += cy - bezierY // point relative to the current point
        }
        seg = ['C', cx, cy, seg[1], seg[2], seg[3], seg[4]]
        break
      case 'T':
        if (prev == 'Q' || prev == 'T') {
          quadX = x * 2 - quadX // as with 'S' reflect previous control point
          quadY = y * 2 - quadY
        } else {
          quadX = x
          quadY = y
        }
        seg = quadratic(x, y, quadX, quadY, seg[1], seg[2])
        break
      case 'Q':
        quadX = seg[1]
        quadY = seg[2]
        seg = quadratic(x, y, seg[1], seg[2], seg[3], seg[4])
        break
      case 'L':
        seg = line(x, y, seg[1], seg[2])
        break
      case 'H':
        seg = line(x, y, seg[1], y)
        break
      case 'V':
        seg = line(x, y, x, seg[1])
        break
      case 'Z':
        seg = line(x, y, startX, startY)
        break
    }

    // update state
    prev = command
    x = seg[seg.length - 2]
    y = seg[seg.length - 1]
    if (seg.length > 4) {
      bezierX = seg[seg.length - 4]
      bezierY = seg[seg.length - 3]
    } else {
      bezierX = x
      bezierY = y
    }
    result.push(seg)
  }

  return result
}

function line(x1, y1, x2, y2){
  return ['C', x1, y1, x2, y2, x2, y2]
}

function quadratic(x1, y1, cx, cy, x2, y2){
  return [
    'C',
    x1/3 + (2/3) * cx,
    y1/3 + (2/3) * cy,
    x2/3 + (2/3) * cx,
    y2/3 + (2/3) * cy,
    x2,
    y2
  ]
}