# All files filter-pack.js

95.83% Statements 92/96
81.82% Branches 36/44
100% Functions 11/11
95.24% Lines 80/84

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     "use strict";

    let paethPredictor = require("./paeth-predictor");

    function filterNone(pxData, pxPos, byteWidth, rawData, rawPos) {
      for (let x = 0; x < byteWidth; x++) {
        rawData[rawPos + x] = pxData[pxPos + x];
      }
    }

    function filterSumNone(pxData, pxPos, byteWidth) {
      let sum = 0;
      let length = pxPos + byteWidth;

      for (let i = pxPos; i < length; i++) {
        sum += Math.abs(pxData[i]);
      }
      return sum;
    }

    function filterSub(pxData, pxPos, byteWidth, rawData, rawPos, bpp) {
      for (let x = 0; x < byteWidth; x++) {
        let left = x >= bpp ? pxData[pxPos + x - bpp] : 0;
        let val = pxData[pxPos + x] - left;

        rawData[rawPos + x] = val;
      }
    }

    function filterSumSub(pxData, pxPos, byteWidth, bpp) {
      let sum = 0;
      for (let x = 0; x < byteWidth; x++) {
        let left = x >= bpp ? pxData[pxPos + x - bpp] : 0;
        let val = pxData[pxPos + x] - left;

        sum += Math.abs(val);
      }

      return sum;
    }

    function filterUp(pxData, pxPos, byteWidth, rawData, rawPos) {
      for (let x = 0; x < byteWidth; x++) {
        let up = pxPos > 0 ? pxData[pxPos + x - byteWidth] : 0;
        let val = pxData[pxPos + x] - up;

        rawData[rawPos + x] = val;
      }
    }

    function filterSumUp(pxData, pxPos, byteWidth) {
      let sum = 0;
      let length = pxPos + byteWidth;
      for (let x = pxPos; x < length; x++) {
        let up = pxPos > 0 ? pxData[x - byteWidth] : 0;
        let val = pxData[x] - up;

        sum += Math.abs(val);
      }

      return sum;
    }

    function filterAvg(pxData, pxPos, byteWidth, rawData, rawPos, bpp) {
      for (let x = 0; x < byteWidth; x++) {
        let left = x >= bpp ? pxData[pxPos + x - bpp] : 0;
        let up = pxPos > 0 ? pxData[pxPos + x - byteWidth] : 0;
        let val = pxData[pxPos + x] - ((left + up) >> 1);

        rawData[rawPos + x] = val;
      }
    }

    function filterSumAvg(pxData, pxPos, byteWidth, bpp) {
      let sum = 0;
      for (let x = 0; x < byteWidth; x++) {
        let left = x >= bpp ? pxData[pxPos + x - bpp] : 0;
        let up = pxPos > 0 ? pxData[pxPos + x - byteWidth] : 0;
        let val = pxData[pxPos + x] - ((left + up) >> 1);

        sum += Math.abs(val);
      }

      return sum;
    }

    function filterPaeth(pxData, pxPos, byteWidth, rawData, rawPos, bpp) {
      for (let x = 0; x < byteWidth; x++) {
        let left = x >= bpp ? pxData[pxPos + x - bpp] : 0;
        let up = pxPos > 0 ? pxData[pxPos + x - byteWidth] : 0;
        let upleft =
          pxPos > 0 && x >= bpp ? pxData[pxPos + x - (byteWidth + bpp)] : 0;
        let val = pxData[pxPos + x] - paethPredictor(left, up, upleft);

        rawData[rawPos + x] = val;
      }
    }

    function filterSumPaeth(pxData, pxPos, byteWidth, bpp) {
      let sum = 0;
      for (let x = 0; x < byteWidth; x++) {
        let left = x >= bpp ? pxData[pxPos + x - bpp] : 0;
        let up = pxPos > 0 ? pxData[pxPos + x - byteWidth] : 0;
        let upleft =
          pxPos > 0 && x >= bpp ? pxData[pxPos + x - (byteWidth + bpp)] : 0;
        let val = pxData[pxPos + x] - paethPredictor(left, up, upleft);

        sum += Math.abs(val);
      }

      return sum;
    }

    let filters = {
      0: filterNone,
      1: filterSub,
      2: filterUp,
      3: filterAvg,
      4: filterPaeth,
    };

    let filterSums = {
      0: filterSumNone,
      1: filterSumSub,
      2: filterSumUp,
      3: filterSumAvg,
      4: filterSumPaeth,
    };

    module.exports = function (pxData, width, height, options, bpp) {
      let filterTypes;
      Eif (!("filterType" in options) || options.filterType === -1) {
        filterTypes = [0, 1, 2, 3, 4];
      } else if (typeof options.filterType === "number") {
        filterTypes = [options.filterType];
      } else {
        throw new Error("unrecognised filter types");
      }

      Iif (options.bitDepth === 16) {
        bpp *= 2;
      }
      let byteWidth = width * bpp;
      let rawPos = 0;
      let pxPos = 0;
      let rawData = Buffer.alloc((byteWidth + 1) * height);

      let sel = filterTypes[0];

      for (let y = 0; y < height; y++) {
        Eif (filterTypes.length > 1) {
          // find best filter for this line (with lowest sum of values)
          let min = Infinity;

          for (let i = 0; i < filterTypes.length; i++) {
            let sum = filterSums[filterTypes[i]](pxData, pxPos, byteWidth, bpp);
            if (sum < min) {
              sel = filterTypes[i];
              min = sum;
            }
          }
        }

        rawData[rawPos] = sel;
        rawPos++;
        filters[sel](pxData, pxPos, byteWidth, rawData, rawPos, bpp);
        rawPos += byteWidth;
        pxPos += byteWidth;
      }
      return rawData;
    };