static scaleTextureDown()

in src/engine/loaders/voltools.js [286:345]
54 lines of code
13 McCabe index (conditional complexity)

  static scaleTextureDown(loader, pixelsSrc, xDimDst, yDimDst, zDimDst) {
    const ACC_BITS = 10;
    const ACC_HALF = 1 << (ACC_BITS - 1);
    const xyzDimDst = xDimDst * yDimDst * zDimDst;
    const pixelsDst = new Uint8Array(xyzDimDst);

    const xDimSrc = loader.m_xDim;
    const yDimSrc = loader.m_yDim;
    const zDimSrc = loader.m_zDim;

    const isCorrectDim = xDimSrc > xDimDst || yDimSrc > yDimDst || zDimSrc > zDimDst;
    if (!isCorrectDim) {
      return null;
    }
    const xyDimSrc = xDimSrc * yDimSrc;

    const xStep = Math.floor((xDimSrc << ACC_BITS) / xDimDst);
    const yStep = Math.floor((yDimSrc << ACC_BITS) / yDimDst);
    const zStep = Math.floor((zDimSrc << ACC_BITS) / zDimDst);
    let indDst = 0;
    let zSrcAccL = ACC_HALF;
    let zSrcAccH = zSrcAccL + zStep;
    for (let zDst = 0; zDst < zDimDst; zDst++, zSrcAccL += zStep, zSrcAccH += zStep) {
      const zSrcL = zSrcAccL >> ACC_BITS;
      const zSrcH = zSrcAccH >> ACC_BITS;

      let ySrcAccL = ACC_HALF;
      let ySrcAccH = ySrcAccL + yStep;
      for (let yDst = 0; yDst < yDimDst; yDst++, ySrcAccL += yStep, ySrcAccH += yStep) {
        const ySrcL = ySrcAccL >> ACC_BITS;
        const ySrcH = ySrcAccH >> ACC_BITS;

        let xSrcAccL = ACC_HALF;
        let xSrcAccH = xSrcAccL + xStep;
        for (let xDst = 0; xDst < xDimDst; xDst++, xSrcAccL += xStep, xSrcAccH += xStep) {
          const xSrcL = xSrcAccL >> ACC_BITS;
          const xSrcH = xSrcAccH >> ACC_BITS;

          // Accumulate sum
          let sum = 0;
          let numPixels = 0;
          for (let z = zSrcL, zOff = zSrcL * xyDimSrc; z < zSrcH; z++, zOff += xyDimSrc) {
            for (let y = ySrcL, yOff = ySrcL * xDimSrc; y < ySrcH; y++, yOff += xDimSrc) {
              for (let x = xSrcL; x < xSrcH; x++) {
                const offSrc = x + yOff + zOff;
                sum += pixelsSrc[offSrc];
                numPixels++;
              } // for (x)
            } // for (y)
          } // for (z)
          sum = Math.floor(sum / numPixels);
          pixelsDst[indDst++] = sum;
        } // for (xDst)
      } // for (yDst)
    } // for (zDst)
    loader.m_xDim = xDimDst;
    loader.m_yDim = yDimDst;
    loader.m_zDim = zDimDst;
    return pixelsDst;
  } // end of scaleTextureDown