Function _flipPixels

src/image/loading_displaying.js:527–553

(pixels, width, height)

  };

  function _flipPixels(pixels, width, height) {
    // extracting the pixels using readPixels returns
    // an upside down image. we have to flip it back
    // first. this solution is proposed by gman on
    // this stack overflow answer:
    // https://stackoverflow.com/questions/41969562/how-can-i-flip-the-result-of-webglrenderingcontext-readpixels

    const halfHeight = parseInt(height / 2);
    const bytesPerRow = width * 4;

    // make a temp buffer to hold one row
    const temp = new Uint8Array(width * 4);
    for (let y = 0; y < halfHeight; ++y) {
      const topOffset = y * bytesPerRow;
      const bottomOffset = (height - y - 1) * bytesPerRow;

      // make copy of a row on the top half
      temp.set(pixels.subarray(topOffset, topOffset + bytesPerRow));

      // copy a row from the bottom half to the top
      pixels.copyWithin(topOffset, bottomOffset, bottomOffset + bytesPerRow);

      // copy the copy of the top half row to the bottom half
      pixels.set(temp, bottomOffset);
    }
    return pixels;
  }

  function _generateGlobalPalette(frames) {
    // make an array the size of every possible color in every possible frame