Function getTextureChannel

lib/loadMtl.js:425–467

(
  texture,
  index,
  targetWidth,
  targetHeight,
  targetChannel,
)

let scratchResizeChannel;

function getTextureChannel(
  texture,
  index,
  targetWidth,
  targetHeight,
  targetChannel,
) {
  const pixels = texture.pixels; // RGBA
  const sourceWidth = texture.width;
  const sourceHeight = texture.height;
  const sourcePixelsLength = sourceWidth * sourceHeight;
  const targetPixelsLength = targetWidth * targetHeight;

  // Allocate the scratchResizeChannel on demand if the texture needs to be resized
  let sourceChannel = targetChannel;
  if (sourcePixelsLength > targetPixelsLength) {
    if (
      !defined(scratchResizeChannel) ||
      sourcePixelsLength > scratchResizeChannel.length
    ) {
      scratchResizeChannel = Buffer.alloc(sourcePixelsLength);
    }
    sourceChannel = scratchResizeChannel;
  }

  for (let i = 0; i < sourcePixelsLength; ++i) {
    const value = pixels.readUInt8(i * 4 + index);
    sourceChannel.writeUInt8(value, i);
  }

  if (sourcePixelsLength > targetPixelsLength) {
    resizeChannel(
      sourceChannel,
      sourceWidth,
      sourceHeight,
      targetChannel,
      targetWidth,
      targetHeight,
    );
  }

  return targetChannel;
}

function writeChannel(pixels, channel, index) {
  const pixelsLength = pixels.length / 4;