squoosh/src/codecs/rotate/processor.ts

import wasmUrl from '../../../codecs/rotate/rotate.wasm';
import { RotateOptions, RotateModuleInstance } from './processor-meta';

const instancePromise = (WebAssembly as any).instantiateStreaming(fetch(wasmUrl));

export async function rotate(
  data: ImageData,
  opts: RotateOptions,
): Promise<ImageData> {
  const { instance } = (await instancePromise) as {instance: RotateModuleInstance};

  // Number of wasm memory pages (á 64KiB) needed to store the image twice.
  const bytesPerImage = data.width * data.height * 4;
  const numPagesNeeded = Math.ceil((bytesPerImage * 2 + 4) / (64 * 1024));
  // Only count full pages, just to be safe.
  const numPagesAvailable = Math.floor(instance.exports.memory.buffer.byteLength / (64 * 1024));
  const additionalPagesToAllocate = numPagesNeeded - numPagesAvailable;

  if (additionalPagesToAllocate > 0) {
    instance.exports.memory.grow(additionalPagesToAllocate);
  }
  const view = new Uint8ClampedArray(instance.exports.memory.buffer);
  view.set(data.data, 4);

  instance.exports.rotate(data.width, data.height, opts.rotate);

  const flipDimensions = opts.rotate % 180 !== 0;
  return new ImageData(
    view.slice(bytesPerImage + 4, bytesPerImage * 2 + 4),
    flipDimensions ? data.height : data.width,
    flipDimensions ? data.width : data.height,
  );
}