ccv_pre.js

// Helpers used in the C++ bindings

Module = Module || {};

Module.isImageData = function(element) {
  return element instanceof ImageData;
};

Module.isCanvasImageSource = function(element) {
  return (
    element instanceof HTMLCanvasElement ||
    element instanceof HTMLImageElement ||
    element instanceof HTMLVideoElement ||
    element instanceof ImageBitmap
  );
};

Module.toCanvas = function(source) {
  console.assert(Module.isCanvasImageSource(source));
  if (source instanceof HTMLCanvasElement) {
    return source;
  }
  var canvas = document.createElement('canvas'); // draw to a temp canvas
  canvas.width = source.videoWidth || source.naturalWidth || source.width;
  canvas.height =  source.videoHeight || source.naturalHeight || source.height;
  canvas.getContext('2d').drawImage(source, 0, 0, canvas.width, canvas.height);
  return canvas;
};

// Reads image data from ImageData or CanvasImageSource(HTMLCanvasElement or HTMLImageElement or HTMLVideoElement or ImageBitmap)
// TODO: maybe CanvasRenderingContext2D and Blob also?
Module.readImageData = function(source) {
  console.assert(source);
  if (Module.isImageData(source)) {
    return source;
  }
  var canvas = Module.toCanvas(source);
  return canvas.getContext('2d').getImageData(0, 0, canvas.width, canvas.height);
};

Module.writeImageDataToCanvas = function(canvas, data, width, height) {
  canvas.width = width;
  canvas.height = height;
  var context = canvas.getContext('2d');
  var imageData = context.createImageData(width, height);
  imageData.data.set(data);
  context.putImageData(imageData, 0, 0);
  return canvas;
};

// Writes image data into ImageData, HTMLCanvasElement, HTMLImageElement or creates a new canvas and appends it
Module.writeImageData = function(dest, data, width, height) {
  console.assert(dest);

  if (typeof dest === 'function') {
    dest(data, width, height);
    return;
  }

  if (Module.isImageData(dest)) {
    console.assert(dest.width === width, dest.height === height);
    dest.data.set(data);
    return;
  }

  console.assert(dest instanceof HTMLElement);
  console.assert(!(dest instanceof HTMLVideoElement), 'Cannot write to video element');
  var canvas = (dest instanceof HTMLCanvasElement) ? dest : document.createElement('canvas');
  Module.writeImageDataToCanvas(canvas, data, width, height);

  if (!(dest instanceof HTMLCanvasElement)) {
    if (dest instanceof HTMLImageElement) {
      dest.src = canvas.toDataURL();
    } else {
      dest.appendChild(canvas);
    }
  }
};