Function pickObjectsFromPixels

packages/engine/Source/Scene/PickFramebuffer.js:45–99

* Return the picked object(s) rendered within a given rectangle. * * @private * @param {object} context The active context. * @param {Uint8Array|Uint16Array|Float32Array|Uint32Array} pixels The pixels in the specified rectangle. * @param {number} width The rectangle width. * @param {number} he

(context, pixels, width, height, limit = 1)

 * @returns {object[]} A list of rendered objects, ordered by distance to the middle of the rectangle.
 */
function pickObjectsFromPixels(context, pixels, width, height, limit = 1) {
  const max = Math.max(width, height);
  const length = max * max;
  const halfWidth = Math.floor(width * 0.5);
  const halfHeight = Math.floor(height * 0.5);

  let x = 0;
  let y = 0;
  let dx = 0;
  let dy = -1;

  // Spiral around the center pixel, this is a workaround until
  // we can access the depth buffer on all browsers.

  // The region does not have to square and the dimensions do not have to be odd, but
  // loop iterations would be wasted. Prefer square regions where the size is odd.
  const objects = new Set();
  for (let i = 0; i < length; ++i) {
    if (
      -halfWidth <= x &&
      x <= halfWidth &&
      -halfHeight <= y &&
      y <= halfHeight
    ) {
      const index = 4 * ((halfHeight - y) * width + x + halfWidth);

      const pickColor = Color.bytesToRgba(
        pixels[index],
        pixels[index + 1],
        pixels[index + 2],
        pixels[index + 3],
      );

      const object = context.getObjectByPickColor(pickColor);
      if (defined(object)) {
        objects.add(object);
        if (objects.size >= limit) {
          break;
        }
      }
    }

    // if (top right || bottom left corners) || (top left corner) || (bottom right corner + (1, 0))
    // change spiral direction
    if (x === y || (x < 0 && -x === y) || (x > 0 && x === 1 - y)) {
      const temp = dx;
      dx = -dy;
      dy = temp;
    }

    x += dx;
    y += dy;
  }
  return [...objects];
}

PickFramebuffer.prototype.begin = function (screenSpaceRectangle, viewport) {
  const context = this._context;