All files / packages/core/src/RenderingEngine/helpers/cpuFallback/rendering storedPixelDataToCanvasImageDataPET.ts

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import now from './now';
import { IImage } from '../../../../types';
 
/**
 * This function transforms stored pixel values into a canvas image data buffer
 * by using a LUT.  This is the most performance sensitive code in cornerstone and
 * we use a special trick to make this go as fast as possible.  Specifically we
 * use the alpha channel only to control the luminance rather than the red, green and
 * blue channels which makes it over 3x faster. The canvasImageDataData buffer needs
 * to be previously filled with white pixels.
 *
 * NOTE: Attribution would be appreciated if you use this technique!
 *
 * @param {Image} image A Cornerstone Image Object
 * @param {Array} lut Lookup table array
 * @param {Uint8ClampedArray} canvasImageDataData canvasImageData.data buffer filled with white pixels
 *
 * @returns {void}
 * @memberof Internal
 */
export default function (
  image: IImage,
  lutFunction: (value: number) => number,
  canvasImageDataData: Uint8ClampedArray
): void {
  let start = now();
  const pixelData = image.getPixelData();
 
  image.stats.lastGetPixelDataTime = now() - start;
 
  const numPixels = pixelData.length;
  // const minPixelValue = image.minPixelValue;
  let canvasImageDataIndex = 3;
  let storedPixelDataIndex = 0;
 
  // NOTE: As of Nov 2014, most javascript engines have lower performance when indexing negative indexes.
  // We have a special code path for this case that improves performance.  Thanks to @jpambrun for this enhancement
 
  // Added two paths (Int16Array, Uint16Array) to avoid polymorphic deoptimization in chrome.
  start = now();
 
  while (storedPixelDataIndex < numPixels) {
    canvasImageDataData[canvasImageDataIndex] = lutFunction(
      pixelData[storedPixelDataIndex++]
    ); // Alpha
    canvasImageDataIndex += 4;
  }
 
  image.stats.lastStoredPixelDataToCanvasImageDataTime = now() - start;
}