/**
 * This module contains a function to convert stored pixel values to display pixel values using a LUT
 */
var cornerstone = (function (cornerstone) {

    "use strict";

    if(cornerstone === undefined) {
        cornerstone = {};
    }

    /**
     * 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 pixelData the pixel data
     * @param lut the lut
     * @param canvasImageDataData a canvasImgageData.data buffer filled with white pixels
     */
    function storedPixelDataToCanvasImageData(image, lut, canvasImageDataData)
    {
        var pixelData = image.getPixelData();
        var minPixelValue = image.minPixelValue;
        var canvasImageDataIndex = 3;
        var storedPixelDataIndex = 0;
        var localNumPixels = pixelData.length;
        var localPixelData = pixelData;
        var localLut = lut;
        var localCanvasImageDataData = canvasImageDataData;
        // 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
        if(minPixelValue < 0){
            while(storedPixelDataIndex < localNumPixels) {
                localCanvasImageDataData[canvasImageDataIndex] = localLut[localPixelData[storedPixelDataIndex++] + (-minPixelValue)]; // alpha
                canvasImageDataIndex += 4;
            }
        }else{
            while(storedPixelDataIndex < localNumPixels) {
                localCanvasImageDataData[canvasImageDataIndex] = localLut[localPixelData[storedPixelDataIndex++]]; // alpha
                canvasImageDataIndex += 4;
            }
        }
    }

    function storedColorPixelDataToCanvasImageData(image, lut, canvasImageDataData)
    {
        var minPixelValue = image.minPixelValue;
        var canvasImageDataIndex = 0;
        var storedPixelDataIndex = 0;
        var numPixels = image.width * image.height * 4;
        var storedPixelData = image.getPixelData();
        var localLut = lut;
        var localCanvasImageDataData = canvasImageDataData;
        // 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
        if(minPixelValue < 0){
            while(storedPixelDataIndex < numPixels) {
                localCanvasImageDataData[canvasImageDataIndex++] = localLut[storedPixelData[storedPixelDataIndex++] + (-minPixelValue)]; // red
                localCanvasImageDataData[canvasImageDataIndex++] = localLut[storedPixelData[storedPixelDataIndex++] + (-minPixelValue)]; // green
                localCanvasImageDataData[canvasImageDataIndex] = localLut[storedPixelData[storedPixelDataIndex] + (-minPixelValue)]; // blue
                storedPixelDataIndex+=2;
                canvasImageDataIndex+=2;
            }
        }else{
            while(storedPixelDataIndex < numPixels) {
                localCanvasImageDataData[canvasImageDataIndex++] = localLut[storedPixelData[storedPixelDataIndex++]]; // red
                localCanvasImageDataData[canvasImageDataIndex++] = localLut[storedPixelData[storedPixelDataIndex++]]; // green
                localCanvasImageDataData[canvasImageDataIndex] = localLut[storedPixelData[storedPixelDataIndex]]; // blue
                storedPixelDataIndex+=2;
                canvasImageDataIndex+=2;
            }
        }
    }

    // Module exports
    cornerstone.storedPixelDataToCanvasImageData = storedPixelDataToCanvasImageData;
    cornerstone.storedColorPixelDataToCanvasImageData = storedColorPixelDataToCanvasImageData;

   return cornerstone;
}(cornerstone));