three-buffergeometry-sort/index.js

Utility to sort THREE.js BufferGeometry

module.exports = (function () {
    "use strict";

    var THREE = require("three");

    var BufferGeometrySorter = function (frameSkip) {
        this.frameSkip = frameSkip || 0;
    };

    BufferGeometrySorter.prototype.sort = (function () {
        var distances = [],
            tmpPos = new THREE.Vector3(0, 0, 0),
            currFrame = 0;  // This will result in the first frame getting sorted

        return function (bufferGeomAttributes, cameraPosition) {
            if (currFrame > 0) {
                if (currFrame > this.frameSkip) {
                    // Render next frame
                    currFrame = 0;
                } else {
                    currFrame += 1;
                }
                return;
            }
            currFrame += 1;

            var attributes = bufferGeomAttributes,
                numPoints = attributes.position.count;

            for (var i = 0; i < numPoints; ++i) {
                tmpPos.set(
                    attributes.position.array[i * 3],
                    attributes.position.array[i * 3 + 1],
                    attributes.position.array[i * 3 + 2]
                );
                distances[i] = [
                    cameraPosition.distanceTo(tmpPos), i];
            }
            distances.sort(function(a, b) {
                return b[0] - a[0];
            });

            for (var val in attributes) {
                if (!attributes.hasOwnProperty(val)) { continue; }

                var itemSize = attributes[val].itemSize;
                var newArray = new Float32Array(itemSize * numPoints);

                for (i = 0; i < numPoints; ++i){
                    var index = distances[i][1];
                    for (var j = 0; j < itemSize; ++j) {
                        var srcIndex = index * itemSize + j;
                        var dstIndex = i * itemSize + j;
                        newArray[dstIndex] = attributes[val].array[srcIndex];
                    }
                }

                attributes[val].array = newArray;
                attributes[val].needsUpdate = true;
            }
        };
    }());

    return BufferGeometrySorter;
}());