Builds vertex and index arrays as needed for xeoEngine's color-indexed triangle picking.

XEO.math.getPickPrimitives.js

/**
 * Builds vertex and index arrays needed by color-indexed triangle picking.
 *
 * @method getPickPrimitives
 * @static
 * @param {Float32Array} positions One-dimensional flattened array of positions.
 * @param {Float32Array} indices One-dimensional flattened array of indices.
 * @returns {*} Object containing the arrays, created by this method or reused from 'pickTris' parameter.
 */
getPickPrimitives: function(positions, indices) {

    var numIndices = indices.length;

    var pickPositions = new Float32Array(numIndices * 30); // FIXME: Why do we need to extend size like this to make large meshes pickable?
    var pickColors = new Float32Array(numIndices * 40);

    var primIndex = 0;

    // Positions array index
    var vi;

    // Picking positions array index
    var pvi;

    // Picking color array index
    var pci;

    // Triangle indices

    var i;
    var r;
    var g;
    var b;
    var a;

    for (var location = 0; location < numIndices; location += 3) {

        pvi = location * 3;
        pci = location * 4;

        // Primitive-indexed triangle pick color

        a = (primIndex >> 24 & 0xFF) / 255.0;
        b = (primIndex >> 16 & 0xFF) / 255.0;
        g = (primIndex >> 8 & 0xFF) / 255.0;
        r = (primIndex & 0xFF) / 255.0;

        // A

        i = indices[location];
        vi = i * 3;

        pickPositions[pvi] = positions[vi];
        pickPositions[pvi + 1] = positions[vi + 1];
        pickPositions[pvi + 2] = positions[vi + 2];

        pickColors[pci] = r;
        pickColors[pci + 1] = g;
        pickColors[pci + 2] = b;
        pickColors[pci + 3] = a;


        // B

        i = indices[location + 1];
        vi = i * 3;

        pickPositions[pvi + 3] = positions[vi];
        pickPositions[pvi + 4] = positions[vi + 1];
        pickPositions[pvi + 5] = positions[vi + 2];

        pickColors[pci + 4] = r;
        pickColors[pci + 5] = g;
        pickColors[pci + 6] = b;
        pickColors[pci + 7] = a;


        // C

        i = indices[location + 2];
        vi = i * 3;

        pickPositions[pvi + 6] = positions[vi];
        pickPositions[pvi + 7] = positions[vi + 1];
        pickPositions[pvi + 8] = positions[vi + 2];

        pickColors[pci + 8] = r;
        pickColors[pci + 9] = g;
        pickColors[pci + 10] = b;
        pickColors[pci + 11] = a;

        primIndex++;
    }

    return {
        positions: pickPositions,
        colors: pickColors
    };
},