src/geometryBuilders/buildBoxGeometry.js

/**
 * @desc Creates box-shaped triangle mesh geometry arrays.
 *
 * ## Usage
 *
 * In the example below we'll create an {@link XKTModel}, then create an {@link XKTMesh} with a box-shaped {@link XKTGeometry}.
 *
 * [[Run this example](http://xeokit.github.io/xeokit-sdk/examples/#geometry_builders_buildBoxGeometry)]
 *
 * ````javascript
 * const xktModel = new XKTModel();
 *
 * const box = buildBoxGeometry({
 *     primitiveType: "triangles" // or "lines"
 *     center: [0,0,0],
 *     xSize: 1,  // Half-size on each axis
 *     ySize: 1,
 *     zSize: 1
 * });
 *
 * const xktGeometry = xktModel.createGeometry({
 *      geometryId: "boxGeometry",
 *      primitiveType: box.primitiveType,
 *      positions: box.positions,
 *      normals: box.normals,
 *      indices: box.indices
 * });
 *
 * const xktMesh = xktModel.createMesh({
 *      meshId: "redBoxMesh",
 *      geometryId: "boxGeometry",
 *      position: [-4, -6, -4],
 *      scale: [1, 3, 1],
 *      rotation: [0, 0, 0],
 *      color: [1, 0, 0],
 *      opacity: 1
 * });
 *
 * const xktEntity = xktModel.createEntity({
 *      entityId: "redBox",
 *      meshIds: ["redBoxMesh"]
 *  });
 *
 * xktModel.finalize();
 * ````
 *
 * @function buildBoxGeometry
 * @param {*} [cfg] Configs
 * @param {Number[]} [cfg.center]  3D point indicating the center position.
 * @param {Number} [cfg.xSize=1.0]  Half-size on the X-axis.
 * @param {Number} [cfg.ySize=1.0]  Half-size on the Y-axis.
 * @param {Number} [cfg.zSize=1.0]  Half-size on the Z-axis.
 * @returns {Object} Geometry arrays for {@link XKTModel#createGeometry} or {@link XKTModel#createMesh}.
 */
function buildBoxGeometry(cfg = {}) {

    let xSize = cfg.xSize || 1;
    if (xSize < 0) {
        console.error("negative xSize not allowed - will invert");
        xSize *= -1;
    }

    let ySize = cfg.ySize || 1;
    if (ySize < 0) {
        console.error("negative ySize not allowed - will invert");
        ySize *= -1;
    }

    let zSize = cfg.zSize || 1;
    if (zSize < 0) {
        console.error("negative zSize not allowed - will invert");
        zSize *= -1;
    }

    const center = cfg.center;
    const centerX = center ? center[0] : 0;
    const centerY = center ? center[1] : 0;
    const centerZ = center ? center[2] : 0;

    const xmin = -xSize + centerX;
    const ymin = -ySize + centerY;
    const zmin = -zSize + centerZ;
    const xmax = xSize + centerX;
    const ymax = ySize + centerY;
    const zmax = zSize + centerZ;

    return {

        primitiveType: "triangles",

        // The vertices - eight for our cube, each
        // one spanning three array elements for X,Y and Z

        positions: [

            // v0-v1-v2-v3 front
            xmax, ymax, zmax,
            xmin, ymax, zmax,
            xmin, ymin, zmax,
            xmax, ymin, zmax,

            // v0-v3-v4-v1 right
            xmax, ymax, zmax,
            xmax, ymin, zmax,
            xmax, ymin, zmin,
            xmax, ymax, zmin,

            // v0-v1-v6-v1 top
            xmax, ymax, zmax,
            xmax, ymax, zmin,
            xmin, ymax, zmin,
            xmin, ymax, zmax,

            // v1-v6-v7-v2 left
            xmin, ymax, zmax,
            xmin, ymax, zmin,
            xmin, ymin, zmin,
            xmin, ymin, zmax,

            // v7-v4-v3-v2 bottom
            xmin, ymin, zmin,
            xmax, ymin, zmin,
            xmax, ymin, zmax,
            xmin, ymin, zmax,

            // v4-v7-v6-v1 back
            xmax, ymin, zmin,
            xmin, ymin, zmin,
            xmin, ymax, zmin,
            xmax, ymax, zmin
        ],

        // Normal vectors, one for each vertex
        normals: [

            // v0-v1-v2-v3 front
            0, 0, 1,
            0, 0, 1,
            0, 0, 1,
            0, 0, 1,

            // v0-v3-v4-v5 right
            1, 0, 0,
            1, 0, 0,
            1, 0, 0,
            1, 0, 0,

            // v0-v5-v6-v1 top
            0, 1, 0,
            0, 1, 0,
            0, 1, 0,
            0, 1, 0,

            // v1-v6-v7-v2 left
            -1, 0, 0,
            -1, 0, 0,
            -1, 0, 0,
            -1, 0, 0,

            // v7-v4-v3-v2 bottom
            0, -1, 0,
            0, -1, 0,
            0, -1, 0,
            0, -1, 0,

            // v4-v7-v6-v5 back
            0, 0, -1,
            0, 0, -1,
            0, 0, -1,
            0, 0, -1
        ],

        // UV coords
        uv: [

            // v0-v1-v2-v3 front
            1, 0,
            0, 0,
            0, 1,
            1, 1,

            // v0-v3-v4-v1 right
            0, 0,
            0, 1,
            1, 1,
            1, 0,

            // v0-v1-v6-v1 top
            1, 1,
            1, 0,
            0, 0,
            0, 1,

            // v1-v6-v7-v2 left
            1, 0,
            0, 0,
            0, 1,
            1, 1,

            // v7-v4-v3-v2 bottom
            0, 1,
            1, 1,
            1, 0,
            0, 0,

            // v4-v7-v6-v1 back
            0, 1,
            1, 1,
            1, 0,
            0, 0
        ],

        // Indices - these organise the
        // positions and uv texture coordinates
        // into geometric primitives in accordance
        // with the "primitive" parameter,
        // in this case a set of three indices
        // for each triangle.
        //
        // Note that each triangle is specified
        // in counter-clockwise winding order.
        //
        // You can specify them in clockwise
        // order if you configure the Modes
        // node's frontFace flag as "cw", instead of
        // the default "ccw".
        indices: [
            0, 1, 2,
            0, 2, 3,
            // front
            4, 5, 6,
            4, 6, 7,
            // right
            8, 9, 10,
            8, 10, 11,
            // top
            12, 13, 14,
            12, 14, 15,
            // left
            16, 17, 18,
            16, 18, 19,
            // bottom
            20, 21, 22,
            20, 22, 23
        ]
    };
}

export {buildBoxGeometry};