torus.ts

/*
 Copyright (c) 2020-2023 Xiamen Yaji Software Co., Ltd.

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 of this software and associated documentation files (the "Software"), to deal
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 THE SOFTWARE.
*/

import { Vec3 } from '../core';
import { IGeometryOptions } from './define';

/**
 * @zh
 * 环面参数选项。
 * @en
 * The options about torus
 */
interface ITorusOptions extends IGeometryOptions {
    radialSegments: number;
    tubularSegments: number;
    arc: number;
}

/**
 * @en
 * Generate a torus with radius 0.4, tube 0.1 and centered at origin.
 * @zh
 * 生成一个环面。
 * @param radius @zh 环面半径。@en The radius fo torus
 * @param tube @zh 管形大小。@en The radius of tube
 * @param opts @zh 参数选项。@en The optional creation parameters of the torus
 */
export default function torus (
    radius = 0.4,
    tube = 0.1,
    opts: RecursivePartial<ITorusOptions> = {},
): {
    positions: number[];
    normals: number[];
    uvs: number[];
    indices: number[];
    minPos: Vec3;
    maxPos: Vec3;
    boundingRadius: number;
} {
    const radialSegments = opts.radialSegments || 32;
    const tubularSegments = opts.tubularSegments || 32;
    const arc = opts.arc || 2.0 * Math.PI;

    const positions: number[] = [];
    const normals: number[] = [];
    const uvs: number[] = [];
    const indices: number[] = [];
    const minPos = new Vec3(-radius - tube, -tube, -radius - tube);
    const maxPos = new Vec3(radius + tube, tube, radius + tube);
    const boundingRadius = radius + tube;

    for (let j = 0; j <= radialSegments; j++) {
        for (let i = 0; i <= tubularSegments; i++) {
            const u = i / tubularSegments;
            const v = j / radialSegments;

            const u1 = u * arc;
            const v1 = v * Math.PI * 2;

            // vertex
            const x = (radius + tube * Math.cos(v1)) * Math.sin(u1);
            const y = tube * Math.sin(v1);
            const z = (radius + tube * Math.cos(v1)) * Math.cos(u1);

            // this vector is used to calculate the normal
            const nx = Math.sin(u1) * Math.cos(v1);
            const ny = Math.sin(v1);
            const nz = Math.cos(u1) * Math.cos(v1);

            positions.push(x, y, z);
            normals.push(nx, ny, nz);
            uvs.push(u, v);

            if ((i < tubularSegments) && (j < radialSegments)) {
                const seg1 = tubularSegments + 1;
                const a = seg1 * j + i;
                const b = seg1 * (j + 1) + i;
                const c = seg1 * (j + 1) + i + 1;
                const d = seg1 * j + i + 1;

                indices.push(a, d, b);
                indices.push(d, c, b);
            }
        }
    }

    return {
        positions,
        normals,
        uvs,
        indices,
        minPos,
        maxPos,
        boundingRadius,
    };
}