capsule.ts

/*
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 Xiamen Yaji Software Co., Ltd. reserves all rights not expressly granted to you.

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 */

/**
 * @packageDocumentation
 * @module 3d/primitive
 */

import { Vec3 } from '../core/math';

/**
 * @en
 * The definition of the parameter for building a capsule.
 * @zh
 * 胶囊体参数选项。
 */
export interface ICapsuteOptions {
    sides: number;
    heightSegments: number;
    capped: boolean;
    arc: number;
}

const temp1 = new Vec3(0, 0, 0);
const temp2 = new Vec3(0, 0, 0);

/**
 * Generate a capsule with radiusTop radiusBottom 0.5, height 2, centered at origin,
 * but may be repositioned through the `center` option.
 * @zh
 * 生成一个胶囊体。
 * @param radiusTop 顶部半径。
 * @param radiusBottom 底部半径。
 * @param opts 胶囊体参数选项。
 */
export default function capsule (radiusTop = 0.5, radiusBottom = 0.5, height = 2, opts: RecursivePartial<ICapsuteOptions> = {}) {
    const torsoHeight = height - radiusTop - radiusBottom;
    const sides = opts.sides || 32;
    const heightSegments = opts.heightSegments || 32;
    const bottomProp = radiusBottom / height;
    const torProp = torsoHeight / height;
    const topProp = radiusTop / height;
    const bottomSegments = Math.floor(heightSegments * bottomProp);
    const topSegments = Math.floor(heightSegments * topProp);
    const torSegments = Math.floor(heightSegments * torProp);
    const topOffset = torsoHeight + radiusBottom - height / 2;
    const torOffset = radiusBottom - height / 2;
    const bottomOffset = radiusBottom - height / 2;

    const arc = opts.arc || 2.0 * Math.PI;

    // calculate vertex count
    const positions: number[] = [];
    const normals: number[] = [];
    const uvs: number[] = [];
    const indices: number[] = [];
    const maxRadius = Math.max(radiusTop, radiusBottom);
    const minPos = new Vec3(-maxRadius, -height / 2, -maxRadius);
    const maxPos = new Vec3(maxRadius, height / 2, maxRadius);
    const boundingRadius = height / 2;

    let index = 0;
    const indexArray: number[][] = [];

    generateBottom();

    generateTorso();

    generateTop();

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

    // =======================
    // internal fucntions
    // =======================

    function generateTorso () {
    // this will be used to calculate the normal
        const slope = (radiusTop - radiusBottom) / torsoHeight;

        // generate positions, normals and uvs
        for (let y = 0; y <= torSegments; y++) {
            const indexRow: number[] = [];
            const lat = y / torSegments;
            const radius = lat * (radiusTop - radiusBottom) + radiusBottom;

            for (let x = 0; x <= sides; ++x) {
                const u = x / sides;
                const v = lat * torProp + bottomProp;
                const theta = u * arc - (arc / 4);

                const sinTheta = Math.sin(theta);
                const cosTheta = Math.cos(theta);

                // vertex
                positions.push(radius * sinTheta);
                positions.push(lat * torsoHeight + torOffset);
                positions.push(radius * cosTheta);

                // normal
                Vec3.normalize(temp1, Vec3.set(temp2, sinTheta, -slope, cosTheta));
                normals.push(temp1.x);
                normals.push(temp1.y);
                normals.push(temp1.z);

                // uv
                uvs.push(u, v);
                // save index of vertex in respective row
                indexRow.push(index);

                // increase index
                ++index;
            }

            // now save positions of the row in our index array
            indexArray.push(indexRow);
        }

        // generate indices
        for (let y = 0; y < torSegments; ++y) {
            for (let x = 0; x < sides; ++x) {
                // we use the index array to access the correct indices
                const i1 = indexArray[y][x];
                const i2 = indexArray[y + 1][x];
                const i3 = indexArray[y + 1][x + 1];
                const i4 = indexArray[y][x + 1];

                // face one
                indices.push(i1);
                indices.push(i4);
                indices.push(i2);

                // face two
                indices.push(i4);
                indices.push(i3);
                indices.push(i2);
            }
        }
    }

    function generateBottom () {
        for (let lat = 0; lat <= bottomSegments; ++lat) {
            const theta = lat * Math.PI / bottomSegments / 2;
            const sinTheta = Math.sin(theta);
            const cosTheta = -Math.cos(theta);

            for (let lon = 0; lon <= sides; ++lon) {
                const phi = lon * 2 * Math.PI / sides - Math.PI / 2.0;
                const sinPhi = Math.sin(phi);
                const cosPhi = Math.cos(phi);

                const x = sinPhi * sinTheta;
                const y = cosTheta;
                const z = cosPhi * sinTheta;
                const u = lon / sides;
                const v = lat / heightSegments;

                positions.push(x * radiusBottom, y * radiusBottom + bottomOffset, z * radiusBottom);
                normals.push(x, y, z);
                uvs.push(u, v);

                if ((lat < bottomSegments) && (lon < sides)) {
                    const seg1 = sides + 1;
                    const a = seg1 * lat + lon;
                    const b = seg1 * (lat + 1) + lon;
                    const c = seg1 * (lat + 1) + lon + 1;
                    const d = seg1 * lat + lon + 1;

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

                ++index;
            }
        }
    }

    function generateTop () {
        for (let lat = 0; lat <= topSegments; ++lat) {
            const theta = lat * Math.PI / topSegments / 2 + Math.PI / 2;
            const sinTheta = Math.sin(theta);
            const cosTheta = -Math.cos(theta);

            for (let lon = 0; lon <= sides; ++lon) {
                const phi = lon * 2 * Math.PI / sides - Math.PI / 2.0;
                const sinPhi = Math.sin(phi);
                const cosPhi = Math.cos(phi);

                const x = sinPhi * sinTheta;
                const y = cosTheta;
                const z = cosPhi * sinTheta;
                const u = lon / sides;
                const v = lat / heightSegments + (1 - topProp);

                positions.push(x * radiusTop, y * radiusTop + topOffset, z * radiusTop);
                normals.push(x, y, z);
                uvs.push(u, v);

                if ((lat < topSegments) && (lon < sides)) {
                    const seg1 = sides + 1;
                    const a = seg1 * lat + lon + indexArray[torSegments][sides] + 1;
                    const b = seg1 * (lat + 1) + lon + indexArray[torSegments][sides] + 1;
                    const c = seg1 * (lat + 1) + lon + 1 + indexArray[torSegments][sides] + 1;
                    const d = seg1 * lat + lon + 1 + indexArray[torSegments][sides] + 1;

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