@woosh/meep-engine/src/core/geom/2d/triangle2d_get_barycentric.js

Pure JavaScript game engine. Fully featured and production ready.

import { v2_dot } from "../vec2/v2_dot.js";

/**
 *
 * @param {number[]|TypedArray|Float32Array} output
 * @param {number} output_offset
 * @param {number} ax
 * @param {number} ay
 * @param {number} bx
 * @param {number} by
 * @param {number} cx
 * @param {number} cy
 * @param {number} px reference point X
 * @param {number} py reference point Y
 */
export function triangle2d_get_barycentric(
    output, output_offset,
    ax, ay,
    bx, by,
    cx, cy,
    px, py
) {

    const v0_x = bx - ax;
    const v0_y = by - ay;

    const v1_x = cx - ax;
    const v1_y = cy - ay;

    const v2_x = px - ax;
    const v2_y = py - ay;

    const d00 = v2_dot(v0_x, v0_y, v0_x, v0_y);
    const d01 = v2_dot(v0_x, v0_y, v1_x, v1_y);
    const d11 = v2_dot(v1_x, v1_y, v1_x, v1_y);
    const d20 = v2_dot(v2_x, v2_y, v0_x, v0_y);
    const d21 = v2_dot(v2_x, v2_y, v1_x, v1_y);

    const denom = d00 * d11 - d01 * d01;

    const v = (d11 * d20 - d01 * d21) / denom;
    const w = (d00 * d21 - d01 * d20) / denom;
    const u = 1.0 - v - w;

    output[output_offset] = v;
    output[output_offset + 1] = w;
    output[output_offset + 2] = u;
}