@woosh/meep-engine/src/engine/graphics/texture/sampler/distance/computeSignedDistanceField_Chamfer.js

Pure JavaScript game engine. Fully featured and production ready.

import { clamp } from "../../../../../core/math/clamp.js";
import { min2 } from "../../../../../core/math/min2.js";

/**
 * algorithm proposed by Borgefors, Chamfer distance [J. ACM 15 (1968) 600, Comput. Vis. Graph. Image Process. 34 (1986) 344], h
 * @param {Sampler2D} source
 * @param {Sampler2D} distanceField
 * @param {number} emptyValue
 * @param {number} d1 distance between two adjacent pixels in either x or y direction
 * @param {number} d2 distance between two diagonally adjacent pixels
 * @param maxD
 */
export function computeSignedDistanceField_Chamfer(source, distanceField, emptyValue, d1, d2, maxD) {
    const sourceData = source.data;
    const distanceFieldData = distanceField.data;

    const width = source.width;
    const height = source.height;

    const maxX = width - 1;
    const maxY = height - 1;

    function getS(x, y) {
        x = clamp(x, 0, maxX);
        y = clamp(y, 0, maxY);

        const index = x + y * width;

        return sourceData[index];
    }

    function getD(x, y) {
        x = clamp(x, 0, maxX);
        y = clamp(y, 0, maxY);

        const index = x + y * width;

        return distanceFieldData[index];
    }

    function setD(x, y, v) {
        x = clamp(x, 0, maxX);
        y = clamp(y, 0, maxY);

        const index = x + y * width;

        distanceFieldData[index] = min2(v, maxD);
    }

    let x, y;

    //initialize distance field
    for (y = 0; y < height; y++) {
        for (x = 0; x < width; x++) {
            if (
                getS(x - 1, y) !== getS(x, y)
                || getS(x + 1, y) !== getS(x, y)
                || getS(x, y - 1) !== getS(x, y)
                || getS(x, y + 1) !== getS(x, y)
            ) {
                setD(x, y, 0);
            } else {
                setD(x, y, 255);
            }
        }
    }

    //first pass (forward)
    for (y = 0; y < height; y++) {
        for (x = 0; x < width; x++) {

            const v = getD(x, y);

            const v0 = getD(x - 1, y - 1) + d2;

            if (v0 < v) {
                setD(x, y, v0);
            }

            const v1 = getD(x, y - 1) + d1;

            if (v1 < v) {
                setD(x, y, v1);
            }

            const v2 = getD(x + 1, y - 1) + d2;

            if (v2 < v) {
                setD(x, y, v2);
            }

            const v3 = getD(x - 1, y) + d1;

            if (v3 < v) {
                setD(x, y, v3);
            }
        }
    }

    //second pass (backward)
    for (y = maxY; y >= 0; y--) {
        for (x = maxX; x >= 0; x--) {
            const v = getD(x, y);

            const v0 = getD(x + 1, y) + d1;

            if (v0 < v) {
                setD(x, y, v0);
            }

            const v1 = getD(x - 1, y + 1) + d2;

            if (v1 < v) {
                setD(x, y, v1);
            }

            const v2 = getD(x, y + 1) + d1;

            if (v2 < v) {
                setD(x, y, v2);
            }

            const v3 = getD(x + 1, y + 1) + d2;

            if (v3 < v) {
                setD(x, y, v3);
            }
        }
    }

    //indicate inside & outside
    for (y = 0; y < height; y++) {
        for (x = 0; x < width; x++) {
            if (getS(x, y) !== emptyValue) {
                //inside
                setD(x, y, -getD(x, y));
            }
        }
    }
}