utils.js

function lerp(A, B, t){
    return A + (B - A) * t;
}

function getIntersection(A, B, C ,D){
    const tTop = (D.x - C.x) * (A.y - C.y) - (D.y - C.y) * (A.x - C.x);
    const uTop = (C.y - A.y) * (A.x - B.x) - (C.x - A.x) * (A.y - B.y);
    const bottom = (D.y - C.y) * (B.x - A.x) - (D.x - C.x) * (B.y - A.y);

    if (bottom != 0){
        const t = tTop / bottom;
        const u = uTop / bottom;
        if (t >= 0 && t <= 1 && u >= 0 && u <= 1){
            return{
                x: lerp(A.x, B.x, t),
                y: lerp(A.y, B.y, t),
                offset: t
            }
        }
    }
    
    return null;
}

function polyIntersect(poly1, poly2){
    for (let i = 0; i < poly1.length; i++){
        for (let j = 0; j < poly2.length; j++){
            const touch = getIntersection(poly1[i], poly1[(i+1)%poly1.length],
                poly2[j], poly2[(j+1)%poly2.length]);
            if (touch){
                return true;
            }
        }
    }
    return false;
}