utils.js

//lerp funtion calcs the linear interpolation between two points
function lerp(a,b,t){
    return a+(b-a)*t;
}

//get intersection function is used to find the intersection between two
// lines

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 polysIntersect(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;
}

function getRandomcolor(){
    const hue = 290 + Math.random()*260;
    return "hsl("+hue+", 100%, 60%)";
}