Create utils.js

utils.js

@@ -0,0 +1,49 @@
+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;
+}
+
+//polylines
+function polysIntersect(poly1, poly2){
+    for(let i=0;i<poly1.length-1;i++){
+        for(let j=0;j<poly2.length-1;j++){
+            const touch=getIntersection(
+                poly1[i],
+                poly1[i+1],
+                poly2[j],
+                poly2[j+1]
+            );
+            if(touch){
+                return true;
+            }
+        }
+    }
+    return false;
+}
+
+function getRGBA(value){
+    const alpha=Math.abs(value);
+    const R=value<0?0:255;
+    const G=R;
+    const B=value>0?0:255;
+    return "rgba("+R+","+G+","+B+","+alpha+")";
+}