### Jordan Savant # Software Engineer

``````/*
Return the angle between two vectors on a plane
The angle is from vector 1 to vector 2, positive anticlockwise
The result is between -pi -> pi
*/
function Angle2D(x1, y1, x2, y2) {
let dtheta,theta1,theta2;

theta1 = Math.atan2(y1,x1);
theta2 = Math.atan2(y2,x2);
dtheta = theta2 - theta1;
while (dtheta > Math.PI)
dtheta -= Math.PI * 2;
while (dtheta < -Math.PI)
dtheta += Math.PI * 2;
return dtheta;
}

function InsidePolygon(polygon, p) {
let i;
let angle=0;
let p1 = {}, p2 = {};
let n = polygon.points.length;

for (i=0; i < n; i++) {
p1.h = polygon.points[i].x - p.x;
p1.v = polygon.points[i].y - p.y;
p2.h = polygon.points[(i+1)%n].x - p.x;
p2.v = polygon.points[(i+1)%n].y - p.y;
angle += Angle2D(p1.h,p1.v,p2.h,p2.v);
}

if (Math.abs(angle) < Math.PI)
return false
else
return true
}
``````

example of wired into mousemovement

``````c.onmousemove = function(e){
if (!listening)
return

data.innerHTML = '';
data.style.display = 'none';
mouseX = e.clientX;
mouseY = e.clientY;

// convert to canvas coords
let cpos = getOffset(c);
let cx = mouseX - cpos.rawleft;
let cy = mouseY - cpos.rawtop;

if (cx > 0 && cx < cpos.rawwidth && cy > 0 && cy < cpos.rawheight) {
// get mouse position in polygon
let inside = false;
for (let i=0; i < polygons.length; i++) {
if (InsidePolygon(polygons[i], { x: cx, y: cy })) {
// console.log("INSIDE ", polygons[i].id)
data.innerHTML = '{{ \$refName }} ' + polygons[i].id;
inside = true;
}
}
if (inside) {
data.style.display = 'block';
data.style.top = mouseY - 10;
data.style.left = mouseX + 10;
}
}
}``````