javascript - Three.js - How to determine if a point is on a line? -

how find out if point (x,y,z) on line between pointa , pointb?

what boolean function this:

pointa        // random three.vector3 pointb        // random three.vector3 pointtocheck  // random three.vector3 var isonline = three.pointonline(pointa, pointb, pointtocheck)  if (isonline) {   console.log('point on line'); } 

here image visualization:

cross product of 2 vectors can solve problem.

function ispointonline (pointa, pointb, pointtocheck) {     var c = new three.vector3();        c.crossvectors(pointa.clone().sub(pointtocheck), pointb.clone().sub(pointtocheck));     return !c.length(); }  three.ispointonlineandbetweenpoints = function (pointa, pointb, pointtocheck) {     if (!ispointonline(pointa, pointb, pointtocheck)) {         return false;     }      var dx = pointb.x - pointa.x;     var dy = pointb.y - pointa.y;      // if line more horizontal vertical:     if (math.abs(dx) >= math.abs(dy)) {         if (dx > 0) {             return pointa.x <= pointtocheck.x && pointtocheck.x <= pointb.x;         } else {             return pointb.x <= pointtocheck.x && pointtocheck.x <= pointa.x;         }     } else {         if (dy > 0 ) {             return pointa.y <= pointtocheck.y && pointtocheck.y <= pointb.y;         } else {             return pointb.y <= pointtocheck.y && pointtocheck.y <= pointa.y;         }     } } 

a call:

three.ispointonlineandbetweenpoints(new three.vector3(1, 0, 0), new three.vector3(2, 0, 0), new three.vector3(2, 0, 0)); 

use following function if wanna know whether point on line or not:

ispointonline(new three.vector3(1, 0, 0), new three.vector3(2, 0, 0), new three.vector3(2, 0, 0));