normalize directionalLight directions

Author: Spongman

src/webgl/light.js

@@ -170,7 +170,9 @@ p5.prototype.directionalLight = function(v1, v2, v3, x, y, z) {
   //in case there's no material color for the geometry
   shader.setUniform('uMaterialColor', this._renderer.curFillColor);
 
-  this._renderer.directionalLightDirections.push(_x, _y, _z);
+  // normalize direction
+  var l = Math.sqrt(_x * _x + _y * _y + _z * _z);
+  this._renderer.directionalLightDirections.push(_x / l, _y / l, _z / l);
   shader.setUniform(
     'uLightingDirection',
     this._renderer.directionalLightDirections