feat(dotProduct): Added dot-product function

Author: terkelg

src/dot-product.js

@@ -0,0 +1,23 @@
+/**
+ * Compute the dot product of any pair of 2D vectors.
+ *
+ * @param  {number} x0 - First x start position.
+ * @param  {number} y0 - First y start position.
+ * @param  {number} x1 - First x end position.
+ * @param  {number} y1 - First y end position.
+ * @param  {number} x2 - Second x start position.
+ * @param  {number} y2 - Second y start position.
+ * @param  {number} x3 - Second x end position.
+ * @param  {number} y3 - Second y end position.
+ * @return {number} Dot product.
+ */
+function dotProduct (x0, y0, x1, y1, x2, y2, x3, y3) {
+  let dx0 = x1 - x0
+  let dy0 = y1 - y0
+  let dx1 = x3 - x2
+  let dy1 = y3 - y2
+
+  return dx0 * dx1 + dy0 * dy1
+}
+
+export { dotProduct }

src/math-toolbox.js

@@ -49,3 +49,4 @@ export { smoothMin } from './smooth-min'
 export { smoothMax } from './smooth-max'
 export { deltaTime } from './delta-time'
 export { gcd } from './gcd'
+export { dotProduct } from './dot-product'