use symmetric half up rounding in all vector modules. fixes #447

spec/gl-matrix/vec2-spec.js

@@ -259,6 +259,10 @@ describe("vec2", function() {
             it("should place values into vecA", function() { expect(vecA).toBeEqualish([3, 3]); });
             it("should return vecA", function() { expect(result).toBe(vecA); });
         });
+
+        describe("symmetry", function() {
+            it("should round negative values torwards negative infinity", function() { expect(vec2.round([], [-1.5, -1.5])).toBeEqualish([-2, -2]); });
+        });
     });
 
     describe("scale", function() {

spec/gl-matrix/vec3-spec.js

@@ -400,6 +400,10 @@ describe("vec3", function() {
             it("should place values into vecA", function() { expect(vecA).toBeEqualish([3, 3, 1]); });
             it("should return vecA", function() { expect(result).toBe(vecA); });
         });
+
+        describe("symmetry", function() {
+            it("should round negative values torwards negative infinity", function() { expect(vec3.round([], [-1.5, -1.5, -2.5])).toBeEqualish([-2, -2, -3]); });
+        });
     });
 
     describe("scale", function() {

spec/gl-matrix/vec4-spec.js

@@ -260,6 +260,10 @@ describe("vec4", function() {
             it("should place values into vecA", function() { expect(vecA).toBeEqualish([3, 3, 1, 1]); });
             it("should return vecA", function() { expect(result).toBe(vecA); });
         });
+
+        describe("symmetry", function() {
+            it("should round negative values torwards negative infinity", function() { expect(vec4.round([], [-1.5, -1.5, -2.5, -0.5 ])).toBeEqualish([-2, -2, -3, -1]); });
+        });
     });
 
     describe("scale", function() {

src/common.js

@@ -10,6 +10,19 @@ export let ARRAY_TYPE =
 export let RANDOM = Math.random;
 export let ANGLE_ORDER = "zyx";
 
+/**
+ * Symmetric round
+ * see https://www.npmjs.com/package/round-half-up-symmetric#user-content-detailed-background
+ *
+ * @param {Number} a value to round
+ */
+export function round(a) {
+  if (a >= 0)
+    return Math.round(a);
+
+  return (a % 0.5 === 0) ? Math.floor(a) : Math.round(a);
+}
+
 /**
  * Sets the type of array used when creating new vectors and matrices
  *

src/vec2.js

@@ -184,15 +184,15 @@ export function max(out, a, b) {
 }
 
 /**
- * Math.round the components of a vec2
+ * symmetric round the components of a vec2
  *
  * @param {vec2} out the receiving vector
  * @param {ReadonlyVec2} a vector to round
  * @returns {vec2} out
  */
 export function round(out, a) {
-  out[0] = Math.round(a[0]);
-  out[1] = Math.round(a[1]);
+  out[0] = glMatrix.round(a[0]);
+  out[1] = glMatrix.round(a[1]);
   return out;
 }
 

src/vec3.js

@@ -212,16 +212,16 @@ export function max(out, a, b) {
 }
 
 /**
- * Math.round the components of a vec3
+ * symmetric round the components of a vec3
  *
  * @param {vec3} out the receiving vector
  * @param {ReadonlyVec3} a vector to round
  * @returns {vec3} out
  */
 export function round(out, a) {
-  out[0] = Math.round(a[0]);
-  out[1] = Math.round(a[1]);
-  out[2] = Math.round(a[2]);
+  out[0] = glMatrix.round(a[0]);
+  out[1] = glMatrix.round(a[1]);
+  out[2] = glMatrix.round(a[2]);
   return out;
 }
 

src/vec4.js

@@ -214,17 +214,17 @@ export function max(out, a, b) {
 }
 
 /**
- * Math.round the components of a vec4
+ * symmetric round the components of a vec4
  *
  * @param {vec4} out the receiving vector
  * @param {ReadonlyVec4} a vector to round
  * @returns {vec4} out
  */
 export function round(out, a) {
-  out[0] = Math.round(a[0]);
-  out[1] = Math.round(a[1]);
-  out[2] = Math.round(a[2]);
-  out[3] = Math.round(a[3]);
+  out[0] = glMatrix.round(a[0]);
+  out[1] = glMatrix.round(a[1]);
+  out[2] = glMatrix.round(a[2]);
+  out[3] = glMatrix.round(a[3]);
   return out;
 }