Sphere: Add isSphere flag. (mrdoob#27395)

Author: Mugen87

docs/api/ar/math/Sphere.html

@@ -28,6 +28,9 @@ <h3>[property:Vector3 center]</h3>
 		[page:Vector3] يحدد مركز الكرة. الافتراضي هو `(0، 0،
 		0)`.
 		</p>
+
+		<h3>[property:Boolean isSphere]</h3>
+		<p>علامة للقراءة فقط للتحقق مما إذا كان كائنًا معينًا من نوع [name].</p>
 
 		<h3>[property:Float radius]</h3>
 		<p>نصف قطر الكرة. الافتراضي هو -1.</p>

docs/api/en/math/Sphere.html

@@ -29,6 +29,9 @@ <h3>[property:Vector3 center]</h3>
 			0)`.
 		</p>
 
+		<h3>[property:Boolean isSphere]</h3>
+		<p>Read-only flag to check if a given object is of type [name].</p>
+
 		<h3>[property:Float radius]</h3>
 		<p>The radius of the sphere. Default is -1.</p>
 

docs/api/it/math/Sphere.html

@@ -28,6 +28,11 @@ <h2>Proprietà</h2>
 		<h3>[property:Vector3 center]</h3>
 		<p>Un [page:Vector3] che definisce il centro della sfera. Il valore predefinito è `(0, 0, 0)`.</p>
 
+		<h3>[property:Boolean isSphere]</h3>
+		<p>
+			Flag di sola lettura per verificare se l'oggetto dato è di tipo [name].
+		</p>
+
 		<h3>[property:Float radius]</h3>
 		<p>Il raggio della sfera. Il valore predefinito è -1.</p>
 

docs/api/zh/math/Sphere.html

@@ -28,6 +28,11 @@ <h2>属性</h2>
 		<h3>[property:Vector3 center]</h3>
 		<p>A [page:Vector3]定义了球心的位置，默认值位于(0, 0, 0)。</p>
 
+		<h3>[property:Boolean isSphere]</h3>
+		<p>
+			Read-only flag to check if a given object is of type [name].
+		</p>
+
 		<h3>[property:Float radius]</h3>
 		<p>球的半径，默认值为-1。</p>
 

src/math/Sphere.js

@@ -9,6 +9,8 @@ class Sphere {
 
 	constructor( center = new Vector3(), radius = - 1 ) {
 
+		this.isSphere = true;
+
 		this.center = center;
 		this.radius = radius;
 

test/unit/src/math/Sphere.tests.js

@@ -30,6 +30,16 @@ export default QUnit.module( 'Maths', () => {
 		} );
 
 		// PUBLIC
+		QUnit.test( 'isSphere', ( assert ) => {
+
+			const a = new Sphere();
+			assert.ok( a.isSphere === true, 'Passed!' );
+
+			const b = new Box3();
+			assert.ok( ! b.isSphere, 'Passed!' );
+
+		} );
+
 		QUnit.test( 'set', ( assert ) => {
 
 			const a = new Sphere();