[pull] dev from mrdoob:dev

manual/pages/installation.html

@@ -253,7 +253,7 @@ <h3>Production</h3>
             <i><b>IMPORTANT:</b> Import all dependencies from the same version of three.js, and from the same CDN. Mixing files from different sources may cause duplicate code to be included, or even break the application in unexpected ways.</i>
           </p>
 
-          <h2>Addons</h2>
+          <h2 id="addons">Addons</h2>
 
           <p>
             Out of the box, three.js includes the fundamentals of a 3D engine. Other three.js components — such as controls, loaders, and post-processing effects — are part of the [link:https://github.com/mrdoob/three.js/tree/dev/examples/jsm addons/] directory. Addons do not need to be <i>installed</i> separately, but do need to be <i>imported</i> separately.

src/math/Ray.js

@@ -306,6 +306,8 @@ class Ray {
 	 */
 	intersectSphere( sphere, target ) {
 
+		if ( sphere.radius < 0 ) return null; // handle empty spheres, see #31187
+
 		_vector.subVectors( sphere.center, this.origin );
 		const tca = _vector.dot( this.direction );
 		const d2 = _vector.dot( _vector ) - tca * tca;

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

@@ -260,6 +260,13 @@ export default QUnit.module( 'Maths', () => {
 			a0.intersectSphere( b, point );
 			assert.ok( point.distanceTo( new Vector3( 0, 0, - 5 ) ) < TOL, 'Passed!' );
 
+			// empty sphere ( negative radius ) can never be intersected, so the
+			// target must be left untouched and the return value must be null,
+			// consistent with intersectsSphere()
+			b = new Sphere( new Vector3( 0, 0, - 1 ), - 1 );
+			assert.strictEqual( a0.intersectSphere( b, point.copy( posInf3 ) ), null, 'Passed!' );
+			assert.ok( point.equals( posInf3 ), 'Passed!' );
+
 		} );
 
 		QUnit.test( 'intersectsSphere', ( assert ) => {

utils/docs/template/tmpl/container.tmpl

@@ -42,7 +42,7 @@
 			<article>
 				<?js if (doc.import) { ?>
 				<h2 class="subsection-title">Import</h2>
-				<p><span translate="no"><?js= doc.name ?></span> is an addon, and must be imported explicitly, see <a href="https://threejs.org/manual/#installation">Installation#Addons</a>.</p>
+				<p><span translate="no"><?js= doc.name ?></span> is an addon, and must be imported explicitly, see <a href="https://threejs.org/manual/#installation#addons">Installation#Addons</a>.</p>
 				<pre class="prettyprint source lang-js" translate="no"><code><?js= doc.import ?></code></pre>
 				<?js } ?>
 				<div class="container-overview">