Manual: add a section about limiting internal resolution to avoid performance issues

manual/en/responsive.html

@@ -257,9 +257,39 @@ <h2 id="handling-hd-dpi-displays">Handling HD-DPI displays</h2>
 <p>It might be hard to see the difference but if you have an HD-DPI
 display and you compare this sample to those above you should
 notice the edges are more crisp.</p>
+
+<h2 id="hd-dpi-limiting-maximum-drawing-buffer-size">
+  HD-DPI: Limiting maximum drawing buffer size
+</h2>
+
+<p>When using a fractional UI scaling factor on some operating system
+(eg: 150% on OSX or Linux) the assumption that the real physical
+resolution equals <code>width * window.devicePixelRatio</code> and
+<code>height * window.devicePixelRatio</code> no longer holds.
+This may lead to excessive GPU load, lower frame rates and high power 
+consumption.</p> 
+<p>A possible mitigation is to cap the maximum internal resolution (e.g. limit
+width × height) so the buffer remains within safe bounds.</p> 
+
+<pre class="prettyprint showlinemods notranslate lang-js" translate="no">    function resizeRendererToDisplaySize(renderer, maxPixelCount=3840*2160) {
+      const canvas = renderer.domElement;
+      const pixelRatio = window.devicePixelRatio;
+      let width  = Math.floor( canvas.clientWidth  * pixelRatio );
+      let height = Math.floor( canvas.clientHeight * pixelRatio );
+      const pixelCount = width * height;
+      const renderScale = pixelCount > maxPixelCount ? Math.sqrt(maxPixelCount / pixelCount) : 1;
+      width = Math.floor(width * renderScale);
+      height = Math.floor(height * renderScale);
+
+      const needResize = canvas.width !== width || canvas.height !== height;
+      if (needResize) {
+        renderer.setSize(width, height, false);
+      }
+      return needResize;
+    }
+</pre>
 <p>This article covered a very basic but fundamental topic. Next up lets quickly
 <a href="primitives.html">go over the basic primitives that three.js provides</a>.</p>
-
         </div>
       </div>
     </div>