Add API for the attached renderer

Resolves #1281

src/virtual-machine.js

@@ -958,6 +958,13 @@ class VirtualMachine extends EventEmitter {
         this.runtime.attachRenderer(renderer);
     }
 
+    /**
+     * @returns {RenderWebGL} The renderer attached to the vm
+     */
+    get renderer () {
+        return this.runtime && this.runtime.renderer;
+    }
+
     /**
      * Set the svg adapter for the VM/runtime, which converts scratch 2 svgs to scratch 3 svgs
      * @param {!SvgRenderer} svgAdapter The adapter to attach

test/unit/virtual-machine.js

@@ -4,6 +4,7 @@ const Sprite = require('../../src/sprites/sprite');
 const Variable = require('../../src/engine/variable');
 const adapter = require('../../src/engine/adapter');
 const events = require('../fixtures/events.json');
+const Renderer = require('../fixtures/fake-renderer');
 const Runtime = require('../../src/engine/runtime');
 const RenderedTarget = require('../../src/sprites/rendered-target');
 
@@ -928,3 +929,11 @@ test('Setting turbo mode emits events', t => {
 
     t.end();
 });
+
+test('Getting the renderer returns the renderer', t => {
+    const renderer = new Renderer();
+    const vm = new VirtualMachine();
+    vm.attachRenderer(renderer);
+    t.equal(vm.renderer, renderer);
+    t.end();
+});