feat(rendering): add option to enable stencil buffer (#15)

Summary:
This adds the option to enable drawing to the stencil buffer on the default renderer in IWSDK.

This is purely optional and makes it possible to do the magic window effect commonly used in mixed reality applications.

Pull Request resolved: #15

Reviewed By: felixtrz

Differential Revision: D87954435

Pulled By: zjm-meta

fbshipit-source-id: afe8a8e9674eddba8020fdf04b42bb3c10ad0c61

Author: “Florian

packages/core/src/init/world-initializer.ts

@@ -93,6 +93,8 @@ export type WorldOptions = {
     far?: number;
     /** Generate a default gradient environment and background. @defaultValue true */
     defaultLighting?: boolean;
+    /** Enable stencil buffer. @defaultValue false */
+    stencil?: boolean;
   };
 
   /** Opt‑in feature systems. */
@@ -222,6 +224,7 @@ function extractConfiguration(options: WorldOptions) {
     cameraNear: options.render?.near ?? 0.1,
     cameraFar: options.render?.far ?? 200,
     defaultLighting: options.render?.defaultLighting ?? true,
+    stencil: options.render?.stencil ?? false,
     xr: {
       sessionMode: options.xr?.sessionMode ?? SessionMode.ImmersiveVR,
       referenceSpace:
@@ -260,6 +263,7 @@ function setupRendering(sceneContainer: HTMLDivElement, config: any) {
     alpha: config.xr.sessionMode === SessionMode.ImmersiveAR,
     // @ts-ignore
     multiviewStereo: true,
+    stencil: config.stencil,
   });
   renderer.setPixelRatio(window.devicePixelRatio);
   renderer.setSize(window.innerWidth, window.innerHeight);