Enable post-processing in VR (#20)

* Update WebXRManager.js

* Update WebGLRenderer.js

* Update WebGLRenderer.js

deleted useless blank lines

* Update WebXRManager.js

- Deleted useless code and blank lines
- refectored _getRenderTarget to getRenderTarget

* Update WebGLRenderer.js

Reflect the refactoring of getRenderTarget function

Author: enzofrancescaHM

src/renderers/WebGLRenderer.js

@@ -2335,6 +2335,13 @@ class WebGLRenderer {
 		const _scratchFrameBuffer = _gl.createFramebuffer();
 		this.setRenderTarget = function ( renderTarget, activeCubeFace = 0, activeMipmapLevel = 0 ) {
 
+			// Render to base layer instead of canvas in WebXR
+			if ( renderTarget === null && this.xr.isPresenting ) {
+
+				renderTarget = this.xr.getRenderTarget();
+
+			}
+
 			_currentRenderTarget = renderTarget;
 			_currentActiveCubeFace = activeCubeFace;
 			_currentActiveMipmapLevel = activeMipmapLevel;

src/renderers/webxr/WebXRManager.js

@@ -248,6 +248,12 @@ class WebXRManager extends EventDispatcher {
 
 		};
 
+		this.getRenderTarget = function () {
+
+			return newRenderTarget;
+
+		};
+
 		this.getFrame = function () {
 
 			return xrFrame;