code: function setupDepthRenderbuffer( renderTarget ) {
  
  		var renderTargetProperties = properties.get( renderTarget );
  
  		var isCube = ( renderTarget instanceof THREE.WebGLRenderTargetCube );
  
  		if ( renderTarget.depthTexture ) {
  
  			if ( isCube ) throw new Error('target.depthTexture not supported in Cube render targets');
  
  			setupDepthTexture( renderTargetProperties.__webglFramebuffer, renderTarget );
  
  		} else {
  
  			if ( isCube ) {
  
  				renderTargetProperties.__webglDepthbuffer = [];
  
  				for ( var i = 0; i < 6; i ++ ) {
  
  					_gl.bindFramebuffer( _gl.FRAMEBUFFER, renderTargetProperties.__webglFramebuffer[ i ] );
  					renderTargetProperties.__webglDepthbuffer[ i ] = _gl.createRenderbuffer();
  					setupRenderBufferStorage( renderTargetProperties.__webglDepthbuffer[ i ], renderTarget );
  
  				}
  
  			} else {
  
  				_gl.bindFramebuffer( _gl.FRAMEBUFFER, renderTargetProperties.__webglFramebuffer );
  				renderTargetProperties.__webglDepthbuffer = _gl.createRenderbuffer();
  				setupRenderBufferStorage( renderTargetProperties.__webglDepthbuffer, renderTarget );
  
  			}
  
  		}
  
  		_gl.bindFramebuffer( _gl.FRAMEBUFFER, null );
  
  	}
docs: Setup GL resources for a non-texture depth buffer