WebGLRenderer: Maybe it's better to use setViewport without arguments for resetting.

src/renderers/WebGLRenderer.js

@@ -222,20 +222,15 @@ THREE.WebGLRenderer = function ( parameters ) {
 
 	this.setViewport = function ( x, y, width, height ) {
 
-		_viewportX = x;
-		_viewportY = y;
+		_viewportX = x !== undefined ? x : 0;
+		_viewportY = y !== undefined ? y : 0;
 
-		_viewportWidth = width;
-		_viewportHeight = height;
+		_viewportWidth = width !== undefined ? width : _canvas.width;
+		_viewportHeight = height !== undefined ? height : _canvas.height;
 
 		_gl.viewport( _viewportX, _viewportY, _viewportWidth, _viewportHeight );
 
 	};
-	
-	//reset the viewport to the current canvas size
-	this.resetViewport = function () {
-		this.setViewport( 0, 0, _canvas.width, _canvas.height );
-	}
 
 	this.setScissor = function ( x, y, width, height ) {