CanvasRenderer/SVGRenderer: Discard elements with material.opacity === 0. Fixes #4617.

examples/js/renderers/SVGRenderer.js

@@ -123,7 +123,7 @@ THREE.SVGRenderer = function () {
 			var element = _elements[ e ];
 			var material = element.material;
 
-			if ( material === undefined || material.visible === false ) continue;
+			if ( material === undefined || material.opacity === 0 ) continue;
 
 			_elemBox.makeEmpty();
 

src/renderers/CanvasRenderer.js

@@ -275,7 +275,7 @@ THREE.CanvasRenderer = function ( parameters ) {
 
 			var material = element.material;
 
-			if ( material === undefined || material.visible === false ) continue;
+			if ( material === undefined || material.opacity === 0 ) continue;
 
 			_elemBox.makeEmpty();