Merge pull request #14822 from WestLangley/dev-mtlloader_alphamap

MTLLoader: added support for alphaMap

examples/js/loaders/MTLLoader.js

@@ -445,6 +445,15 @@ THREE.MTLLoader.MaterialCreator.prototype = {
 
 					break;
 
+				case 'map_d':
+
+					// Alpha map
+
+					setMapForType( "alphaMap", value );
+					params.transparent = true;
+
+					break;
+
 				case 'ns':
 
 					// The specular exponent (defines the focus of the specular highlight)