BufferGeometry: Add warning on .merge().

examples/js/loaders/GLTFLoader.js

@@ -2174,10 +2174,10 @@ THREE.GLTFLoader = ( function () {
 					}
 
 					// If the material will be modified later on, clone it now.
-					var useSkinning = meshDef.isSkinnedMesh === true;
-					var useMorphTargets = primitive.targets !== undefined;
 					var useVertexColors = geometry.attributes.color !== undefined;
 					var useFlatShading = geometry.attributes.normal === undefined;
+					var useSkinning = meshDef.isSkinnedMesh === true;
+					var useMorphTargets = primitive.targets !== undefined;
 
 					if ( useVertexColors || useFlatShading || useSkinning || useMorphTargets ) {
 

src/core/BufferGeometry.js

@@ -794,7 +794,16 @@ BufferGeometry.prototype = Object.assign( Object.create( EventDispatcher.prototy
 
 		}
 
-		if ( offset === undefined ) offset = 0;
+		if ( offset === undefined ) {
+
+			offset = 0;
+
+			console.warn(
+				'THREE.BufferGeometry.merge(): Overwriting original geometry, starting at offset=0. '
+				+ 'Use BufferGeometryUtils.mergeBufferGeometries() for lossless merge.'
+			);
+
+		}
 
 		var attributes = this.attributes;