GLTFLoader: Fix warning on cubicspline interpolation.

examples/js/loaders/GLTFLoader.js

@@ -1218,10 +1218,8 @@ THREE.GLTFLoader = ( function () {
 	};
 
 	var INTERPOLATION = {
-		CUBICSPLINE: THREE.InterpolateSmooth, // We use custom interpolation GLTFCubicSplineInterpolation for CUBICSPLINE.
-		                                      // KeyframeTrack.optimize() can't handle glTF Cubic Spline output values layout,
-		                                      // using THREE.InterpolateSmooth for KeyframeTrack instantiation to prevent optimization.
-		                                      // See KeyframeTrack.optimize() for the detail.
+		CUBICSPLINE: undefined, // We use a custom interpolant (GLTFCubicSplineInterpolation) for CUBICSPLINE tracks. Each
+		                        // keyframe track will be initialized with a default interpolation type, then modified.
 		LINEAR: THREE.InterpolateLinear,
 		STEP: THREE.InterpolateDiscrete
 	};
@@ -2880,10 +2878,7 @@ THREE.GLTFLoader = ( function () {
 
 				if ( PATH_PROPERTIES[ target.path ] === PATH_PROPERTIES.weights ) {
 
-					// node can be THREE.Group here but
-					// PATH_PROPERTIES.weights(morphTargetInfluences) should be
-					// the property of a mesh object under group.
-
+					// Node may be a THREE.Group (glTF mesh with several primitives) or a THREE.Mesh.
 					node.traverse( function ( object ) {
 
 						if ( object.isMesh === true && object.morphTargetInfluences ) {
@@ -2900,20 +2895,16 @@ THREE.GLTFLoader = ( function () {
 
 				}
 
-				// KeyframeTrack.optimize() will modify given 'times' and 'values'
-				// buffers before creating a truncated copy to keep. Because buffers may
-				// be reused by other tracks, make copies here.
 				for ( var j = 0, jl = targetNames.length; j < jl; j ++ ) {
 
 					var track = new TypedKeyframeTrack(
 						targetNames[ j ] + '.' + PATH_PROPERTIES[ target.path ],
-						THREE.AnimationUtils.arraySlice( inputAccessor.array, 0 ),
-						THREE.AnimationUtils.arraySlice( outputAccessor.array, 0 ),
+						inputAccessor.array,
+						outputAccessor.array,
 						interpolation
 					);
 
-					// Here is the trick to enable custom interpolation.
-					// Overrides .createInterpolant in a factory method which creates custom interpolation.
+					// Override interpolation with custom factory method.
 					if ( sampler.interpolation === 'CUBICSPLINE' ) {
 
 						track.createInterpolant = function InterpolantFactoryMethodGLTFCubicSpline( result ) {
@@ -2926,8 +2917,7 @@ THREE.GLTFLoader = ( function () {
 
 						};
 
-						// Workaround, provide an alternate way to know if the interpolant type is cubis spline to track.
-						// track.getInterpolation() doesn't return valid value for custom interpolant.
+						// Mark as CUBICSPLINE. `track.getInterpolation()` doesn't support custom interpolants.
 						track.createInterpolant.isInterpolantFactoryMethodGLTFCubicSpline = true;
 
 					}