Merge pull request #13377 from takahirox/GLTFExporterCubicSpline

GLTFExporter: CubicSpline interpolation support

examples/js/exporters/GLTFExporter.js

@@ -962,7 +962,6 @@ THREE.GLTFExporter.prototype = {
 		 *
 		 * Status:
 		 * - Only properties listed in PATH_PROPERTIES may be animated.
-		 * - Only LINEAR and STEP interpolation currently supported.
 		 *
 		 * @param {THREE.AnimationClip} clip
 		 * @param {THREE.Object3D} root
@@ -1016,11 +1015,37 @@ THREE.GLTFExporter.prototype = {
 
 				}
 
+				var interpolation;
+
+				// @TODO export CubicInterpolant(InterpolateSmooth) as CUBICSPLINE
+
+				// Detecting glTF cubic spline interpolant by checking factory method's special property
+				// GLTFCubicSplineInterpolant is a custom interpolant and track doesn't return
+				// valid value from .getInterpolation().
+				if ( track.createInterpolant.isInterpolantFactoryMethodGLTFCubicSpline === true ) {
+
+					interpolation = 'CUBICSPLINE';
+
+					// itemSize of CUBICSPLINE keyframe is 9
+					// (VEC3 * 3: inTangent, splineVertex, and outTangent)
+					// but needs to be stored as VEC3 so dividing by 3 here.
+					outputItemSize /= 3;
+
+				} else if ( track.getInterpolation() === THREE.InterpolateDiscrete ) {
+
+					interpolation = 'STEP';
+
+				} else {
+
+					interpolation = 'LINEAR';
+
+				}
+
 				samplers.push( {
 
 					input: processAccessor( new THREE.BufferAttribute( track.times, inputItemSize ) ),
 					output: processAccessor( new THREE.BufferAttribute( track.values, outputItemSize ) ),
-					interpolation: track.getInterpolation() === THREE.InterpolateDiscrete ? 'STEP' : 'LINEAR'
+					interpolation: interpolation
 
 				} );
 

examples/js/loaders/GLTFLoader.js

@@ -2464,7 +2464,7 @@ THREE.GLTFLoader = ( function () {
 							// Overrides .createInterpolant in a factory method which creates custom interpolation.
 							if ( sampler.interpolation === 'CUBICSPLINE' ) {
 
-								track.createInterpolant = function ( result ) {
+								track.createInterpolant = function InterpolantFactoryMethodGLTFCubicSpline( result ) {
 
 									// A CUBICSPLINE keyframe in glTF has three output values for each input value,
 									// representing inTangent, splineVertex, and outTangent. As a result, track.getValueSize()
@@ -2474,6 +2474,10 @@ 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.
+								track.createInterpolant.isInterpolantFactoryMethodGLTFCubicSpline = true;
+
 							}
 
 							tracks.push( track );