@joie, sorry for the delay in my response. As far as I know, glTF does not support one parameter morphing between multiple shape states. The way I would normally pass from one shape through another to the end shape is by cross fading the influences like this example.
Here I’ve started with a cube, morph to a sphere before ending on the hemisphere and then back out again. The cube => sphere and cube => hemisphere morphs are two different influences, but if you cross fade the animations, you will appear to move through a different shape to reach the end shape. This is what I mean by the cross fade:
This is how the influences change in order to produce cube => sphere => hemisphere => sphere => cube morph:
- sphere influence moves to 1.0, hemisphere influence remains at 0.0
- sphere influence moves to 0.0 at the same rate at hemisphere influence moves to 1.0
- hemisphere influence moves to 0.0 at the same rate as sphere influence moves to 1.0
- sphere influence moves to 0.0 while hemisphere influence remains at 0.0
I realize that needing to handle two influence values instead of one makes for a more complicated animation process. However, I would suggest creating a control rig that you can map a single value to lerp the values of the multiple influence values. I haven’t made a rig like this for glTF, but you should be able to either export or bake the correct data into the glTF so that your animations retain your authored motion but also fit within the glTF spec.
I hope this helps, but please feel free to ping me with more questions.