support all types of animation interpolation from gltf

[mockersf]

Objective

• Support step and cubic spline interpolation from gltf

Solution

• Support step and cubic spline interpolation from gltf

Tested with https://github.com/KhronosGroup/glTF-Sample-Models/tree/master/2.0/InterpolationTest
expected:

result:

---

Migration Guide

When manually specifying an animation VariableCurve, the interpolation type must be specified:

• Bevy 0.12

        VariableCurve {
            keyframe_timestamps: vec![0.0, 1.0, 2.0, 3.0, 4.0],
            keyframes: Keyframes::Rotation(vec![
                Quat::IDENTITY,
                Quat::from_axis_angle(Vec3::Y, PI / 2.),
                Quat::from_axis_angle(Vec3::Y, PI / 2. * 2.),
                Quat::from_axis_angle(Vec3::Y, PI / 2. * 3.),
                Quat::IDENTITY,
            ]),
        },

• Bevy 0.13

        VariableCurve {
            keyframe_timestamps: vec![0.0, 1.0, 2.0, 3.0, 4.0],
            keyframes: Keyframes::Rotation(vec![
                Quat::IDENTITY,
                Quat::from_axis_angle(Vec3::Y, PI / 2.),
                Quat::from_axis_angle(Vec3::Y, PI / 2. * 2.),
                Quat::from_axis_angle(Vec3::Y, PI / 2. * 3.),
                Quat::IDENTITY,
            ]),
            interpolation: Interpolation::Linear,
        },

[james7132]

Just a cursory initial scan through. I'll do a full review at a later point in time.

[alice-i-cecile]

TIL that GLTF only supports those modes :( https://github.com/KhronosGroup/glTF-Tutorials/blob/master/gltfTutorial/gltfTutorial_007_Animations.md#interpolation

[james7132]

Sorry for the long delay on this review! Everything looks good to me now.

[torsteingrindvik]

@alice-i-cecile or @james7132 should this get the ready for final review label?

I'm hoping this PR fixes a GLTF scene I have which uses step interpolation.

[torsteingrindvik]

I tried this PR on my model which is broken on main due to it using step interpolation and this PR fixes that.

[nicopap]

LGTM

[mockersf]

added the requested comment, can be merged now 👍