Gltf export blend shape

[fire]

Work on gltf export.

Fixes: #47121

GLTF Export blend shape notes from Lyuma

This code is invalid:

                        Color tangent;
                        tangent.r = tarr[(i * 4) + 0];
                        tangent.g = tarr[(i * 4) + 1];
                        tangent.b = tarr[(i * 4) + 2];
                        tangent.a = tarr[(i * 4) + 3];
                        Vector3 vec3;
                        vec3.x = tarr[(i * 4) + 0];
                        vec3.y = tarr[(i * 4) + 1];
                        vec3.z = tarr[(i * 4) + 2];
                        vec3 *= tarr[(i * 4) + 3] * -1;
                    }

If TANGENT is encoded as vec3, the w component should be dropped, not multiplied.

This code has a bug:

                Vector<Vector3> narr = array_morph[Mesh::ARRAY_NORMAL];
                if (varr.size()) {
                    t["NORMAL"] = _encode_accessor_as_vec3(state, narr, true);
                }

Should be if(narr.size()) {

Line 6262: If we encounter another :blend_shapes/ track for a mesh whose blend shapes we have already exported, we must avoid exporting the blend shapes for that mesh a second time.

keyframes should be capped at a constant * the original number of keyframes. for example, min of 1.0 / BAKE_FPS and (total length / (10 * number of keyframes))

We should check if tracks are linear and avoid the complicated baking cases.

blend shape A   ..      . .    .
blend shape O   .    . .   .   .
->
output          ..   . .. ..   .

Line 6358: change to if key_count == 0: Why two zeros? I think we should do only one key

                weight.times.push_back(0.0f);
                weight.times.push_back(0.0f);
                weight.values.push_back(0.0f);
                weight.values.push_back(0.0f);
                track.weight_tracks.push_back(weight);

[fire]

Remaining issues.

Line 6262: If we encounter another :blend_shapes/ track for a mesh whose blend shapes we have already exported, we must avoid exporting the blend shapes for that mesh a second time.

keyframes should be capped at a constant * the original number of keyframes. for example, min of 1.0 / BAKE_FPS and (total length / (10 * number of keyframes))

We should check if tracks are linear and avoid the complicated baking cases.

Edited:

Removed tangent export for blend shapes (morph targets).

[fire]

Superseded by: #50019