How to change the animated node value

[Idriss]

Hi,

I have read the specification sheet of glTF, and in Animation I found 2 set of vectors; input and output, so imagine that I want to use OpenGL to render the content, how can I do it?
I have to start a timer and then set at every key frame the value of translation rotation scale or either weights? how I can accomplish this method?
I have to update the VBO at each frame?

thanks

[donmccurdy]

You may get better answers for this on the OpenGL section (https://community.khronos.org/c/opengl-general/34) since the technique is not specific to glTF or any particular file format. But in general terms:

The “keyframes” in the glTF animation data are sparse, usually < 30 FPS, and may be even sparser if the author has made efforts to optimize the file for size. Most viewers want to render at >= 60 FPS, i.e. to render more “frames” than you have “keyframes.” This is accomplished with interpolation, and glTF defines three interpolation modes: STEP, LINEAR, or CUBICSPLINE. You can find an explanation of the animation data here in the glTF tutorials.

Once you’ve interpolated “keyframe” values to get a value for the current “frame”, it’s time to render. There are three basic types of animation: Translation/Rotation/Scale (TRS), Morph Targets, and Skinning. TRS is the simplest, and just requires updating the object matrix, however you are sending that to the vertex shader.