Simplest way of skeletal animation in openGL

Question

I am not interested in using easy libraries like assimp which will import collada files with ease to get skeleton animation done.

I wanna know what is the minimal requirement to get the animation done.

What I understand is that a bone is a 3*3 rotation matrix which is associated with each group of vertex.

We have to augment it with the model matrix to animate anything

How would I play a sequential animation with my existing bone system.

What's the workflow to process the bones. Sending bones through Uniform block is slow but I would consider doing it.

What's the simplest file format to store rig and animation data. Collada is unnecessarily advanced and complex.

Or how would I write my own file format for animation.

I am using blender to model and rig. How would I even manage to get an exporter for my format in blender

Answer 1

Those are 3 questions:

1. How to implement a simple skeletal animation in OpenGL
2. What is the simplest file format to store skeletal structure and animation data
3. How to import from Blender to OpenGL

I will focus on the main question and just add notes for the 2 others:

How to implement a simple skeletal animation in OpenGL

An simple skeletal require:

• A simple bone could be a transformation matrix. Which apply a rotation and translation.
• A bone apply to a set of vertexes
• A bone effect on a specific vertex is weighted between 0 and 1. To avoid strange effect on articulations.

A very simple way to solve that in OpenGL is:

• Every frame, update and save in an uniform vector each bones transformation matrix, ordered so a leaf is always after a root.
• Each vertex in the VBO contain, not only its position and normal, but also a list of weights of the size of the bone vector.
• In the vertex shader, for each bone, weight the bone matrix and apply it. So unrelated bones will multiply by the identity matrix, and relevant will have a real effect.
• Several optimizations are possible

Short answer about file formats:

There are plenty of file-formats which accept bones, and to suggest one or another depends mostly of your specific requirements. I suggest you to look for:

• Support bones, at the complexity you want.
• Is not over-complex neither missing important features.
• The format is documented and, ideally, standardized.

Blender native format is, however, generally not a good idea: the format is not formally defined, so it is difficult to implement an exporter (except by just copying the loading code).

Creating your own format is possible and quite easy: You may create a script in blender to export and load it in your application.

EDITED 1:

Requirement of data for a "correct" skeletal file format:

• Bone hierarchy
• Affected vertex per bone, or
• Bones influence range, or weight per vertex.
• Articulation axes, and angular limitations to every one
• Animation of bones:
  • Allows several animations (e.g. one for walking, another for jumping...)
  • Definition of bone movement per animation.
  • Timing for the animation.