Task (REQUIRED):
Right now we export tangents from modelc as vec3s and then derive bitangents from the normal and the tangent, meaning we have no way of knowing if the tangent coordinate system is correct or not. A typical solution, if we don't want to export bitangents, is to pack the handedness direction in the .w component of the tangent vector, which can then be used to multiple the bitangent vector with after the derivation in the shader. Blender exports tangents in this way (and I think most do), so it should be a simple improvement.

Expected outcome (REQUIRED):
Describe the expected outcome of the task (new issue, documentation, code change etc)