Considering modern OpenGL ( 3.x, 4.x, ES 2 and 3, WebGL ) and modern GLSL, what is the status of the support for quaternions vs the support for matrices ?
I'm finding more and more modern algorithms and papers that most of the times completely bypass matrix representations and only speak in terms of quaternions, especially the ones about lighting, but I still have to find any trace of quaternions inside OpenGL or any OpenGL ARB extension.
What's the status of quaternions for this Khronos standard ?
Nonexistent, you can pass them into the shaders as a vec4 but you'll have to implement the application of the quat rotation to a vector yourself.
Besides that you still need to pass in a vec3 translation and the projection parameters.
Most of the time it's faster to create the equivalent matrix from the quat plus translation pls projection and pass in the mat4 instead. Largely because multiplying a mat4 with a vector is faster (and better optimized in hardware) than applying the same rotation as a quat, and if you do enough of it the mat4 wins in speed even accounting the effort needed to transform the quat into the mat4 representation.