support the default renderer

[KrabCode]

draw gradients and all the other shader stuff on the CPU if renderer == default, make a new class to handle all the processing interactions that are changed by this and allow gradient callers to depend on this new renderer agnostic abstraction

maybe show a warning that it's inefficient at startup? don't over-optimize the efficiency, dynamic gradients on the CPU will always be a workaround, just make it work somewhat (for a start)