Simplifying things a little, I have an Effect class which is responsible for how to draw something, and amongst other things holds the vertex shader to use. I also have a Element class which holds the geometry to draw amongst other things (vertex buffer, index buffer etc).
The problem is that only my Element class knows about the format of the vertex buffers if uses so it's really the only object that can create and set the input layout, However in order to do this it needs to know which vertex shader is being used for that draw call, and in fact needs to create a different input layout for each shader that can be used to draw it, as well as to know at run time which shader is being used so it can select which input layout is the appropriate one.
I can make my Element object cache the ID3D11InputLayout in a map indexed on vertex structure type, and vertex shader type, and share that map between all of the elements rather than create the input layout each time it's asked to draw something (which I suspect would be horribly inefficient anyway...) but that just seems inelegant and mixes together the responsibilities for the Effect and the Element far too much.
So how do people handle selecting which input layout to use, creating the ID3D11InputLayout objects, and so on? Is there something I'm missing, or is my overall design flawed and could be altered?
Thanks for any suggestions
