Let's assume we have a collection of working full-screen image effects that work with both multi-pass and SPSR. When SPSR was introduced, many shaders had to be modified to introduce the use of new macros like UnityStereoScreenSpaceUVAdjust to seamlessly support both XR rendering paths. The positive outcome of that change was the support for both multi-pass and SPSR using the same shader code, so it was just another abstraction layer to implement. Now, we are presented with another VR rendering path (Single Pass Instanced) which introduces a completely new set of macros to use across the shaders. So how is supposed we should support the new Single Pass Instanced in existing full-screen image effects? Specifically I'd like to know if the new APIs will gracefully work with SPSR (non-instanced) - or if not possible, what's the alternative to have full-screen image effects supporting all XR paths (duplicating packages/shaders?).