I have two sets of lightmaps for my scene and would like to blend them interactively. I have done some research into how Unity handles lightmaps internally, and it seems that multiple lightmaps cannot be accessed within the same shader due to the way they are exposed to shaders (unity_Lightmap and unity_LightmapST).
Is there a workaround that would allow me to blend between multiple lightmaps in a shader?
If you are willing to only use single lightmaps and both sets use the same number of lightmaps, then yes. What you would do is bake two sets of single lightmaps. Then you’d modify LightmapSettings.Lightmaps and put one lightmap into each LightmapNear and the other into each LightmapFar. Finally, you have your shader do the lightmap blending. Of course, you’d need to use that shader on all lightmapped objects or you might see the wrong lightmap data.
Alternatively, lightmaps are just textures, so you could bind them in yourself and use whatever Unity shader macros to unpack the data for you.