Newb Question about UVs and Shader/performance

Unity Engine
1

Not sure if this is the appropriate thread to list. If not please guide me where to post. Thanks.

So, my question is…

I have been designing a scene (a town) which quickly added up set pass and batches. So, I started playing around in blender. I am relatively new to this. So my approaches have been

  1. Uv mapped everything nice and neatly desolved every possible edge and vert. Tried baking textures. Not much resolution. Very low vert and tri count… So I continued to think and experiment.

  2. Still Uv mapped nicely, and used tiled textures with geometry added to meshes. Resolution was amazing, vert and tri count a tid bit higher than before but nothing critical. Still quite a few set pass and batches though, to many for a mobile device. Around 19 per scene. Give or take a few.

  3. Pondered texture atlas theory and how to use it as a tiled texture concept. So, I skewed my mesh unwrappings, subdivided each quad to allow texture to fit nicely in sections. Then, unwrapped each quad
    and section individually to maintain an aspect ratio to the texture. Compiled a 1024x1024 texture containing all my 30 some textures for a single town. Loaded the texture map into blender and starting puzzling the pieces of UV together, over lapping and scaling to make it all look like a beautiful tiled texture, with acceptable resolution. Vert and Tri count is a tid bit higher than “2” but only by about 1-2k per entire camera view. OC will help this for sure. So no worries as of now…

So, this brought more questions to myself… Lightmapping…Uh Oh!

My question comes down to this… is there a more simplified version to “3” using a atlas… OR should I use a separate UV layout for lightmapping and continue “3”. I tested this with a quick flick of the mouse by baking a lightmap in blender (nothing fancy just a light baked onto the mesh with no material except plain white). Exported the mesh with two UVs saved as UV0 and UV1. Placed texture atlas into albedo, then in detail slot of standard shader switched to UV1 and dropped the light map. It worked. So… if there is no more simplified version of “3”… can someone help me in pointing me to information on accessing the secondary uv layout by script for a custom shader as I know standard is expensive for mobile.

I’m rookie at all this, I just tinker around in spare time. I have learned a bit from trial and error but more complex scripting kinda makes me dizzy. Any tips on any of the above and guidance is greatly appreciated. Thanks for reading!

2

Unity uses UV channel 2 for lightmapping by default. However, it generates its own layout (there is the option to preserve UV islands from pre-existing channel 2 on the mesh, but it will still shuffle them around), and it will only work with lightmaps rendered in Unity itself. So there is no easy way of using lightmaps rendered in other applications save for writing your own shader.