Passing a property to a Shader without breaking batching

In the case you have multiple GameObjects with the same custom Shader:
How can I preserve batching if I pass a dynamic property to the material of one of those objects (for example doing something like renderer.material.SetFloat( "_MyPropertyName", 2f ) ), without using sharedMaterial.

Thanks!

 

Short version: You can't.

Longer version: Unity supposedly has some utilities with MaterialPropertyBlock that it uses internally for reducing draw calls for objects placed via the terrain painting... but this doesn't actually reduce the draw counts or allow batching in the general case and it remains a bit of a mystery what it's doing internally.

What you can do is manually batch objects and store the unique parameters in each object's vertex colors or extra UV channels. If this is something that needs to change frequently this obviously doesn't work well, but it's the option we've got.

 

Thanks bgolus, could you give me an example using the extra UV channels? Also how can I make sure those are not used internally by Unity?

 

UV1 (aka TEXCOORD0) is usually used for texturing, and UV2 gets used by Unity if the object is using light maps. UV3 and UV4 (TEXCOORD2 and TEXCOORD3) are almost never used.

So you have a mesh, you make a copy of that mesh and use SetUVs(3, someVectorList) to set the values. Combine multiple meshes manually using CombineMeshes. Then in the shader get TEXCOORD2 in the vertex shader and pass them onto the pixel shader.

http://docs.unity3d.com/ScriptReference/Mesh.SetUVs.html
http://docs.unity3d.com/ScriptReference/Mesh.CombineMeshes.html
http://docs.unity3d.com/Manual/SL-VertexProgramInputs.html

When using SetUVs you'll actually need to make a list with as many elements as the mesh has vertices and set them all to the values you want the shader to read. If you need more than 4 values you can use UV4 or do float packing. I think there's even some utility functions in the Unity cginc files for packing 4 lower precision floats into 1 float value (like a color).

 

Thanks! Would this work only with a Mesh Renderer or also with a Sprite Renderer?

 

Mesh only. Sprite renderer doesn't have direct access to the UVs. For that I think you can only reuse the sprite color as alternate parameters. It's not that the sprite renderer is incapable of this, it just doesn't give you access as is. Internally it's working almost identically to the method I described, just generating quad meshes instead of copying an existing mesh and combining.

 

Ok thank you very much! I am wondering if it's worth not using 2D Sprite and go directly to Mesh Renderer just for this.

 

I know this is a really old post, but did anything come out of this?

 

The MaterialPropertyBlock they talk about have been a thing since 2016.
https://thomasmountainborn.com/2016/05/25/materialpropertyblocks/
https://docs.unity3d.com/ScriptReference/MaterialPropertyBlock.html

Though for URP/HDRP I believe it is recommended to use the CBUFFER for your per-material changing values to utilize the SRPBatcher instead.