Official New BatchRendererGroup API for 2022.1

Apologies for the slow reply, I was on vacation when this post was made.

BatchRendererGroup itself does not currently automatically provide correct lightmaps, light probes, or reflection probes to rendered instances. Instead, the responsibility is on the BRG user (such as the Entities Graphics package) and the active SRP to handle these in the following manner:

• Lightmaps are expected to be provided manually in texture arrays. Normal Unity lightmaps are not texture arrays, and as such switching them requires breaking up draw calls. In addition, BatchRendererGroup does not currently have enough information available CPU side to figure out which instances are using which lightmaps. The Entities Graphics package, for example, manually packs lightmaps in arrays, so instances that are using several lightmaps can be rendered together in a single draw (other batching considerations permitting), and then sets up the unity_LightmapIndex property to contain the correct texture array index to use for each instance.
• Light probes are expected to be provided by the BRG user (or handled automatically by the SRP, but as far as I know this would require a custom SRP). BRG does not currently always have the necessary instance position information available to interpolate light probes, and even if it did, it would not be able to efficiently cache the results. The Entities Graphics package evaluates interpolated light probe coefficients using LightProbes.CalculateInterpolatedLightAndOcclusionProbes and overrides the unity_SHCoefficients property to contain the interpolated values. This interpolation is only done when the positions change, so the results will be reused if the entities don't move.
• Reflection probes currently rely completely on the SRP, which means that they will work in HDRP, or when using URP Forward+ (which evaluates reflection probes in screen space). Other URP modes do not currently support reflection probes when BRG is used.

BRG itself requires support for instanced rendering and shader integer operations, and it should work on GLES 3.0 and up. On GLES it will use UBOs instead of SSBOs, as SSBOs from vertex shaders are not universally supported on GLES. However, the GPU performance can greatly depend on the device, as many low end Android devices are not favorable towards instanced rendering in general, due to instance properties becoming "varying" values instead of "uniform" values.

The Entities Graphics package additionally requires compute shader support, but that is not a requirement for custom BRG usage.

Currently, Unity does not have a mechanism to configure how shaders are compiled, so there is no built in way to configure this. However, it is possible to use a locally modified package and comment out properties that you know you don't need. In addition, Shader Graphs provide a way to configure which properties are to be DOTS instanced on a per property basis, without requiring package modifications.

In general, customizing the package would also allow you to simplify or change how other pieces of the data are loaded. For these kinds of custom optimizations, you would be able to arrange things exactly according to what your game needs, and you would not be restricted by having to support a very wide variety of configurations.

If you are willing to write custom shaders, it should be possible to highly customize the data with the current BatchRendererGroup API in 2022.3. BatchRendererGroup itself does not really mandate a particular way of loading data, it just provides you a mechanism to efficiently issue instanced draws that have certain buffer bindings set up (the per batch SSBO, and the metadata UBOs with the metadata values for that batch). Unity shaders all use the documented convention how these are used to load instance properties, but a custom shader can do anything it wants with them (and could also use other globally bound textures or SSBOs).

Currently, you still need to split things by Mesh. Procedural support is something that we have been looking at, but is not available in the current version. However, on most platforms, switching Meshes should be relatively fast, cheaper than switching Materials.

 

Many people are talking about mobile development with BRG in this thread. So I thought it might be good to give more visibility to the new "Advanced DOTS Instanced properties usage" section in the BatchRendererGroup manual https://docs.unity3d.com/Manual/dots-instancing-shaders.html

It's available with 2023.2+ and got backported to 2022 LTS. It's basically giving more control over the way material properties are loaded and can lead to significant performance improvements on low-end platforms when using stock shaders like URP/Lit.

Especially, if you do not use instanced material properties at all, I would recommand looking into the shader define UNITY_DOTS_INSTANCED_PROP_OVERRIDE_DISABLED_BY_DEFAULT. On Quest 2, I was able to get a 15% reduction of the total GPU frame time on some basic scenes by enabling it.

Note that ShaderGraph shaders are not impacted by this define. They are already fast in this regard and doing the right thing by default.