batch-render-group
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BatchRendererGroup (or BRG) is an API that efficiently generates draw commands from C# and produces GPU-instancing draw calls.
DrawMeshInstanced 需要托管内存, 传入 TRS 数组
DrawMeshInstanced 需要自定义着色器
DrawMeshInstanced 每次绘制需要上传 GPU
BRG shader data model
the standard constant buffer (UnityPerMaterial)
custom, large GPU buffer (BRG raw buffer)
Shader Storage Buffer Object (SSBO, or byte address buffer)
The default BRG data layout is the structure of arrays (SoA) type
BRG metadata
Bits 0–30 define the offset of the property within the BRG raw buffer,
and bit 31 tells whether the property value is the same for all instances or the offset is the beginning of an array, with one value per instance.
两种 Buffer
BRG culling and visibility indices
BRG matrix format and buffer
SoA layout
allocate a similar buffer in system memory (CPU can process data at full speed in system memory).
Let’s call this second buffer a “shadow copy” of the GPU memory
When animation is done, we upload the shadow copy buffer to the GPU using the GraphicsBuffer.SetData API.
defined as follows
“unity_ObjectToWorld” property is an array starting at offset 0 of the BRG raw buffer
“unity_WorldToObject” property is an array starting at offset 153,600
“_BaseColor” property is an array, starting at offset 307,200
most GLES 3.0 devices can’t access SSBO during the vertex stage (i.e., the GL_MAX_VERTEX_SHADER_STORAGE_BLOCKS value is 0).
在 OpenGL 上用 UBO 替代 SSBO
A constant buffer can be any size, but only a small part of it (a window) is visible at any given time when the shader is running. The window size depends on the hardware and driver, but a widely accepted value is 16 KiB.
BatchRendererGroup.GetConstantBufferMaxWindowSize() API to get the correct BRG window size.
To generate all draw commands into the output BatchCullingOut struct
To use (or not) information provided in the BatchCullingContext read-only struct within your own culling code
A BRG draw command is almost a GPU DrawInstanced call.
