| index | Index of the random write target in the shader. |
| uav | Buffer or texture to set as the write target. |
| preserveCounterValue | Whether to leave the append/consume counter value unchanged. |
Set random write target for Shader Model 4.5 level pixel shaders.
Shader Model 4.5 and above level pixel shaders can write into arbitrary locations of some textures and buffers, called "unordered access views" (UAV) in UsingDX11GL3Features. These "random write" targets are set similarly to how multiple render targets are set. You can either use a RenderTexture with enableRandomWrite flag set, or a ComputeBuffer as target.
The UAV indexing varies a bit between different platforms. On DX11 the first valid UAV index is the number of active render targets. So the common case of single render target the UAV indexing will start from 1. Platforms using automatically translated HLSL shaders will match this behaviour. However, with hand-written GLSL shaders the indexes will match the bindings. On PS4 the indexing starts always from 1 to match the most common case.
When setting a ComputeBuffer, the preserveCounterValue parameter indicates whether to leave the counter value unchanged, or reset it to 0 (the default behaviour).
The targets stay set until you manually clear them with ClearRandomWriteTargets. It is best practice to call ClearRandomWriteTargets after your rendering is complete. If you do not do this, rendering issues can occur and some built-in Unity rendering passes may crash.
Additional resources: RenderTexture.enableRandomWrite, ComputeBuffer, ComputeBuffer.SetCounterValue, UsingDX11GL3Features.