rparams | The parameters Unity uses to render the primitives. |
topology | Primitive topology (for example, triangles or lines). |
commandBuffer | A command buffer that provides rendering command arguments (see IndirectDrawArgs). |
commandCount | The number of rendering commands to execute in the commandBuffer . |
startCommand | The first command to execute in the commandBuffer . |
Renders primitives with GPU instancing and a custom shader using rendering command arguments from commandBuffer
.
This function provides a way to control rendering command arguments from GPU to render a given number of primitives and instances. Use RenderParams.worldBounds
to define bounds to cull and sort the geometry rendered with the method as a single entity.
This function only works on platforms that support compute shaders.
Add the following lines in the pass section of a shader to access command, instance and vertex ID's as specified in UnityIndirect.cginc:
Additional resources: RenderMeshIndirect.
#define UNITY_INDIRECT_DRAW_ARGS IndirectDrawArgs #include "UnityIndirect.cginc"
Add the following line to the beginning of a shader function to setup the ID access functions:
InitIndirectDrawArgs(0); // pass SV_DrawID semantic value here for multi-draw support
The following example executes two indirect rendering commands. Each command renders 10 Mesh instances. The associated Material must use the below custom shader:
using UnityEngine;
public class ExampleClass : MonoBehaviour { public Material material; public Mesh mesh;
GraphicsBuffer meshTriangles; GraphicsBuffer meshPositions; GraphicsBuffer commandBuf; GraphicsBuffer.IndirectDrawArgs[] commandData; const int commandCount = 2;
void Start() { // note: remember to check "Read/Write" on the mesh asset to get access to the geometry data meshTriangles = new GraphicsBuffer(GraphicsBuffer.Target.Structured, mesh.triangles.Length, sizeof(int)); meshTriangles.SetData(mesh.triangles); meshPositions = new GraphicsBuffer(GraphicsBuffer.Target.Structured, mesh.vertices.Length, 3 * sizeof(float)); meshPositions.SetData(mesh.vertices); commandBuf = new GraphicsBuffer(GraphicsBuffer.Target.IndirectArguments, commandCount, GraphicsBuffer.IndirectDrawArgs.size); commandData = new GraphicsBuffer.IndirectDrawArgs[commandCount]; }
void OnDestroy() { meshTriangles?.Dispose(); meshTriangles = null; meshPositions?.Dispose(); meshPositions = null; commandBuf?.Dispose(); commandBuf = null; }
void Update() { RenderParams rp = new RenderParams(material); rp.worldBounds = new Bounds(Vector3.zero, 10000*Vector3.one); // use tighter bounds rp.matProps = new MaterialPropertyBlock(); rp.matProps.SetBuffer("_Triangles", meshTriangles); rp.matProps.SetBuffer("_Positions", meshPositions); rp.matProps.SetInt("_BaseVertexIndex", (int)mesh.GetBaseVertex(0)); rp.matProps.SetMatrix("_ObjectToWorld", Matrix4x4.Translate(new Vector3(-4.5f, 0, 0))); commandData[0].vertexCountPerInstance = mesh.GetIndexCount(0); commandData[0].instanceCount = 10; commandData[1].vertexCountPerInstance = mesh.GetIndexCount(0); commandData[1].instanceCount = 10; commandBuf.SetData(commandData); Graphics.RenderPrimitivesIndirect(rp, MeshTopology.Triangles, commandBuf, commandCount); } }
Use the following example shader with the above C# example code:
Shader "ExampleShader" { SubShader { Pass { CGPROGRAM #pragma vertex vert #pragma fragment frag
#include "UnityCG.cginc" #define UNITY_INDIRECT_DRAW_ARGS IndirectDrawArgs #include "UnityIndirect.cginc"
struct v2f { float4 pos : SV_POSITION; float4 color : COLOR0; };
StructuredBuffer<int> _Triangles; StructuredBuffer<float3> _Positions; uniform uint _BaseVertexIndex; uniform float4x4 _ObjectToWorld;
v2f vert(uint svVertexID: SV_VertexID, uint svInstanceID : SV_InstanceID) { InitIndirectDrawArgs(0); v2f o; uint cmdID = GetCommandID(0); uint instanceID = GetIndirectInstanceID(svInstanceID); float3 pos = _Positions[_Triangles[GetIndirectVertexID(svVertexID)] + _BaseVertexIndex]; float4 wpos = mul(_ObjectToWorld, float4(pos + float3(instanceID, cmdID, 0.0f), 1.0f)); o.pos = mul(UNITY_MATRIX_VP, wpos); o.color = float4(cmdID & 1 ? 0.0f : 1.0f, cmdID & 1 ? 1.0f : 0.0f, instanceID / float(GetIndirectInstanceCount()), 0.0f); return o; }
float4 frag(v2f i) : SV_Target { return i.color; } ENDCG } } }