Version: 2021.3
LanguageEnglish
  • C#

Graphics.RenderPrimitivesIndirect

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Declaration

public static void RenderPrimitivesIndirect(ref RenderParams rparams, MeshTopology topology, GraphicsBuffer commandBuffer, int commandCount = 1, int startCommand = 0);

Parameters

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.

Description

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: See Also: 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 } } }