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Unity Engine

RenderPrimitives(in RenderParams, MeshTopology, int, int)

Renders non-indexed primitives with GPU instancing and a custom shader.
Read time 2 minutesLast updated 5 days ago

Definition

  • Type: Method
  • Namespace: UnityEngine
  • Assembly: UnityEngine.CoreModule

RenderPrimitives(RenderParams, MeshTopology, int, int)

public static void RenderPrimitives(in RenderParams rparams, MeshTopology topology, int vertexCount, int instanceCount = 1)

Parameters

rparams

RenderParams
The parameters Unity uses to render the primitives.

topology

MeshTopology
Primitive topology (for example, triangles or lines).

vertexCount

int
The number of vertices per instance.

instanceCount

int
The number of instances to render.

Remarks

Renders a given number of instances and primitives that have specific topology. This method requires custom shaders to fetch or calculate vertex data using the 
SV_VertexID
semantic. To access instance ID use 
SV_InstanceID
semantic.
Additional Resources: Graphics.RenderPrimitivesIndexed.
The following example renders 10 instances of a Mesh using the function. 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;    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);    }    void OnDestroy()    {        meshTriangles?.Dispose();        meshTriangles = null;        meshPositions?.Dispose();        meshPositions = 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("_StartIndex", (int)mesh.GetIndexStart(0));        rp.matProps.SetInt("_BaseVertexIndex", (int)mesh.GetBaseVertex(0));        rp.matProps.SetMatrix("_ObjectToWorld", Matrix4x4.Translate(new Vector3(-4.5f, 0, 0)));        rp.matProps.SetFloat("_NumInstances", 10.0f);        Graphics.RenderPrimitives(rp, MeshTopology.Triangles, (int)mesh.GetIndexCount(0), 10);    }}
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"            struct v2f            {                float4 pos : SV_POSITION;                float4 color : COLOR0;            };            StructuredBuffer<int> _Triangles;            StructuredBuffer<float3> _Positions;            uniform uint _StartIndex;            uniform uint _BaseVertexIndex;            uniform float4x4 _ObjectToWorld;            uniform float _NumInstances;            v2f vert(uint vertexID: SV_VertexID, uint instanceID : SV_InstanceID)            {                v2f o;                float3 pos = _Positions[_Triangles[vertexID + _StartIndex] + _BaseVertexIndex];                float4 wpos = mul(_ObjectToWorld, float4(pos + float3(instanceID, 0, 0), 1.0f));                o.pos = mul(UNITY_MATRIX_VP, wpos);                o.color = float4(instanceID / _NumInstances, 0.0f, 0.0f, 0.0f);                return o;            }            float4 frag(v2f i) : SV_Target            {                return i.color;            }            ENDCG        }    }}