rparams | The parameters Unity uses to render the primitives. |
topology | Primitive topology (for example, triangles or lines). |
vertexCount | The number of vertices per instance. |
instanceCount | The number of instances to render. |
Renders non-indexed primitives with GPU instancing and a custom shader.
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: 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 } } }