# RenderPrimitives(in RenderParams, MeshTopology, int, int)

> Renders non-indexed primitives with GPU instancing and a custom shader.

## Definition

* **Type:** Method
* **Namespace:** [UnityEngine](/engine/6000.0/script-reference/unityengine.md)
* **Assembly:** UnityEngine.CoreModule

## RenderPrimitives(RenderParams, MeshTopology, int, int)

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

### Parameters

**** (\[RenderParams]\(/engine/6000.0/script-reference/unityengine/renderparams)): The parameters Unity uses to render the primitives.**** (\[MeshTopology]\(/engine/6000.0/script-reference/unityengine/meshtopology)): Primitive topology (for example, triangles or lines).**** (\[int]\(https\://learn.microsoft.com/dotnet/api/system.int32)): The number of vertices per instance.**** (\[int]\(https\://learn.microsoft.com/dotnet/api/system.int32)): 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](/engine/6000.0/script-reference/unityengine/graphics/renderprimitivesindexed.md).

The following example renders 10 instances of a Mesh using the function. The associated Material must use the below custom shader:

```csharp
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:

```csharp
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
        }
    }
}
```