# Sandbox.VertexBuffer.AddTriangleIndex

```csharp
void AddTriangleIndex(int a, int b, int c)
```

Add a triangle by indices. This is relative to the top of the vertex buffer. So 0 is Vertex.Count.

### Parameters

- `a` (`int`)
- `b` (`int`)
- `c` (`int`)

### Exceptions

- `System.InvalidOperationException`: Thrown when [Sandbox.VertexBuffer.Indexed](/api/Sandbox.VertexBuffer/Indexed) is false.

Declared in [Sandbox.VertexBuffer](/api/Sandbox.VertexBuffer).
Assembly: `Sandbox.Engine`.