---
title: "setVertexAmplificationCount:viewMappings:"
framework: metal
role: symbol
role_heading: Instance Method
path: "metal/mtl4rendercommandencoder/setvertexamplificationcount:viewmappings:"
---

# setVertexAmplificationCount:viewMappings:

Sets the vertex amplification count and its view mapping for each amplification ID.

## Declaration

```occ
- (void) setVertexAmplificationCount:(NSUInteger) count viewMappings:(const MTLVertexAmplificationViewMapping *) viewMappings;
```

## Parameters

- `count`: The number of outputs to create. The maximum value is 2.
- `viewMappings`: Array of doc://com.apple.metal/documentation/Metal/MTLVertexAmplificationViewMapping instances. Each instance provides per-output offsets to a specific render target and viewport.

## Discussion

Discussion Each view mapping element describes how to route the corresponding amplification ID to a specific viewport and render target array index by using offsets from the base array index provided by the [[ render_target_array_index ]] and/or [[ viewport_array_index ]] output attributes in the vertex shader. This allows Metal to route each amplified vertex to a different [[ render_target_array_index ]] and [[ viewport_array_index ]], even though you can’t directly amplify these attributes.