# initializationValue The default value for vertex data for this attribute. ``` var initializationValue: vector_float4 { get set } ``` ## Discussion When you set the [`vertexDescriptor`](/documentation/ModelIO/MDLMesh/vertexDescriptor) property of a [`MDLMesh`](/documentation/ModelIO/MDLMesh) object, the mesh automatically formats its vertex buffers to match the new descriptor. If the vertex descriptor contains a vertex attribute that is not already present in the mesh, the mesh creates a new vertex buffer (or allocates space in an interleaved vertex buffer, if the vertex descriptor describes such) for the new attribute, and fills in per-vertex data for that attribute using this property’s value. Although this property’s type is `vector_float4`, Model I/O uses only the components of the vector that match the vertex attribute’s [`format`](/documentation/ModelIO/MDLVertexAttribute/format) property. For example, if you set this property’s value to the vector `{1, 2, 3, 4}` on a vertex attribute whose format is [`MDLVertexFormat.float2`](/documentation/ModelIO/MDLVertexFormat/float2), each vertex will be initialized with the value `{1, 2}`. The default initialization value is the vector `{0, 0, 0, 1}`. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)