# geometry Use this entry point to deform a geometry’s surface or alter its vertex attributes. ``` static let geometry: SCNShaderModifierEntryPoint ``` ## Discussion Shader modifiers for this entry point execute in the vertex processing stage. The geometry entry point declares the following structure: ```objc struct SCNShaderGeometry { vec3 position; vec3 normal; vec4 tangent; vec2 texcoords[kSCNTexcoordCount]; } _geometry; ``` Your shader modifier reads from this structure and writes new values to the same structure to alter the geometric properties of each vertex in a geometry. The `position`, `normal`, and `tangent` fields are expressed in model space. You can use SceneKit’s uniforms (such as `u_modelViewTransform`) to operate in a different coordinate space, but you must convert back to model space before writing results. The `kSCNTexcoordCount` variable is a constant integer corresponding to the geometry’s number of texture coordinate sources. Each set of coordinates in the `texcoords` field contains raw values from the geometry—SceneKit applies the [`contentsTransform`](/documentation/SceneKit/SCNMaterialProperty/contentsTransform) transformation (if any) after the geometry shader modifier completes. The below shader modifier produces an animated sinusoidal deformation: ```objc uniform float Amplitude = 0.1; _geometry.position += _geometry.normal * (Amplitude*_geometry.position.y*_geometry.position.x) * sin(1.0 * u_time); ``` --- 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)