# geometryShader GLSL source code for the program’s optional geometry shader. ``` var geometryShader: String? { get set } ``` ## Discussion A program’s geometry shader executes once for each geometric primitive (line or triangle) to be rendered. The geometry shader takes as input the vertex positions output by the vertex shader (or by the tessellation shader, if one is in use), and outputs new geometric primitives for rendering. Geometry shaders require macOS and OpenGL Core Profile. To use OpenGL Core Profile in a SceneKit view, set the view’s [`pixelFormat`](/documentation/SceneKit/SCNView/pixelFormat) property. Geometry shading is optional—to render without a geometry shader, set this property’s value to `nil` (the default). SceneKit compiles and links your shader program only when it is needed for rendering. To be notified of program compilation errors, provide a [`delegate`](/documentation/SceneKit/SCNProgram/delegate) object for the program. --- 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)