# init(buffer:vertexFormat:semantic:vertexCount:dataOffset:dataStride:) Creates a geometry source whose vertex data resides in the specified Metal buffer, allowing modification through a Metal compute shader. ``` convenience init(buffer: any MTLBuffer, vertexFormat: MTLVertexFormat, semantic: SCNGeometrySource.Semantic, vertexCount: Int, dataOffset offset: Int, dataStride stride: Int) ``` ## Parameters `buffer` A Metal buffer containing per-vertex data for the geometry source. `vertexFormat` The type of per-vertex data in the buffer. A value defines the number of components for each vector in the geometry source and the data type and size of each component. `semantic` The semantic value (or attribute) that the geometry source describes for each vertex. See Geometry Semantic Identifiers for available values. `vertexCount` The number of vertices in the geometry source. `offset` The offset, in bytes, from the beginning of the data to the first vector component to be used in the geometry source. `stride` The number of bytes from each vector to the next in the data. ## Return Value A new geometry source object. ## Discussion Use this method to create a geometry source whose underlying data can be modified at render time by a Metal compute shader running on the GPU. To create a object for use with a geometry source, use the [`device`](/documentation/SceneKit/SCNSceneRenderer/device) property of the SceneKit view (or other renderer) responsible for drawing your scene. ```objc // Create and fill a buffer. id device = self.scnView.device; self.geometryBuffer = [device newBufferWithBytes:myData length:myLength options:myOptions]; // Create a geometry source from the buffer. SCNGeometrySource *source = [SCNGeometrySource geometrySourceWithBuffer:buffer vertexFormat:myVertexFormat semantic:SCNGeometrySourceSemanticVertex vertexCount:myVertexCount dataOffset:0 dataStride:0]; ``` Then, to modify the buffer’s contents at render time, implement a scene renderer delegate and schedule a compute command encoder during a render delegate method such as [`renderer(_:willRenderScene:atTime:)`](/documentation/SceneKit/SCNSceneRendererDelegate/renderer(_:willRenderScene:atTime:)). ```objc - (void)renderer:(id )aRenderer willRenderScene:(SCNScene *)scene atTime:(NSTimeInterval)time { // Get a command buffer and compute encoder from the view (or other renderer). id myCommandBuffer = [aRenderer.commandQueue commandBuffer]; id myComputeEncoder = [myCommandBuffer computeCommandEncoder]; // Configure the compute command encoder. // (Note pipeline state is preconfigured outside of the render loop.) [myComputeEncoder setComputePipelineState:self.pipelineState]; [myComputeEncoder setBuffer:self.geometryBuffer offset:0 atIndex:0]; // Schedule the compute command and commit the command buffer. [myComputeEncoder dispatchThreadgroups:myThreadgroupCount threadsPerThreadgroup:myThreadCount]; [myComputeEncoder endEncoding]; [myCommandBuffer commit]; } ``` > Note: > Geometry sources backed by a Metal buffer are available only with SceneKit views (or other renderers) whose ``doc://com.apple.scenekit/documentation/SceneKit/SCNSceneRenderer/renderingAPI`` property is ``doc://com.apple.scenekit/documentation/SceneKit/SCNRenderingAPI/metal``. > > Metal commands that modify the buffer’s contents must be enqueued from within one of the render loop methods defined in the ``doc://com.apple.scenekit/documentation/SceneKit/SCNSceneRendererDelegate`` protocol. The result of attempting to modify a buffer at any other time is undefined. --- 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)