init(buffer:vertexFormat:semantic:vertexCount:dataOffset:dataStride:)

Declaration

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 Mtlvertexformat 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 MTLBuffer object for use with a geometry source, use the device property of the SceneKit view (or other renderer) responsible for drawing your scene.

// Create and fill a buffer.
id <MTLDevice> 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:).

- (void)renderer:(id <SCNSceneRenderer>)aRenderer willRenderScene:(SCNScene *)scene atTime:(NSTimeInterval)time {
     // Get a command buffer and compute encoder from the view (or other renderer).
     id<MTLCommandBuffer> myCommandBuffer = [aRenderer.commandQueue commandBuffer];
     id<MTLComputeCommandEncoder> 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];
}