A container for vertex data forming part of the definition for a three-dimensional object, or geometry.
SDKs
- iOS 8.0+
- macOS 10.8+
- Mac Catalyst 13.0+
- tvOS 9.0+
- watchOS 2.0+
Framework
- Scene
Kit
Declaration
class SCNGeometrySource : NSObject
Overview
You use geometry sources together with SCNGeometry
objects to define custom SCNGeometry
objects or to inspect the data that composes an existing geometry.
You create a custom geometry using a three-step process:
Create one or more
SCNGeometry
objects containing vertex data. Each geometry source defines an attribute, or semantic, of the vertices it describes. You must provide at least one geometry source, using theSource vertex
semantic, to create a custom geometry; typically you also provide geometry sources for surface normals and texture coordinates.Create at least one
SCNGeometry
object, containing an array of indices identifying vertices in the geometry sources and describing the drawing primitive that SceneKit uses to connect the vertices when rendering the geometry.Element Create an
SCNGeometry
instance from the geometry sources and geometry elements.
Interleaving Vertex Data
Because most geometries use more than one geometry source and the GPU typically uses data from multiple sources together, you can achieve better rendering performance for custom geometries by interleaving the vertex data for multiple semantics in the same array.
To do this, first create an array where each element contains values for multiple semantics for the same vertex. Next, create an NSData
object from that array, and create each geometry source from that data using the offset
and stride
parameters to specify where the values for each semantic can be found in the array. To make specifying the sizes and locations of vectors more convenient, you can define your own data structure for vertices and use the sizeof
(and, in Objective-C, offsetof
) functions, as shown in Listing 1.
Creating multiple geometry sources from interleaved data
typedef struct {
float x, y, z; // position
float nx, ny, nz; // normal
float s, t; // texture coordinates
} MyVertex;
MyVertex vertices[VERTEX_COUNT] = { /* ... vertex data ... */ };
NSData *data = [NSData dataWithBytes:vertices length:sizeof(vertices)];
SCNGeometrySource *vertexSource, *normalSource, *tcoordSource;
vertexSource = [SCNGeometrySource geometrySourceWithData:data
semantic:SCNGeometrySourceSemanticVertex
vectorCount:VERTEX_COUNT
floatComponents:YES
componentsPerVector:3 // x, y, z
bytesPerComponent:sizeof(float)
dataOffset:offsetof(MyVertex, x)
dataStride:sizeof(MyVertex)];
normalSource = [SCNGeometrySource geometrySourceWithData:data
semantic:SCNGeometrySourceSemanticNormal
vectorCount:VERTEX_COUNT
floatComponents:YES
componentsPerVector:3 // nx, ny, nz
bytesPerComponent:sizeof(float)
dataOffset:offsetof(MyVertex, nx)
dataStride:sizeof(MyVertex)];
tcoordSource = [SCNGeometrySource geometrySourceWithData:data
semantic:SCNGeometrySourceSemanticTexcoord
vectorCount:VERTEX_COUNT
floatComponents:YES
componentsPerVector:2 // s, t
bytesPerComponent:sizeof(float)
dataOffset:offsetof(MyVertex, s)
dataStride:sizeof(MyVertex)];