How to access vertex of geometry? about gltfkit2 HOT 5 CLOSED

@interface GLTFPrimitive (VertexPositionAccess)
- (NSData *_Nullable)copyPackedVertexPositions;
@end

@implementation GLTFPrimitive (VertexPositionAccess)

- (NSData *)copyPackedVertexPositions {
    GLTFAccessor *positionAccessor = self.attributes[GLTFAttributeSemanticPosition];
    if (positionAccessor == nil) {
        return nil; // No position data, because the primitive didn't contain a position accessor
    }
    const void *sourceBufferBase = positionAccessor.bufferView.buffer.data.bytes;
    const void *sourceBase = sourceBufferBase + positionAccessor.offset + positionAccessor.bufferView.offset;
    if (sourceBase == NULL) {
        return nil; // No position data, because buffer view or buffer is NULL, or because the buffer contains no data
    }
    NSInteger vertexCount = positionAccessor.count;
    NSInteger destinationStride = sizeof(float) * 3;
    NSInteger bufferLength = destinationStride * vertexCount;
    NSInteger sourceStride = positionAccessor.bufferView.stride;
    if (sourceStride == 0) {
        sourceStride = destinationStride;
    }
    if (sourceStride == destinationStride) {
        // Existing data is already packed; just return a data object that acts as a view on it
        return [NSData dataWithBytesNoCopy:(void *)sourceBase length:bufferLength freeWhenDone:NO];
    } else {
        // Existing data is *not* packed; we need to copy it element by element
        void *packedBuffer = malloc(bufferLength);
        for (int i = 0; i < vertexCount; ++i) {
            const void *sourcePtr = sourceBase + i * sourceStride;
            void *destPtr = packedBuffer + i * destinationStride;
            memcpy(destPtr, sourcePtr, destinationStride);
        }
        return [NSData dataWithBytesNoCopy:packedBuffer length:bufferLength freeWhenDone:YES];
    }
}

@end