Locking Our Buffers
The locking mechanism seems to be one of the most misunderstood calls in Direct3D, particularly in Managed DirectX. How to do the locks, and do them fast seems to be a particularly tough question for people to grasp.
Before we get to that, though, what exactly is “locking” the buffer? It is simply the act of allowing your CPU to access a range of data in your resource. Since you cannot talk directly to the graphics hardware, there needs to be a way to allow you to manipulate vertex data from your application, and the locking mechanism is it. Look at the various lock overloads that exist for our vertex and index buffers (they take the same parameters):
public System.Array Lock ( System.Int32 offsetToLock , Microsoft.DirectX.Direct3D.LockFlags ...