You should know it before tracing display/graphic codes

General meanings of some API in Android frameworks:

1. graphic buffer manipulation

I. dequeue buffer: ask the buffer manager to release a buffer for modifying in the near future.

II. lock buffer: lock a buffer. It's essential before modifying it.

III. queue buffer: call it when modification is done. This will unlock and post the buffer.

IV. cancel buffer: cancel a buffer which was dequeued. Return it to the buffer manager.

not finished.