[ddraw] asynchronous screen updates

[Lionel Ulmer]

> Here are my changes:
> 
> - User_add_dirty_rect is now an asynchronous equivalent of 
> User_copy_to_screen. It adds the rectangle to the list of dirty rectangles 
> and signal the update thread that there is some work to do.
> - update thread calls User_get_dirty_rect to iterate over the list of dirty 
> rectangles
> - current "naïve" algoritm keeps only one rectangle which is a union of all 
> dirty rectangles, so it tends to redraw too much, but better algoritms may be 
> implemented
> - removed now unused lastlockrect variable, and the code which updates it
> 
> I attached the patch for your reviews, comments, suggestions.

The only comment I have on the patch is that you are using the rectangle
from the 'User_DirectDrawSurface_unlock_update' code. The big problem here
is that for old DirectX versions (versions 1 to 3), the lock rectangle was
not repeated in the Unlock call (it was only present in the Lock code).

So, basically, you will always force a full redraw for these old DirectX
versions. So, the best would be to add the dirty rectangles in the Lock
calls (if we are not in READONLY mode).

A part from that, the patch looks nice.

Same comments as in my other mails about contributors :-)

         Lionel

PS: all these dirty region handling should be factorized as I did the same
    kind of hacks in the D3D code to speed up transfer between 2D and 3D
    buffers.

-- 
		 Lionel Ulmer - http://www.bbrox.org/