wined3d: Add support for updating part of a compressed surface.

[Christof Sigel]

Thanks for the input, I really should have realised my approach was 
incorrect as soon as I saw that DXT textures are in blocks.
I'm not quite sure how to go about writing a test case, would I just 
have to create and update surface(s) and check that the resulting 
surface(s) have been updated correctly?

also, there is another patch coming that can be ignored (I missed some 
variable name changes that caused my patch to fail to compile), not sure 
why my mails are showing up late on the mailing list (I am subscribed).

Henri Verbeet wrote:
> 2008/9/5 Christof Sigel <christof.sigel at intenode.on.net>:
>> +                        /* since DXT compressed formats are specified in 4x4 pixel blocks devide pitch by 4 */
>> +                        int srcPitch=srcLockedRect.Pitch>>2;
>> +                        int destPitch=destLockedRect.Pitch>>2;
> 
> That will break with DXT1 surfaces. All the DXT formats are specified
> in 4x4 blocks, but for DXT1 a 4x4 block is 8 bytes, while for the
> other DXT formats a block is 16 bytes. This also has implications for
> how you should handle copying row by row, since each row is 4 pixels
> high. Strictly speaking you should also verify that the pitch exactly
> corresponds to the surface width before using the "single memcpy"
> path, since theory the surface layout in memory could look like this:
> 
> |<----width--->|
> |<-----------pitch------------>|
> xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> |--------------|xxxxxxxxxxxxxxxx
> |              |xxxxxxxxxxxxxxxx
> |              |xxxxxxxxxxxxxxxx
> |    surface   |xxxxxxxxxxxxxxxx
> |              |xxxxxxxxxxxxxxxx
> |              |xxxxxxxxxxxxxxxx
> |              |xxxxxxxxxxxxxxxx
> |--------------|xxxxxxxxxxxxxxxx
> xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> 
> In other words, for a DXT1 surface with height h, width w and pitch p,
> you should copy h/4 rows of w*2 bytes, where each row starts at
> pBits+p*row. For DXT2/3/4/5 you'd copy w*4 bytes for each row. A test
> for this code would be appreciated.
> 
>