[PATCH 3/4] wined3d: allow complex -> complex blits in arbfp blit_shader under special circumstances

[Roderick Colenbrander]

>> +        && (dst_usage & WINED3DUSAGE_RENDERTARGET))
> What is that condition for?

For a part it was meant to disable sysmem -> sysmem copies using the
arbfp blit_shader (but that should be done in general, so outside this
check). I wasn't sure whether dst_pool == D3DPOOL_DEFAULT would be
safe in general (sysmem->texture is but texture->texture might need
fbo_blit) hence the render_target restriction.

I could add something like this (as a separate patch of course):
if (dst_pool != default)
    return FALSE;

Further I can add the following condition to disallow texture->texture
blits, so that fbo_blit can handle them:
if (src_pool == default && dst_pool == default)
    return FALSE;
Perhaps at some point we might want to offer this for srgb texture
reloads but I don't know the finer details of that only saw some
comments in the code.

Roderick