prevents segfault when state trackers try to set default mask.
Other option would be to make this required only for drivers
supporting multisampling, but this seems more clean.
Only dummy implementations (for normal drivers) provided (no driver
supports multisampling yet neither).
compile tested only.
Should probably change the python surface_copy/fill functions
also into resource_copy/fill_region functions and adapt the code
using them.
The util blit functions change their interface (apart from some rename) too
(in particular util_blit_pixels now also takes a pipe_resource as the src blit
argument instead of a surface, as it might just call resource_copy_region).
Maybe the blit util code might need a bit more cleanup, it still doesn't feel
very clean. In particular it seems that util_blit_pixels_tex should probably
disappear, and I think it would be great if the code called by drivers for
blitting (u_blitter.c, which isn't really touched by this change) could somehow
be merged with the u_blit code.
Previously, surface_copy was said to allow overlapping blits, and it was
"optional". However, some state trackers actually assumed it is always present,
and quite some code (like in u_blit) assumed overlapping isn't allowed.
Hence, resource_copy_region (and in the same spirit, resource_fill_region) is
now mandatory, but overlapping blits are no longer allowed. A driver can plug
in the cpu fallback util_resource_copy_region if it does not want to provide its
own implementation, though this is not optimal.
due to popular request, use nr_samples parameter in is_format_supported()
instead of new is_msaa_supported() query.
This makes it easily possible to query if a format with a given sample count
is also supported not only as render target, but for sampler views (note that
texture sampling from multisampled resources isn't supported yet).
It is not quite how dx10 format msaa queries work, but we might need to revisit
format queries completely in the future anyway.
