[Mesa-dev] [PATCH V2 00/17] Newbie Project : Enable ARB_map_buffer_alignment in all drivers

[Ian Romanick]

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On 12/03/2013 10:44 AM, Eric Anholt wrote:
> Siavash Eliasi <siavashserver at gmail.com> writes:
> 
>> Hello, this is V2 series of patches to accomplish *Enable 
>> ARB_map_buffer_alignment in all drivers* newbie project suggested
>> by Ian Romanick.
> 
> I think there's a piece missing to this, which is this bit of spec
> text:
> 
> "If no error occurs, the pointer value returned by MapBufferRange
> must reflect an allocation aligned to the value of
> MIN_MAP_BUFFER_ALIGNMENT basic machine units.  Subtracting <offset>
> basic machine units from the returned pointer will always produce a
> multiple of the value of MIN_MAP_BUFFER_ALIGNMENT."
> 
> In i965's intel_bufferobj_map_range, range_map_bo or
> range_map_buffer mappings won't have that alignment.

Yeah... I had forgotten about that when I originally posted the
project.  There are a couple ways we could handle it.  The one that
occurred to me first is to modify _mesa_MapBufferRange to only call
ctx->Driver.MapBufferRange with a properly aligned offset (and do the
fix-up on the pointer before storing it in gl_buffer_object::Pointer).
 We don't have to worry about gl_buffer_object::Offset being rounded
because, as far as I can tell, it's not visible to applications.  We'd
just have to make sure that each driver's UnmapBuffer implementation
only uses Offset and not Pointer.

Does that sound sensible?

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