[Mesa-dev] RFC: array textures in gallium and assorted cleanups

[Roland Scheidegger]

On 10.06.2010 20:32, Roland Scheidegger wrote:
> On 10.06.2010 17:12, Keith Whitwell wrote:
>> On Thu, 2010-06-10 at 07:29 -0700, Brian Paul wrote:
>>> Keith Whitwell wrote:
>>>> On Thu, 2010-06-10 at 07:08 -0700, Roland Scheidegger wrote:
>>>>> On 10.06.2010 11:30, Keith Whitwell wrote:
>>>>>> On Thu, 2010-06-03 at 13:26 -0700, Roland Scheidegger wrote:
>>>>>>> Hi,
>>>>>>>
>>>>>>> I've created a new branch gallium-array-textures which has some more
>>>>>>> interface changes, this time to support array textures basically.
>>>>>>> Nothing has been adapted to these changes yet (I'll do that it should be
>>>>>>> mostly trivial as long as array textures aren't actually supported by
>>>>>>> the driver or even mesa state tracker), but now would be a good time if
>>>>>>> you have some comments for the proposed interface changes.
>>>>>>>
>>>>>>> Roland
>>>>>> Roland,
>>>>>>
>>>>>> This looks great!
>>>>>>
>>>>>> Couple of comments -- you're now using the term "layer" in various
>>>>>> places, but there is no strong definition of what that means - except in
>>>>>> the patch comment, which isn't useful once the patch is committed.  Can
>>>>>> you define this term somewhere in the documentation?
>>>>> Ok will do.
>>>>>
>>>>>> Also, there are a couple of things that look like typos in the interface
>>>>>> change diff, but I'm sure you'll find those the first time you try to
>>>>>> compile this.  eg:
>>>>>>
>>>>>>     void (*resource_copy_region)(struct pipe_context *pipe,
>>>>>>                                  struct pipe_resource *dst,
>>>>>> -                                struct pipe_subresource subdst,
>>>>>> +                                unsigned level,
>>>>>>                                  unsigned dstx, unsigned dsty, unsigned dstz,
>>>>>>                                  struct pipe_resource *src,
>>>>>> -                                struct pipe_subresource subsrc,
>>>>>> -                                unsigned srcx, unsigned srcy, unsigned srcz,
>>>>>> -                                unsigned width, unsigned height);
>>>>>> +                                unsigned level,
>>>>>> +                                const struct pipe_box *);
>>>>>>  
>>>>>> It seems like you end up with two parameters named "level" ??
>>>>> Yes, I had already fixed this locally.
>>>>> create_surface also had a bug (still got passed pipe_screen instead of
>>>>> pipe_context since it moved to context), as well as I need to store the
>>>>> context itself in pipe_surface (much like pipe_sampler_view does).
>>>>> That actually was a bit non-trivial since some state trackers don't
>>>>> really have a context handy when they called the former
>>>>> get_tex_surface() (glx, wgl and so on statetrackers not the rendering
>>>>> ones). Some of them did, though, already have their own context (for
>>>>> resource_copy_region, for instance) so I'm about to do this in a similar
>>>>> fashion.
>>>>> Actually, I was wondering if surface_destroy() should also get passed in
>>>>> a context - seems strange since it already stores the context, but this
>>>>> is exactly what sampler_view_destroy() does, which I'd like to see as a
>>>>> very analogous function.
>>>> Yes, it should take a context, mainly for consistency.  It helps when
>>>> wrapping/unwrapping these functions to have a consistent interface.  
>>> Yes.  The other reason is you have to be careful with objects that 
>>> save context pointers when those objects might be shared among 
>>> multiple contexts.
>>>
>>> If object A is created by context C1 and shared with context C2 and C1 
>>> gets destroyed, we're in trouble if we use A's stale context pointer. 
>>>   It's safer to use the context pointer that's passed to the function.
>>>
>>> I fixed a bug along those lines a couple months ago.  See 
>>> st_DeleteTextureObject().
>> Anything created by a context in gallium is private to that context.
>> The shareable entities are created in the screen.  In effect, Roland's
>> change makes surfaces private to the context.
>>
>> That may have effects elsewhere, eg in the mesa state tracker, which may
>> be relying on sharing surfaces (aka render_target_views,
>> depth_stencil_views) between contexts.
> 
> I am actually wondering if we should have some different abstraction for
> "surfaces" which are used for presents etc. Clearly, the glx etc. state
> trackers have no intention for using these pipe_resources as render
> attachment points, hence it's not really the right abstraction.
> But I guess that can be figured out later.

Actually, this turns out to be quite problematic. It really doesn't look
like the right abstraction at some places. Things like flush_frontbuffer
use pipe_surface, looks to me like they should just use the
pipe_resource instead (maybe hardcoded for level 0, layer 0 - I'm
sceptical anything else ever worked anyway)? Or is something else
entirely needed (that is a different "screen->get_dumb_2d_surface"
function)? It just seems like the hacks to use a context for getting a
pipe_surface which shouldn't really be needed in the first place are
just making things a mess.

Roland