[Mesa-dev] Gallium API questions

[Corbin Simpson]

On Wed, Jun 23, 2010 at 4:36 PM, Brian Paul <brianp at vmware.com> wrote:
> I'll try to answer a few...
>
>
> Corbin Simpson wrote:
>>
>> Yep, it's that time again. These are just things marked in the docs as
>> unknown, so I'm not grinding any axes, just cleaning stuff up.
>>
>> ~ "If a surface includes several layers/slices (XXX: not yet...) then
>> all layers will be cleared." From the information on
>> pipe_context::clear(). Is this just wishful thinking, or do drivers
>> need to implement this?
>>
>> ~ An explanation of dual-source blends and how they work would be nice.
>
> Marek provided a pointer, but I don't think we've done anything with this in
> gallium yet.
>
>> ~ If logicop_enable and independent_blend_enable are set, are lops
>> performed for all render targets, or only those that have blend_enable
>> set?
>
> The GL_ARB_drawbuffers2 spec is a bit vague on this but in swrast logicop
> had precedence over blending and either applies to all color buffers or
> none.
>
>> ~ PIPE_CAP_GUARD_BAND_* obviously refers to the guard bands, but what
>> exactly do they mean as capabilities? Maximum guard band settings?
>> Minimum?
>
> They're probably the guard band width in pixels.
>
>> ~ Are we going to introduce new cap bits for parts of the TGSI ISA?
>> (I'll understand if this is off the table for now.)
>>
>> ~ What are the components of textures in the UV or Z format when
>> sampled? For UV, current candidates are (0, 0, 0, 1) and (u, v, 1, 1).
>> The latter seems more reasonable given that Gallium is shaderful. For
>> Z, it could be (z, z, z, 1), (0, z, 0, 1), (0, 0, 0, z), or (z, z, z,
>> z) and is configurable in GL. Maybe we want to have this be
>> configurable?

Very cool. I like the new information, although a couple pieces of
information vanished.

We currently allow partial specification of position, requiring only
(x, y) and filling in z as 0 and w as 1 if missing. Is that still
valid? Similarly, colors may be specified as (r, g, b) triplets with
no alpha, and alpha defaults to 1. Is that still valid, or are there
changes further up the API that make this not needed?

~ C.

-- 
When the facts change, I change my mind. What do you do, sir? ~ Keynes

Corbin Simpson
<MostAwesomeDude at gmail.com>