[Mesa-dev] Gallium API questions

[Corbin Simpson]

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.

~ If logicop_enable and independent_blend_enable are set, are lops
performed for all render targets, or only those that have blend_enable
set?

~ PIPE_CAP_TEXTURE_SHADOW_MAP and PIPE_CAP_MAX_PREDICATE_REGISTERS
aren't explained.

~ PIPE_CAP_GUARD_BAND_* obviously refers to the guard bands, but what
exactly do they mean as capabilities? Maximum guard band settings?
Minimum?

~ Could somebody explain exactly what's up with the RCC opcode? Its
definition is kind of ridiculous: dst = (1 / src.x) > 0 ? clamp(1 /
src.x, 5.42101e-020, 1.884467e+019) : clamp(1 / src.x, -1.884467e+019,
-5.42101e-020)

~ 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.)

~ TGSI_SEMANTIC_POSITION is (x, y, z, w) where x, y, and z are
position, and w is the homogeneous coordinate. Is w also for
perspective divide? Is the perspective divide configurable, or is it
always done in shaders?

~ "Position, if not specified, usually defaults to (0, 0, 0, 1), and
can be partially specified as (x,  y, 0, 1) or (x, y, z,  1)."
"Usually" is probably Corbin-speak for "I'm just guessing here." Is
that actually how it goes, or is position mandatory?

~ Can somebody explain the format of TGSI_SEMANTIC_EDGEFLAG?

~ 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?

Thanks!

~ C.

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

Corbin Simpson
<MostAwesomeDude at gmail.com>