[Mesa-dev] [PATCH] st/mesa: optionally apply texture swizzle to border color
Roland Scheidegger
sroland at vmware.com
Sun Apr 14 09:20:59 PDT 2013
Oh and btw how does this work for real hw, if the hardware indeed
interpets the border color value according to format?
Are there some bits to set that the border color value is either
interpreted according to format (useful for opengl) or always as float
(useful for d3d10)? Or how else do you use the same sampler for
different int/float textures?
This discrepancy between OpenGL and d3d10 is quite a mess.
Roland
Am 14.04.2013 17:45, schrieb Roland Scheidegger:
> Yeah it is ok for OpenGL. I guess for d3d10 we'd probably need to create
> another sampler if the same sampler is used for both int and float
> textures. Or just supply both int and float border colors to the sample
> code (but making it work both for opengl and d3d would be ugly). FWIW it
> looks like some intel hw also seems to require multiple border color
> values (and 6!!! ones at that), and the hw just picks the right value
> based on format. Though for some reason the only border color format it
> does _not_ have is 32bit int, so it looks this does absolutely nothing
> to make both float and 32bit int colors work with the same sampler
> simultaneously (and I guess 32bit int is probably the reason opengl
> specifies those as ints, since you can't get accurate values with floats).
> The swizzling looks like an orthogonal issue to that, however.
>
> Roland
>
>
> Am 14.04.2013 16:18, schrieb Marek Olšák:
>> The border color in the sampler state is untyped and that's okay. The
>> type is irrelevant with nearest filtering - just memcpy the border color
>> to the destination register (if there is swizzling, just do what you do
>> for texels). With linear filtering, you can always assume it's float
>> (regardless of the sampler view).
>>
>> Marek
>>
>>
>> On Sun, Apr 14, 2013 at 3:34 PM, Jose Fonseca <jfonseca at vmware.com
>> <mailto:jfonseca at vmware.com>> wrote:
>>
>>
>>
>> ----- Original Message -----
>> > On 14.04.2013 13:44, Jose Fonseca wrote:
>> > > ----- Original Message -----
>> > >> From: Christoph Bumiller <christoph.bumiller at speed.at
>> <mailto:christoph.bumiller at speed.at>>
>> > >>
>> > >> This is the only sane solution for nv50 and nvc0 (really, trust
>> me),
>> > >> but since on other hardware the border colour is tightly
>> coupled with
>> > >> texture state they'd have to undo the swizzle, so I've added a cap.
>> > >>
>> > >> The name of the cap could be changed to be more descriptive, like
>> > >> PIPE_CAP_TEXTURE_SWIZZLE_AFFECTS_BORDER_COLOR.
>> > > Yes, please.
>> > >
>> > >> The dependency of update_sampler on the texture updates was
>> > >> introduced to avoid doing the apply_depthmode to the swizzle twice.
>> > >>
>> > >> More detailed explanation of driver situation:
>> > >>
>> > >> No, really, don't suggest doing this in the driver. The driver has
>> > >> elegantly separated texture view and sampler states (which are each
>> > >> a structure in a table in VRAM and should not be updated to avoid
>> > >> performance loss), and table are bound to the independent (!)
>> > > I wonder if this is modeled after D3D10, where sampler state is
>> independent
>> > > from resource view state. Though as far as I known, D3D10's
>> interpretation
>> > > of texture border color does not depend on the swizzle...
>> > >
>> > >> texture
>> > >> and sampler slots in shaders which must be separately indexable
>> > >> indirectly).
>> > >> So, if I was to do this in the driver, I'd have to add separate
>> sampler
>> > >> state object instances for each texture view with appropriately
>> swizzled
>> > >> border color, and there's only 16 slots, so I'd be limited to 4
>> texture
>> > >> units.
>> > >> Not to mention the sheer insanity, ugliness and emotional pain
>> incurred
>> > >> when writing that code when it COULD be so easy and simple in
>> the state
>> > >> tracker where you know that textures and samplers are tightly
>> coupled,
>> > >> while in gallium I cannot assume that to be the case.
>> > > You wouldn't really need to create all state combinations: if
>> you known
>> > > that textures and samplers are tightly coupled, then caching the
>> actually
>> > > used combinations will get you exactly the same behavior,
>> without losing
>> > > performance or generality. But granted, this would require more
>> effort.
>> >
>> > The emphasize being on "IF I knew" (that they're tighly coupled). If I
>> > did, I could switch to linked mode where the card automatically
>> uses the
>> > view index as sampler index, ignoring the actual sampler index, and
>> > validate them together.
>> > However, that only applies to 3D, not to COMPUTE (which means that GL
>> > compute shaders will still have the problem), and I'd have to support
>> > both variants for state trackers that do not allow the coupling,
>> and we
>> > need a way for the state tracker to actually tell us what it
>> wants. All
>> > that makes it even quirkier.
>> >
>> > > Also please spare a thought for other state trackers -- and I'm
>> not even
>> > > talking about a potential D3D10 state tracker for which your
>> driver would
>> > > be unusable --, even inside Mesa: it seems like
>> > > src/gallium/state_trackers/vega uses both texture border and
>> swizzle,
>> > > probably vl state tracker too, so your driver will be busted on
>> those
>> > > state trackers. These need to be
>> >
>> > It already is busted. It's also busted on r600 where making border
>> color
>> > + swizzle work properly isn't even POSSIBLE (according to the
>> radeon guys).
>> >
>> > Maybe not for vega, it doesn't use a permutational swizzle, it
>> just sets
>> > components to PIPE_SWIZZLE_ONE, and incidentally the ZERO/ONE swizzles
>> > do affect the border color. As far as I can tell, it looks something
>> > like this (if you're interested; the exact behaviour seems not
>> supposed
>> > to be made use of):
>> >
>> > ===
>> > In the format description (including swizzle), each color component of
>> > RGBA (as seen by the shader) gets mapped a memory component
>> > {C0,C1,C2,C3} or {ZERO,ONE_INT,ONE_FLOAT}.
>> >
>> > When a memory (!) component (Cx) is first encountered when going
>> through
>> > RGBA, it is assigned the SAMPLER_BORDER_COLOR component value for that
>> > component, and if the memory component is encountered again
>> (because of
>> > swizzle), that same value will be used.
>> >
>> > So, assuming memory format RGBA and the swizzle 1RBG:
>> > R = ONE
>> > G = C0
>> > B = C2
>> > A = C1
>> > the border colour will be SAMPLER_BORDER_COLOR.1GBA.
>> >
>> > The resulting border colour with swizzle applied to the sampler
>> would be
>> > (lowercase being user values):
>> > R=1
>> > G=r
>> > B=b
>> > A=g
>> >
>> > resulting in 1rbg, which works out.
>> > ===
>> >
>> > > updated -- maybe the burden of considering this state can be
>> lifted onto
>> > > some helper functinons -- if not, these state trackers should
>> at least be
>> > > updated to abort/warn when the cap is set.
>> > >
>> > > But I'm not really objecting -- as texture border seems
>> fundamentally
>> > > quirky state. But before proceeding with this I'd like us to
>> consider
>> > > another texture border quirk while we are at it.
>> > >
>> > > The other quirk is the integer vs float texture border colors.
>> Roland can
>> > > probably talk a bit more about it as he was the one who came
>> across it.
>> > > In a few words, the interpretation of texture border color union
>> depends
>> > > on the format in the sampler view state (whether it's a pure integer
>> > > format or not).
>> > >
>> > > So, I wonder how integer vs float texture border colors will fit
>> in your
>> > > driver's "elegantly separated texture view and sampler states",
>> or any
>> > > other driver for that matter. That is, will the world need a
>> > > PIPE_CAP_SAMPLER_VIEW_FORMAT_VIEW_AFFECTS_TEXTURE_BORDER_COLOR
>> too? If so
>> > > then maybe we want to lump these two things together.
>> >
>> > No, you can relax there, because using a sampler with integer border
>> > colors with a float texture view (which doesn't happen in OpenGL) or
>> > vice versa is not SUPPOSED to work (or even, supposed to not work),
>> > while texture swizzle IS, it has no such incompatibility.
>>
>> Fair enough. But note that Gallium pipe_sampler_state's border_color
>> member doesn't describe whether it is float or integer.
>>
>> Furthermore, given that cso module is not able to distinguish a
>> sampler state with (1.0f, 1.0f, 1.0f, 1.0f) border color, from one
>> with (0x3f800000U, 0x3f800000U, 0x3f800000U, 0x3f800000U), it would
>> happily create the same driver handle for both.
>>
>> That is, even if this situation doesn't happen with OpenGL, it's
>> still not clear how will drivers handle it.
>>
>> Also D3D10 does allow using sample sampler state with both
>> integer/float texture views, although D3D10's texture borders are
>> always float regardless (even for integer formats), so it has no
>> ambiguities either.
>>
>> Jose
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