On 07/05/18 20:36, Jason Ekstrand wrote: > On Mon, May 7, 2018 at 9:37 AM, Kenneth Graunke <kenn...@whitecape.org > <mailto:kenn...@whitecape.org>> wrote: > > On Monday, May 7, 2018 8:53:34 AM PDT Jason Ekstrand wrote: > > On Mon, May 7, 2018 at 8:02 AM, Alejandro Piñeiro > <apinhe...@igalia.com <mailto:apinhe...@igalia.com>> > > wrote: > > > > > Hi Jason, > > > > > > as part of the ARB_gl_spirv work, we are doing the linking > based on the > > > nir shader that comes from spirv_to_nir. On some cases, > > > nir_lower_wpos_ytransform introduces a new uniform, > > > "gl_FbWposYTransform". So as the uniform is there when we > start to do > > > the linking, it is treated as any other uniform, being added > to the > > > UniformStorage, accessible through the OpenGL API and so on. > Something > > > that I understand that we don't want. On GLSL this is not a > problem > > > because the linking is done based on MESA/IR, then the IR is > converted > > > to NIR, and the lowering adds the uniform based on the NIR shader, > > > really after the linking. > > > > > > The first solution I thought was just mark the uniform with a > special > > > location [1]. It would need to be a negative value, not -1 that is > > > already reserved for not-assigned locations (we still have > some cases > > > for those, even if in general ARB_gl_spirv makes explicit location > > > mandatory). So it would be a new negative value, like lets say > -5. So > > > then on the linking, if the uniform location has this value, > the uniform > > > is skipped. > > > > > > After checking that this solution worked (although I only > tested with > > > some tests), I started to search for an alternative, as this > solution > > > seemed too hacky. > > > > > > It does seem a bit hacky, yes. > > > > > > > But this lowering needs to be run before nir_lower_io, > > > and nir_lower_io is part of the uniform lowering. So I didn't > see really > > > reasonable to do a nir_lower_io without > nir_lower_wpos_ytransform, do > > > the linking, and then execute again > nir_lower_io/nir_lower_wpos_transform. > > > > > > > This is all a bit sticky. One observation is that the newly > added uniform > > makes usage of the token system. Are tokens no longer used with > SPIR-V? I > > guess they are kind-of an old mechanism to handle the crufty ARB > program > > parameters. However, you could have -5 mean "It uses a token" > > > > Another option would be to use a system value instead of a > uniform. We can > > then convert it to a uniform in the back-end. We have a few > places where > > we do things like this for compute shaders. > > > > I don't have a lot of good ideas or strong opinions, I'm afraid. > :-( Maybe > > Ken has some? > > > > --Jason > > In GLSL IR, we use var->how_declared == ir_var_hidden to hide > internally > created variables from API introspection. Why not just port something > similar over to the newer NIR code? > > > I wasn't aware of that. If we're going to do linking in NIR, > something like that is probably needed.
Oh nice. Yes, I wasn't aware neither. I will add try to add a similar mechanism on NIR. Thanks everybody for the feedback. BR
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