[Mesa-dev] [PATCH 0/5] Gallium: Passing drirc options to create_screen() and fixing Rocket League

[Rob Clark]

On Wed, Jun 21, 2017 at 8:15 PM, Marek Olšák <maraeo at gmail.com> wrote:
> On Wed, Jun 21, 2017 at 10:37 PM, Rob Clark <robdclark at gmail.com> wrote:
>> On Tue, Jun 20, 2017 at 6:54 PM, Marek Olšák <maraeo at gmail.com> wrote:
>>> Hi,
>>>
>>> This series updates pipe loaders so that flags such as drirc options
>>> can be passed to create_screen(). I have compile-tested everything
>>> except clover.
>>>
>>> The first pipe_screen flag is a drirc option to fix incorrect grass
>>> rendering in Rocket League for radeonsi. Rocket League expects DirectX
>>> behavior for partial derivative computations after discard/kill, but
>>> radeonsi implements the more efficient but stricter OpenGL behavior
>>> and that will remain our default behavior. The new screen flag forces
>>> radeonsi to use the DX behavior for that game.
>>>
>>
>> do we really want this to be a *global* option for the screen?
>
> Yes. Shaders are pipe_screen (global) objects in radeonsi, so a
> compiler option also has to be global. We can't look at the context
> during the TGSI->LLVM translation.

well, I didn't really mean per-screen vs per-context, as much as
per-screen vs per-shader (or maybe more per-screen vs
per-instruction?)

>>
>> I'm just thinking, some drivers use lowering passes that internally
>> generate kill's.  I *guess* it would only matter if they also had
>> ddx/ddy instructions, but not sure.
>>
>> not really sure if this would actually be a problem or not..
>
> Whether or not this affects you depends on how your hardware
> implements kill/discard. Not just ddx/ddy, texture instructions
> computing derivatives internally are affected by kill/discard too.
>

I guess most of the lowering passes that introduce kill's are more
like legacy gl things (clip-planes, glBitmap(), maybe some others but
pretty sure it is all legacy type stuff), so maybe it isn't likely to
matter.  I'm not totally sure about the expected interactions between
kill and other instructions, so not totally sure about whether I
should care.. but figured I should point it out.. and if it doesn't
matter, it doesn't matter.

BR,
-R