[PATCH vkd3d 5/7] vkd3d-shader/hlsl: Write SM4 casts to float.

[Giovanni Mascellani]

Hi,

Il 10/09/21 01:16, Matteo Bruni ha scritto:
> As far as I'm aware, booleans in SM4+ are represented in quite a
> peculiar way: false is represented as 0, true is canonically
> 0xffffffff. I think the idea is to be able to use the result of a
> conditional expression directly as a mask and such, but don't quote me
> on that. For sure it's different from SM1-3, which use the traditional
> 0 and 1 values for false and true.

Well, isn't it our choice how we decide to represent things internally? 
The only important requirement is that casts (and everything else) have 
the correct semantics. Whether inside a true bool variable there is 1, 
~0u or whatever else it's our decision. If we store 1 for true, then we 
have to use MOVC (or a comparison followed by INEG) when casting to bool 
and MOV or ITOF when casting to int or float. If we store ~0, then we 
use a simple comparison for casting to bool and MOVC (or INEG and 
possibly ITOF) to cast to int or float.

In case we want to be closer to native (though I'm not sure it's really 
a requirement in this case: I expect all this opcodes to be well 
supported everywhere), then probably choosing to represent true as ~0u 
is better, but it's just a matter of choice. The really important thing 
is to be aware and consistent with the choice.

So what do we decide? I already have patches that implements comparison 
operators that assume that true is represented as 1. I can fix them, but 
please tell me what do we want.

Giovanni.