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

[Matteo Bruni]

On Fri, Sep 10, 2021 at 1:32 AM Zebediah Figura (she/her)
<zfigura at codeweavers.com> wrote:
>
> On 9/9/21 6:16 PM, Matteo Bruni wrote:
> > On Thu, Sep 9, 2021 at 6:02 AM Zebediah Figura <zfigura at codeweavers.com> wrote:
> >>
> >> Signed-off-by: Zebediah Figura <zfigura at codeweavers.com>
> >> ---
> >>   libs/vkd3d-shader/hlsl_sm4.c | 34 ++++++++++++++++++++++++++++++++++
> >>   1 file changed, 34 insertions(+)
> >>
> >> diff --git a/libs/vkd3d-shader/hlsl_sm4.c b/libs/vkd3d-shader/hlsl_sm4.c
> >> index 160da47fd..cac71ef7e 100644
> >> --- a/libs/vkd3d-shader/hlsl_sm4.c
> >> +++ b/libs/vkd3d-shader/hlsl_sm4.c
> >> @@ -981,6 +981,40 @@ static void write_sm4_expr(struct hlsl_ctx *ctx,
> >>           {
> >>               switch (expr->op)
> >>               {
> >> +                case HLSL_OP1_CAST:
> >> +                {
> >> +                    const struct hlsl_type *src_type = arg1->data_type;
> >> +
> >> +                    /* Narrowing casts need to be lowered. */
> >> +                    if (src_type->dimx != expr->node.data_type->dimx)
> >> +                        hlsl_fixme(ctx, expr->node.loc, "Narrowing cast.\n");
> >> +
> >> +                    switch (src_type->base_type)
> >> +                    {
> >> +                        case HLSL_TYPE_HALF:
> >> +                        case HLSL_TYPE_FLOAT:
> >> +                            write_sm4_unary_op(buffer, VKD3D_SM4_OP_MOV, &expr->node, arg1, 0);
> >> +                            break;
> >> +
> >> +                        case HLSL_TYPE_BOOL:
> >> +                        case HLSL_TYPE_INT:
> >> +                            write_sm4_unary_op(buffer, VKD3D_SM4_OP_ITOF, &expr->node, arg1, 0);
> >> +                            break;
> >
> > 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.
> >
> > That's probably the reason why native uses MOVC to convert from bool
> > (to float or anything else) and, most importantly, NE for the opposite
> > direction (with 0 as the other comparand).
> >
>
> "(int)(bool)true" evaluates to 1 in anything I've been able to test.
> Under what circumstances do you have it evaluating to ~0?

Yeah, the bool -> int conversion explicitly makes sure to give you 1
(by means of the MOVC instruction). You need to look at the generated
shader bytecode.
Try with this shader:

bool4 main(uniform int i, uniform uint u, uniform bool b, uniform
float f) : sv_target
{
    return bool4(((float)(bool)i) + 1.5, ((float)(bool)u) - 2.5,
((float)(bool)b) / 2, f);
}