[Mesa-dev] [PATCH 2/5] radeonsi: use guard band clipping

[Nicolai Hähnle]

On 12.04.2016 07:45, Marek Olšák wrote:
> On Tue, Apr 12, 2016 at 1:53 AM, Marek Olšák <maraeo at gmail.com> wrote:
>> On Mon, Apr 11, 2016 at 7:37 PM, Nicolai Hähnle <nhaehnle at gmail.com> wrote:
>>> On 10.04.2016 17:34, Marek Olšák wrote:
>>>>
>>>> From: Marek Olšák <marek.olsak at amd.com>
>>>>
>>>> Guard band clipping speeds up rasterization for primitives that are
>>>> partially off-screen.  This change in particular results in small
>>>> framerate improvements in a wide range of games.
>>>>
>>>> Started by Grigori Goronzy <greg at chown.ath.cx>.
>>>> ---
>>>>    src/gallium/drivers/radeonsi/si_state.c | 73
>>>> +++++++++++++++++++++++++++++++--
>>>>    1 file changed, 69 insertions(+), 4 deletions(-)
>>>>
>>>> diff --git a/src/gallium/drivers/radeonsi/si_state.c
>>>> b/src/gallium/drivers/radeonsi/si_state.c
>>>> index b5db456..bc04b46 100644
>>>> --- a/src/gallium/drivers/radeonsi/si_state.c
>>>> +++ b/src/gallium/drivers/radeonsi/si_state.c
>>>> @@ -887,6 +887,15 @@ static void si_clip_scissor(struct pipe_scissor_state
>>>> *out,
>>>>          out->maxy = MIN2(out->maxy, clip->maxy);
>>>>    }
>>>>
>>>> +static void si_scissor_make_union(struct si_signed_scissor *out,
>>>> +                                 struct si_signed_scissor *in)
>>>> +{
>>>> +       out->minx = MIN2(out->minx, in->minx);
>>>> +       out->miny = MIN2(out->miny, in->miny);
>>>> +       out->maxx = MAX2(out->maxx, in->maxx);
>>>> +       out->maxy = MAX2(out->maxy, in->maxy);
>>>> +}
>>>> +
>>>>    static void si_emit_one_scissor(struct radeon_winsys_cs *cs,
>>>>                                  struct si_signed_scissor *vp_scissor,
>>>>                                  struct pipe_scissor_state *scissor)
>>>> @@ -908,12 +917,64 @@ static void si_emit_one_scissor(struct
>>>> radeon_winsys_cs *cs,
>>>>                          S_028254_BR_Y(final.maxy));
>>>>    }
>>>>
>>>> +/* the range is [-MAX, MAX] */
>>>> +#define SI_MAX_VIEWPORT_RANGE 32768
>>>> +
>>>> +static void si_emit_guardband(struct si_context *sctx,
>>>> +                             struct si_signed_scissor *vp_as_scissor)
>>>> +{
>>>> +       struct radeon_winsys_cs *cs = sctx->b.gfx.cs;
>>>> +       struct pipe_viewport_state vp;
>>>> +       float left, top, right, bottom, max_range, guardband_x,
>>>> guardband_y;
>>>> +
>>>> +       /* Reconstruct the viewport transformation from the scissor. */
>>>> +       vp.translate[0] = (vp_as_scissor->minx + vp_as_scissor->maxx) /
>>>> 2.0;
>>>> +       vp.translate[1] = (vp_as_scissor->miny + vp_as_scissor->maxy) /
>>>> 2.0;
>>>> +       vp.scale[0] = vp_as_scissor->maxx - vp.translate[0];
>>>> +       vp.scale[1] = vp_as_scissor->maxy - vp.translate[1];
>>>> +
>>>> +       /* Treat a 0x0 viewport as 1x1 to prevent division by zero. */
>>>> +       if (vp_as_scissor->minx == vp_as_scissor->maxx)
>>>> +               vp.scale[0] = 0.5;
>>>> +       if (vp_as_scissor->miny == vp_as_scissor->maxy)
>>>> +               vp.scale[1] = 0.5;
>>>> +
>>>> +       /* Find the biggest guard band that is inside the supported
>>>> viewport
>>>> +        * range. The guard band is specified as a horizontal and vertical
>>>> +        * distance from (0,0) in clip space.
>>>> +        *
>>>> +        * This is done by applying the inverse viewport transformation
>>>> +        * on the viewport limits to get those limits in clip space.
>>>> +        *
>>>> +        * Use a limit one pixel smaller to allow for some precision
>>>> error.
>>>> +        */
>>>> +       max_range = SI_MAX_VIEWPORT_RANGE - 1;
>>>> +       left   = (-max_range - vp.translate[0]) / vp.scale[0];
>>>> +       right  = ( max_range - vp.translate[0]) / vp.scale[0];
>>>> +       top    = (-max_range - vp.translate[1]) / vp.scale[1];
>>>> +       bottom = ( max_range - vp.translate[1]) / vp.scale[1];
>>>> +
>>>> +       assert(left < 0 && top < 0 && right > 0 && bottom > 0);
>>>
>>>
>>> The viewport transform is supplied directly by the user, isn't it? So if
>>> they provide a crazy transform, this assert might trigger. On the other
>>> hand, for reasonable viewport transforms, it should even be the case that
>>> left <= -1.0, right >= 1.0, and so on, right? I guess what I'm saying is
>>> that the spirit of the assert is good and could probably be even
>>> strengthened, but in reality it probably needs to go away.
>>>
>>> In a similar spirit, perhaps guardband_x/y should be bounded to be at least
>>> 1.0?
>>
>> glViewport is clamped to ctx->Const.ViewportBounds.Min/Max. This
>> assures that all guard bands are >= 1. However, if we get invalid
>> coordinates from other sources, the guard band must prevent generating
>
> That should be "if we get invalid viewport transform from other sources".
>
> I think the assertion should stay and be strengthened to "x >= 1", because:
> - we don't know how the discard guard band interacts with the clip guard band
> - we should keep the assertion to prevent and detect possible
> corruption caused by invalid viewport transformation
>
> Does this sound good?

Yes, sounds good. With these changes, you can add my R-b to this patch 
as well.

Cheers,
Nicolai

>
> Marek
>