[Mesa-dev] [PATCH] radv: Rework guard band calculation.

[Dave Airlie]

On 2 April 2017 at 22:43, Bas Nieuwenhuizen <bas at basnieuwenhuizen.nl> wrote:
> We want the guardband_x/y to be the largerst scalars such that each
> viewport scaled by that amount is still a subrange of [-32767, 32767].
>
> The old code has a couple of issues:
> 1) It used scissor instead of viewport_scissor, potentially taking into
>    account a viewport that is too small and therefore selecting a scale
>    that is too large.
> 2) Merging the viewports isn't ideal, as for example viewports with
>    boundaries [0,1] and [1000, 1001] would allow a guardband scale of ~30k,
>    while their union [0, 1001] only allows a scale of ~32.
>
> The new code just determines the guardband per viewport and takes the minimum.
>
> Signed-off-by: Bas Nieuwenhuizen <basni at google.com>

I'm not sure I understand guardband enough to say I know what this is doing,

Acked-by: Dave Airlie <airlied at redhat.com>

> ---
>  src/amd/vulkan/si_cmd_buffer.c | 52 ++++++++++--------------------------------
>  1 file changed, 12 insertions(+), 40 deletions(-)
>
> diff --git a/src/amd/vulkan/si_cmd_buffer.c b/src/amd/vulkan/si_cmd_buffer.c
> index e176abe3869..bbcaf1009bd 100644
> --- a/src/amd/vulkan/si_cmd_buffer.c
> +++ b/src/amd/vulkan/si_cmd_buffer.c
> @@ -504,22 +504,6 @@ get_viewport_xform(const VkViewport *viewport,
>         translate[2] = n;
>  }
>
> -static void
> -get_viewport_xform_scissor(const VkRect2D *scissor,
> -                           float scale[2], float translate[2])
> -{
> -       float x = scissor->offset.x;
> -       float y = scissor->offset.y;
> -       float half_width = 0.5f * scissor->extent.width;
> -       float half_height = 0.5f * scissor->extent.height;
> -
> -       scale[0] = half_width;
> -       translate[0] = half_width + x;
> -       scale[1] = half_height;
> -       translate[1] = half_height + y;
> -
> -}
> -
>  void
>  si_write_viewport(struct radeon_winsys_cs *cs, int first_vp,
>                    int count, const VkViewport *viewports)
> @@ -579,26 +563,13 @@ static VkRect2D si_intersect_scissor(const VkRect2D *a, const VkRect2D *b) {
>         return ret;
>  }
>
> -static VkRect2D si_union_scissor(const VkRect2D *a, const VkRect2D *b) {
> -       VkRect2D ret;
> -       ret.offset.x = MIN2(a->offset.x, b->offset.x);
> -       ret.offset.y = MIN2(a->offset.y, b->offset.y);
> -       ret.extent.width = MAX2(a->offset.x + a->extent.width,
> -                               b->offset.x + b->extent.width) - ret.offset.x;
> -       ret.extent.height = MAX2(a->offset.y + a->extent.height,
> -                                b->offset.y + b->extent.height) - ret.offset.y;
> -       return ret;
> -}
> -
> -
>  void
>  si_write_scissors(struct radeon_winsys_cs *cs, int first,
>                    int count, const VkRect2D *scissors,
>                    const VkViewport *viewports, bool can_use_guardband)
>  {
>         int i;
> -       VkRect2D merged;
> -       float scale[2], translate[2], guardband_x = 1.0, guardband_y = 1.0;
> +       float scale[3], translate[3], guardband_x = INFINITY, guardband_y = INFINITY;
>         const float max_range = 32767.0f;
>         assert(count);
>
> @@ -607,10 +578,14 @@ si_write_scissors(struct radeon_winsys_cs *cs, int first,
>                 VkRect2D viewport_scissor = si_scissor_from_viewport(viewports + i);
>                 VkRect2D scissor = si_intersect_scissor(&scissors[i], &viewport_scissor);
>
> -               if (i)
> -                       merged = si_union_scissor(&merged, &scissor);
> -               else
> -                       merged = scissor;
> +               get_viewport_xform(viewports + i, scale, translate);
> +               if (scale[0] < 0.5)
> +                       scale[0] = 0.5;
> +               if (scale[1] < 0.5)
> +                       scale[1] = 0.5;
> +
> +               guardband_x = MIN2(guardband_x, (max_range - abs(translate[0])) / scale[0]);
> +               guardband_y = MIN2(guardband_y, (max_range - abs(translate[1])) / scale[1]);
>
>                 radeon_emit(cs, S_028250_TL_X(scissor.offset.x) |
>                             S_028250_TL_Y(scissor.offset.y) |
> @@ -618,12 +593,9 @@ si_write_scissors(struct radeon_winsys_cs *cs, int first,
>                 radeon_emit(cs, S_028254_BR_X(scissor.offset.x + scissor.extent.width) |
>                             S_028254_BR_Y(scissor.offset.y + scissor.extent.height));
>         }
> -
> -       get_viewport_xform_scissor(&merged, scale, translate);
> -
> -       if (can_use_guardband) {
> -               guardband_x = (max_range - abs(translate[0])) / scale[0];
> -               guardband_y = (max_range - abs(translate[1])) / scale[1];
> +       if (!can_use_guardband) {
> +               guardband_x = 1.0;
> +               guardband_y = 1.0;
>         }
>
>         radeon_set_context_reg_seq(cs, R_028BE8_PA_CL_GB_VERT_CLIP_ADJ, 4);
> --
> 2.12.1
>
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