[Mesa-dev] [PATCH] intel: Switch the order of the 2x MSAA sample positions

[Anuj Phogat]

On Wed, Aug 8, 2018 at 11:31 AM Jason Ekstrand <jason at jlekstrand.net> wrote:
>
> The Vulkan 1.1.82 spec flipped the order to better match D3D.
>
> Cc: mesa-stable at lists.freedesktop.org
> ---
>  src/intel/blorp/blorp_blit.c                       | 11 ++++++++++-
>  src/intel/common/gen_sample_positions.h            |  8 ++++----
>  src/mesa/drivers/dri/i965/brw_multisample_state.h  |  8 ++++----
>  src/mesa/drivers/dri/i965/gen6_multisample_state.c |  4 ++--
>  4 files changed, 20 insertions(+), 11 deletions(-)
>
> diff --git a/src/intel/blorp/blorp_blit.c b/src/intel/blorp/blorp_blit.c
> index 561897894c3..013f7a14fa2 100644
> --- a/src/intel/blorp/blorp_blit.c
> +++ b/src/intel/blorp/blorp_blit.c
> @@ -776,6 +776,13 @@ blorp_nir_manual_blend_bilinear(nir_builder *b, nir_ssa_def *pos,
>         * grid of samples with in a pixel. Sample number layout shows the
>         * rectangular grid of samples roughly corresponding to the real sample
>         * locations with in a pixel.
> +       *
> +       * In the case of 2x MSAA, the layout of sample indices is reversed from
> +       * the layout of sample numbers:
It is not clear from this comment if below layout is for sample index or sample
number. Adding "sample number layout:" on top of it will help.
> +       *           ---------
> +       *           | 1 | 0 |
> +       *           ---------
> +       *
>         * In case of 4x MSAA, layout of sample indices matches the layout of
>         * sample numbers:
>         *           ---------
> @@ -819,7 +826,9 @@ blorp_nir_manual_blend_bilinear(nir_builder *b, nir_ssa_def *pos,
>                                              key->x_scale * key->y_scale));
>        sample = nir_f2i32(b, sample);
>
> -      if (tex_samples == 8) {
> +      if (tex_samples == 2) {
> +         sample = nir_isub(b, nir_imm_int(b, 1), sample);
> +      } else if (tex_samples == 8) {
>           sample = nir_iand(b, nir_ishr(b, nir_imm_int(b, 0x64210573),
>                                         nir_ishl(b, sample, nir_imm_int(b, 2))),
>                             nir_imm_int(b, 0xf));
> diff --git a/src/intel/common/gen_sample_positions.h b/src/intel/common/gen_sample_positions.h
> index f0ce95dd1fb..da48dcb5ed0 100644
> --- a/src/intel/common/gen_sample_positions.h
> +++ b/src/intel/common/gen_sample_positions.h
> @@ -42,10 +42,10 @@ prefix##0YOffset   = 0.5;
>   * c   1
>   */
>  #define GEN_SAMPLE_POS_2X(prefix) \
> -prefix##0XOffset   = 0.25; \
> -prefix##0YOffset   = 0.25; \
> -prefix##1XOffset   = 0.75; \
> -prefix##1YOffset   = 0.75;
> +prefix##0XOffset   = 0.75; \
> +prefix##0YOffset   = 0.75; \
> +prefix##1XOffset   = 0.25; \
> +prefix##1YOffset   = 0.25;
>
>  /**
>   * Sample positions:
> diff --git a/src/mesa/drivers/dri/i965/brw_multisample_state.h b/src/mesa/drivers/dri/i965/brw_multisample_state.h
> index 6cf324e561c..2142a17a484 100644
> --- a/src/mesa/drivers/dri/i965/brw_multisample_state.h
> +++ b/src/mesa/drivers/dri/i965/brw_multisample_state.h
> @@ -38,13 +38,13 @@
>  /**
>   * 1x MSAA has a single sample at the center: (0.5, 0.5) -> (0x8, 0x8).
>   *
> - * 2x MSAA sample positions are (0.25, 0.25) and (0.75, 0.75):
> + * 2x MSAA sample positions are (0.75, 0.75) and (0.25, 0.25):
>   *   4 c
> - * 4 0
> - * c   1
> + * 4 1
> + * c   0
>   */
>  static const uint32_t
> -brw_multisample_positions_1x_2x = 0x0088cc44;
> +brw_multisample_positions_1x_2x = 0x008844cc;
>
>  /**
>   * Sample positions:
> diff --git a/src/mesa/drivers/dri/i965/gen6_multisample_state.c b/src/mesa/drivers/dri/i965/gen6_multisample_state.c
> index bfa84fb9b77..78ff3942075 100644
> --- a/src/mesa/drivers/dri/i965/gen6_multisample_state.c
> +++ b/src/mesa/drivers/dri/i965/gen6_multisample_state.c
> @@ -70,7 +70,7 @@ gen6_get_sample_position(struct gl_context *ctx,
>   *
>   * 2X MSAA sample index / number layout
You should update this comment matching it up with comment in blorp and
add  "sample number layout:" on top of below layout. I would leave it up to
you if you also want to draw sample index layout here just for uniformity.
>   *           ---------
> - *           | 0 | 1 |
> + *           | 1 | 0 |
>   *           ---------
>   *
>   * 4X MSAA sample index / number layout
> @@ -107,7 +107,7 @@ gen6_get_sample_position(struct gl_context *ctx,
>  void
>  gen6_set_sample_maps(struct gl_context *ctx)
>  {
> -   uint8_t map_2x[2] = {0, 1};
> +   uint8_t map_2x[2] = {1, 0};
>     uint8_t map_4x[4] = {0, 1, 2, 3};
>     uint8_t map_8x[8] = {3, 7, 5, 0, 1, 2, 4, 6};
>     uint8_t map_16x[16] = { 15, 10, 9, 7, 4, 1, 3, 13,
> --
> 2.17.1
>
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With above changes
Reviewed-by: Anuj Phogat <anuj.phogat at gmail.com>