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

[Jason Ekstrand]

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:
+       *           ---------
+       *           | 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
  *           ---------
- *           | 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