tu: allow D3D-compatible texture coordinate rounding

When running under DXVK or vkd3d, the texture coordinate rounding behavior
should match D3D expectations. On Adreno, this behavior can be toggled
through the SP_TP_MODE_CNTL register.

A driconf-based option is introduced to help set the relevant register flag
that enables this behavior.

This fixes the cause of test_sampler_rounding test case failure in vkd3d on
Turnip's side, but a small change in vkd3d is also required, so the test
failure expectation isn't removed yet.

Signed-off-by: Zan Dobersek <zdobersek@igalia.com>
Reviewed-by: Rob Clark <robdclark@chromium.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/33987>

src/freedreno/vulkan/tu_cmd_buffer.cc

@@ -1528,7 +1528,9 @@ tu6_init_static_regs(struct tu_device *dev, struct tu_cs *cs)
    tu_cs_emit_write_reg(cs, REG_A6XX_VPC_UNKNOWN_9602, 0);
    tu_cs_emit_write_reg(cs, REG_A6XX_PC_UNKNOWN_9E72, 0);
    tu_cs_emit_regs(cs, A6XX_SP_TP_MODE_CNTL(.isammode = ISAMMODE_GL,
-                                            .texcoordroundmode = COORD_TRUNCATE,
+                                            .texcoordroundmode = dev->instance->use_tex_coord_round_nearest_even_mode
+                                               ? COORD_ROUND_NEAREST_EVEN
+                                               : COORD_TRUNCATE,
                                             .nearestmipsnap = CLAMP_ROUND_TRUNCATE,
                                             .destdatatypeoverride = true));
    tu_cs_emit_regs(cs, HLSQ_CONTROL_5_REG(CHIP, .dword = 0xfc));

src/freedreno/vulkan/tu_device.cc

@@ -1635,6 +1635,7 @@ static const driOptionDescription tu_dri_options[] = {
       DRI_CONF_TU_DONT_RESERVE_DESCRIPTOR_SET(false)
       DRI_CONF_TU_ALLOW_OOB_INDIRECT_UBO_LOADS(false)
       DRI_CONF_TU_DISABLE_D24S8_BORDER_COLOR_WORKAROUND(false)
+      DRI_CONF_TU_USE_TEX_COORD_ROUND_NEAREST_EVEN_MODE(false)
    DRI_CONF_SECTION_END
 };
 
@@ -1657,6 +1658,8 @@ tu_init_dri_options(struct tu_instance *instance)
          driQueryOptionb(&instance->dri_options, "tu_allow_oob_indirect_ubo_loads");
    instance->disable_d24s8_border_color_workaround =
          driQueryOptionb(&instance->dri_options, "tu_disable_d24s8_border_color_workaround");
+   instance->use_tex_coord_round_nearest_even_mode =
+         driQueryOptionb(&instance->dri_options, "tu_use_tex_coord_round_nearest_even_mode");
 }
 
 static uint32_t instance_count = 0;

src/freedreno/vulkan/tu_device.h

@@ -204,6 +204,9 @@ struct tu_instance
     * UBWC to be enabled.
     */
    bool disable_d24s8_border_color_workaround;
+
+   /* D3D emulation requires texture coordinates to be rounded to nearest even value. */
+   bool use_tex_coord_round_nearest_even_mode;
 };
 VK_DEFINE_HANDLE_CASTS(tu_instance, vk.base, VkInstance,
                        VK_OBJECT_TYPE_INSTANCE)

src/util/00-mesa-defaults.conf

@@ -1245,6 +1245,12 @@ TODO: document the other workarounds.
                 to ignore this edge case and force UBWC to be enabled.
             -->
             <option name="tu_disable_d24s8_border_color_workaround" value="true" />
+            <!--
+                For sampling, Vulkan requires texture coordinates to be truncated, whereas
+                D3D requires them to be rounded to nearest even value. The former is used by
+                default, the latter is used through this option.
+            -->
+            <option name="tu_use_tex_coord_round_nearest_even_mode" value="true" />
         </engine>
     </device>
 

src/util/driconf.h

@@ -641,6 +641,10 @@
    DRI_CONF_OPT_B(tu_disable_d24s8_border_color_workaround, def, \
                   "Use UBWC for D24S8 images with VK_IMAGE_USAGE_SAMPLED_BIT when customBorderColorWithoutFormat is enabled")
 
+#define DRI_CONF_TU_USE_TEX_COORD_ROUND_NEAREST_EVEN_MODE(def) \
+   DRI_CONF_OPT_B(tu_use_tex_coord_round_nearest_even_mode, def, \
+                  "Use D3D-compliant round-to-nearest-even mode for texture coordinates")
+
 /**
  * \brief Honeykrisp specific configuration options
  */