From 6b211e9b43576150611d482b2d3865318f8b61f7 Mon Sep 17 00:00:00 2001
From: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Date: Sun, 9 Apr 2023 14:53:18 -0400
Subject: [PATCH] gallium: Add u_default_get_sample_position

ctx->get_sample_position doesn't change what it returns based on the programmed
positions, it's just supposed to return the defaults. For most (all?) hardware,
those are the Vulkan standard sample positions. In bf9a1e0a4be ("zink: add a
pipe_context::get_sample_position hook"), Mike wondered why there wasn't a
common implementation. So here's one to fix that :~)

Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Reviewed-by: Mike Blumenkrantz <michael.blumenkrantz@gmail.com>
Reviewed-by: Emma Anholt <emma@anholt.net>
Reviewed-by: Jesse Natalie <jenatali@microsoft.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/22383>
---
 src/gallium/auxiliary/meson.build             |  2 +
 .../auxiliary/util/u_sample_positions.c       | 86 +++++++++++++++++++
 .../auxiliary/util/u_sample_positions.h       | 25 ++++++
 3 files changed, 113 insertions(+)
 create mode 100644 src/gallium/auxiliary/util/u_sample_positions.c
 create mode 100644 src/gallium/auxiliary/util/u_sample_positions.h

diff --git a/src/gallium/auxiliary/meson.build b/src/gallium/auxiliary/meson.build
index 3d7ec917e49..2080ffae5f2 100644
--- a/src/gallium/auxiliary/meson.build
+++ b/src/gallium/auxiliary/meson.build
@@ -251,6 +251,8 @@ files_libgallium = files(
   'util/u_rect.h',
   'util/u_resource.c',
   'util/u_resource.h',
+  'util/u_sample_positions.c',
+  'util/u_sample_positions.h',
   'util/u_sampler.c',
   'util/u_sampler.h',
   'util/u_screen.c',
diff --git a/src/gallium/auxiliary/util/u_sample_positions.c b/src/gallium/auxiliary/util/u_sample_positions.c
new file mode 100644
index 00000000000..a96e8c038cc
--- /dev/null
+++ b/src/gallium/auxiliary/util/u_sample_positions.c
@@ -0,0 +1,86 @@
+/*
+ * Copyright 2023 Alyssa Rosenzweig
+ * SPDX-License-Identifier: MIT
+ */
+
+#include "u_sample_positions.h"
+
+/*
+ * This file implement a default version of get_sample_position that returns the
+ * standard sample positions, as standardized in both Vulkan and Direct3D and
+ * hence almost everyone's hardware.
+ */
+
+static const float u_default_sample_positions_1x[][2] = {
+   {0.5, 0.5}
+};
+
+static const float u_default_sample_positions_2x[][2] = {
+   {0.75, 0.75},
+   {0.25, 0.25}
+};
+
+static const float u_default_sample_positions_4x[][4] = {
+   {0.375, 0.125},
+   {0.875, 0.375},
+   {0.125, 0.625},
+   {0.625, 0.875},
+};
+
+static const float u_default_sample_positions_8x[][4] = {
+   {0.5625, 0.3125},
+   {0.4375, 0.6875},
+   {0.8125, 0.5625},
+   {0.3125, 0.1875},
+   {0.1875, 0.8125},
+   {0.0625, 0.4375},
+   {0.6875, 0.9375},
+   {0.9375, 0.0625},
+
+};
+
+static const float u_default_sample_positions_16x[][4] = {
+   {0.5625, 0.5625},
+   {0.4375, 0.3125},
+   {0.3125, 0.625},
+   {0.75,   0.4375},
+   {0.1875, 0.375},
+   {0.625,  0.8125},
+   {0.8125, 0.6875},
+   {0.6875, 0.1875},
+   {0.375,  0.875},
+   {0.5,    0.0625},
+   {0.25,   0.125},
+   {0.125,  0.75},
+   {0.0,    0.5},
+   {0.9375, 0.25},
+   {0.875,  0.9375},
+   {0.0625, 0.0},
+};
+
+static const float *
+u_default_sample_position(unsigned sample_count, unsigned sample_index)
+{
+   switch (sample_count) {
+   case  0:
+   case  1: return u_default_sample_positions_1x[sample_index];
+   case  2: return u_default_sample_positions_2x[sample_index];
+   case  4: return u_default_sample_positions_4x[sample_index];
+   case  8: return u_default_sample_positions_8x[sample_index];
+   case 16: return u_default_sample_positions_16x[sample_index];
+   default: unreachable("Invalid sample count");
+   }
+}
+
+void
+u_default_get_sample_position(struct pipe_context *ctx,
+                              unsigned sample_count,
+                              unsigned sample_index,
+                              float *out_value)
+{
+   const float *positions =
+      u_default_sample_position(sample_count, sample_index);
+
+   out_value[0] = positions[0];
+   out_value[1] = positions[1];
+}
diff --git a/src/gallium/auxiliary/util/u_sample_positions.h b/src/gallium/auxiliary/util/u_sample_positions.h
new file mode 100644
index 00000000000..aea3c20f702
--- /dev/null
+++ b/src/gallium/auxiliary/util/u_sample_positions.h
@@ -0,0 +1,25 @@
+/*
+ * Copyright 2023 Alyssa Rosenzweig
+ * SPDX-License-Identifier: MIT
+ */
+
+#ifndef U_SAMPLE_POSITIONS_H
+#define U_SAMPLE_POSITIONS_H
+
+#include "pipe/p_context.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+void
+u_default_get_sample_position(struct pipe_context *ctx,
+                              unsigned sample_count,
+                              unsigned sample_index,
+                              float *out_value);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif