video_core/texture: Use a LUT to convert sRGB texture borders

This is a reversed look up table extracted from
https://gist.github.com/rygorous/2203834#file-gistfile1-cpp-L41-L62

that is used in
https://github.com/devkitPro/deko3d/blob/04d4e9e587fa3dc5447b43d273bc45f440226e41/source/maxwell/tsc_generate.cpp#L38

Games usually bind 0xFD expecting a float texture border of 1.0f.
The conversion previous to this commit was multiplying the uint8 sRGB
texture border color by 255. This is close to 1.0f but when that
difference matters, some graphical glitches appear.

This look up table is manually changed in the edges, clamping towards
0.0f and 1.0f.

While we are at it, move this logic to its own translation unit.

3 files changed, 61 insertions, 9 deletions

diff --git a/src/video_core/CMakeLists.txt b/src/video_core/CMakeLists.txt
index effe76a63..f7febd6a2 100644
--- a/src/video_core/CMakeLists.txt
+++ b/src/video_core/CMakeLists.txt
@@ -148,6 +148,7 @@ add_library(video_core STATIC
     textures/convert.h
     textures/decoders.cpp
     textures/decoders.h
+    textures/texture.cpp
     textures/texture.h
     video_core.cpp
     video_core.h
diff --git a/src/video_core/textures/texture.cpp b/src/video_core/textures/texture.cpp
new file mode 100644
index 000000000..b1417db1e
--- /dev/null
+++ b/src/video_core/textures/texture.cpp
@@ -0,0 +1,58 @@
+// Copyright 2020 yuzu Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#include <array>
+
+#include "video_core/textures/texture.h"
+
+namespace Tegra::Texture {
+
+namespace {
+
+constexpr std::array<float, 256> SRGB_CONVERSION_LUT = {
+    0.000000f, 0.000000f, 0.000000f, 0.000012f, 0.000021f, 0.000033f, 0.000046f, 0.000062f,
+    0.000081f, 0.000102f, 0.000125f, 0.000151f, 0.000181f, 0.000214f, 0.000251f, 0.000293f,
+    0.000338f, 0.000388f, 0.000443f, 0.000503f, 0.000568f, 0.000639f, 0.000715f, 0.000798f,
+    0.000887f, 0.000983f, 0.001085f, 0.001195f, 0.001312f, 0.001437f, 0.001569f, 0.001710f,
+    0.001860f, 0.002019f, 0.002186f, 0.002364f, 0.002551f, 0.002748f, 0.002955f, 0.003174f,
+    0.003403f, 0.003643f, 0.003896f, 0.004160f, 0.004436f, 0.004725f, 0.005028f, 0.005343f,
+    0.005672f, 0.006015f, 0.006372f, 0.006744f, 0.007130f, 0.007533f, 0.007950f, 0.008384f,
+    0.008834f, 0.009301f, 0.009785f, 0.010286f, 0.010805f, 0.011342f, 0.011898f, 0.012472f,
+    0.013066f, 0.013680f, 0.014313f, 0.014967f, 0.015641f, 0.016337f, 0.017054f, 0.017793f,
+    0.018554f, 0.019337f, 0.020144f, 0.020974f, 0.021828f, 0.022706f, 0.023609f, 0.024536f,
+    0.025489f, 0.026468f, 0.027473f, 0.028504f, 0.029563f, 0.030649f, 0.031762f, 0.032904f,
+    0.034074f, 0.035274f, 0.036503f, 0.037762f, 0.039050f, 0.040370f, 0.041721f, 0.043103f,
+    0.044518f, 0.045964f, 0.047444f, 0.048956f, 0.050503f, 0.052083f, 0.053699f, 0.055349f,
+    0.057034f, 0.058755f, 0.060513f, 0.062307f, 0.064139f, 0.066008f, 0.067915f, 0.069861f,
+    0.071845f, 0.073869f, 0.075933f, 0.078037f, 0.080182f, 0.082369f, 0.084597f, 0.086867f,
+    0.089180f, 0.091535f, 0.093935f, 0.096378f, 0.098866f, 0.101398f, 0.103977f, 0.106601f,
+    0.109271f, 0.111988f, 0.114753f, 0.117565f, 0.120426f, 0.123335f, 0.126293f, 0.129301f,
+    0.132360f, 0.135469f, 0.138629f, 0.141841f, 0.145105f, 0.148421f, 0.151791f, 0.155214f,
+    0.158691f, 0.162224f, 0.165810f, 0.169453f, 0.173152f, 0.176907f, 0.180720f, 0.184589f,
+    0.188517f, 0.192504f, 0.196549f, 0.200655f, 0.204820f, 0.209046f, 0.213334f, 0.217682f,
+    0.222093f, 0.226567f, 0.231104f, 0.235704f, 0.240369f, 0.245099f, 0.249894f, 0.254754f,
+    0.259681f, 0.264674f, 0.269736f, 0.274864f, 0.280062f, 0.285328f, 0.290664f, 0.296070f,
+    0.301546f, 0.307094f, 0.312713f, 0.318404f, 0.324168f, 0.330006f, 0.335916f, 0.341902f,
+    0.347962f, 0.354097f, 0.360309f, 0.366597f, 0.372961f, 0.379403f, 0.385924f, 0.392524f,
+    0.399202f, 0.405960f, 0.412798f, 0.419718f, 0.426719f, 0.433802f, 0.440967f, 0.448216f,
+    0.455548f, 0.462965f, 0.470465f, 0.478052f, 0.485725f, 0.493484f, 0.501329f, 0.509263f,
+    0.517285f, 0.525396f, 0.533595f, 0.541885f, 0.550265f, 0.558736f, 0.567299f, 0.575954f,
+    0.584702f, 0.593542f, 0.602477f, 0.611507f, 0.620632f, 0.629852f, 0.639168f, 0.648581f,
+    0.658092f, 0.667700f, 0.677408f, 0.687214f, 0.697120f, 0.707127f, 0.717234f, 0.727443f,
+    0.737753f, 0.748167f, 0.758685f, 0.769305f, 0.780031f, 0.790861f, 0.801798f, 0.812839f,
+    0.823989f, 0.835246f, 0.846611f, 0.858085f, 0.869668f, 0.881360f, 0.893164f, 0.905078f,
+    0.917104f, 0.929242f, 0.941493f, 0.953859f, 0.966338f, 1.000000f, 1.000000f, 1.000000f,
+};
+
+} // Anonymous namespace
+
+std::array<float, 4> TSCEntry::GetBorderColor() const noexcept {
+    if (!srgb_conversion) {
+        return border_color;
+    }
+    return {SRGB_CONVERSION_LUT[srgb_border_color_r], SRGB_CONVERSION_LUT[srgb_border_color_g],
+            SRGB_CONVERSION_LUT[srgb_border_color_b], border_color[3]};
+}
+
+} // namespace Tegra::Texture
diff --git a/src/video_core/textures/texture.h b/src/video_core/textures/texture.h
index 7edc4abe1..262cd3cc1 100644
--- a/src/video_core/textures/texture.h
+++ b/src/video_core/textures/texture.h
@@ -336,6 +336,8 @@ struct TSCEntry {
         std::array<u8, 0x20> raw;
     };
 
+    std::array<float, 4> GetBorderColor() const noexcept;
+
     float GetMaxAnisotropy() const {
         const u32 min_value = [] {
             switch (static_cast<Anisotropy>(Settings::values.max_anisotropy)) {
@@ -368,15 +370,6 @@ struct TSCEntry {
         constexpr u32 mask = 1U << (13 - 1);
         return static_cast<float>(static_cast<s32>((mip_lod_bias ^ mask) - mask)) / 256.0f;
     }
-
-    std::array<float, 4> GetBorderColor() const {
-        if (srgb_conversion) {
-            return {static_cast<float>(srgb_border_color_r) / 255.0f,
-                    static_cast<float>(srgb_border_color_g) / 255.0f,
-                    static_cast<float>(srgb_border_color_b) / 255.0f, border_color[3]};
-        }
-        return border_color;
-    }
 };
 static_assert(sizeof(TSCEntry) == 0x20, "TSCEntry has wrong size");