From 0bfe178650db439b575cc83aad81598ed40d8dc3 Mon Sep 17 00:00:00 2001
From: TiKevin83 <38826675+TiKevin83@users.noreply.github.com>
Date: Wed, 8 Apr 2020 19:19:18 -0400
Subject: [PATCH] New GBC LCD correction for Gambatte palette from documented
 shader research
 https://forums.libretro.com/t/real-gba-and-ds-phat-colors/1540 (#1917)

---
 .../Consoles/Nintendo/Gameboy/GBColors.cs            | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/BizHawk.Emulation.Cores/Consoles/Nintendo/Gameboy/GBColors.cs b/BizHawk.Emulation.Cores/Consoles/Nintendo/Gameboy/GBColors.cs
index c44dab34c2..e262387370 100644
--- a/BizHawk.Emulation.Cores/Consoles/Nintendo/Gameboy/GBColors.cs
+++ b/BizHawk.Emulation.Cores/Consoles/Nintendo/Gameboy/GBColors.cs
@@ -51,9 +51,15 @@ namespace BizHawk.Emulation.Cores.Nintendo.Gameboy
 		public static Triple GambatteColor(Triple c)
 		{
 			Triple ret;
-			ret.r = (c.r * 13 + c.g * 2 + c.b) >> 1;
-			ret.g = (c.g * 3 + c.b) << 1;
-			ret.b = (c.r * 3 + c.g * 2 + c.b * 11) >> 1;
+			double gammaR = Math.Pow((double)c.r / 31, 2.2);
+			double gammaG = Math.Pow((double)c.g / 31, 2.2);
+			double gammaB = Math.Pow((double)c.b / 31, 2.2);
+			ret.r = (int)(Math.Pow(gammaR * .87 + gammaG * .18 - gammaB * .05, 1/ 2.2) * 255 + .5);
+			ret.g = (int)(Math.Pow(gammaG * .66 + gammaR * .115 + gammaB * .225, 1/ 2.2) * 255 + .5);
+			ret.b = (int)(Math.Pow(gammaB * .79 + gammaR * .14 + gammaG * .07, 1/ 2.2) * 255 + .5);
+			ret.r = Math.Max(0, Math.Min(255, ret.r));
+			ret.g = Math.Max(0, Math.Min(255, ret.g));
+			ret.b = Math.Max(0, Math.Min(255, ret.b));
 			return ret;
 		}