From c98d92a4c4d97e8118bc3ad122b500e16aefa5f2 Mon Sep 17 00:00:00 2001
From: ISSOtm <eldredhabert0@gmail.com>
Date: Sun, 6 Mar 2022 13:35:19 +0100
Subject: [PATCH] Implement `-C`

---
 src/gfx/rgba.cpp | 34 +++++++++++++++++++++++++++++++---
 1 file changed, 31 insertions(+), 3 deletions(-)

diff --git a/src/gfx/rgba.cpp b/src/gfx/rgba.cpp
index 63b5b5aa..0902ebd5 100644
--- a/src/gfx/rgba.cpp
+++ b/src/gfx/rgba.cpp
@@ -6,15 +6,43 @@
 
 #include "gfx/main.hpp" // options
 
+/*
+ * based on the Gaussian-like curve used by SameBoy since commit
+ * 65dd02cc52f531dbbd3a7e6014e99d5b24e71a4c (Oct 2017)
+ * with ties resolved by comparing the difference of the squares.
+ */
+static std::array<uint8_t, 256> reverse_curve{
+	0,  0,  1,  1,  2,  2,  3,  3,  3,  3,  4,  4,  4,  4,  4,  4, // These
+	5,  5,  5,  5,  5,  5,  6,  6,  6,  6,  6,  6,  6,  6,  7,  7, // comments
+	7,  7,  7,  7,  7,  7,  7,  8,  8,  8,  8,  8,  8,  8,  8,  8, // prevent
+	9,  9,  9,  9,  9,  9,  9,  9,  9,  9,  10, 10, 10, 10, 10, 10, // clang-format
+	10, 10, 10, 10, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, // from
+	12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 13, 13, 13, 13, // reflowing
+	13, 13, 13, 13, 13, 13, 13, 13, 14, 14, 14, 14, 14, 14, 14, 14, // these
+	14, 14, 14, 14, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, // 16
+	16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 16, 17, 17, 17, // 16-iterm
+	17, 17, 17, 17, 17, 17, 17, 17, 17, 18, 18, 18, 18, 18, 18, 18, // lines,
+	18, 18, 18, 18, 18, 19, 19, 19, 19, 19, 19, 19, 19, 19, 19, 19, // which,
+	19, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 21, 21, 21, 21, // in
+	21, 21, 21, 21, 21, 21, 21, 22, 22, 22, 22, 22, 22, 22, 22, 22, // my
+	22, 23, 23, 23, 23, 23, 23, 23, 23, 23, 24, 24, 24, 24, 24, 24, // opinion,
+	24, 24, 25, 25, 25, 25, 25, 25, 25, 25, 26, 26, 26, 26, 26, 26, // help
+	26, 27, 27, 27, 27, 27, 28, 28, 28, 28, 29, 29, 29, 30, 30, 31, // visualization!
+};
+
 uint16_t Rgba::cgbColor() const {
 	if (isTransparent()) {
 		return transparent;
 	}
+
+	uint8_t r = red, g = green, b = blue;
 	if (options.useColorCurve) {
-		assert(!"TODO");
-	} else {
-		return (red >> 3) | (green >> 3) << 5 | (blue >> 3) << 10;
+		g = g * 4 < b ? 0 : (g * 4 - b) / 3;
+		r = reverse_curve[r];
+		g = reverse_curve[g];
+		b = reverse_curve[b];
 	}
+	return (r >> 3) | (g >> 3) << 5 | (b >> 3) << 10;
 }
 
 uint8_t Rgba::grayIndex() const {