From 7a1464d783742512fdc6e0a083ffadd0ce63c1b4 Mon Sep 17 00:00:00 2001
From: HybridDog <3192173+HybridDog@users.noreply.github.com>
Date: Fri, 26 Nov 2021 19:30:49 +0100
Subject: [PATCH] Minimap: gamma-correct average texture colour calculation
 (#9249)

This calculates the average texture colour while heeding the sRGB colourspace.
---
 src/client/tile.cpp | 55 +++++++++++++++++++++++++++++++++++++--------
 1 file changed, 46 insertions(+), 9 deletions(-)

diff --git a/src/client/tile.cpp b/src/client/tile.cpp
index 2f57503d3..da03ff5c8 100644
--- a/src/client/tile.cpp
+++ b/src/client/tile.cpp
@@ -2229,6 +2229,48 @@ video::ITexture* TextureSource::getNormalTexture(const std::string &name)
 	return NULL;
 }
 
+namespace {
+	// For more colourspace transformations, see for example
+	// https://github.com/tobspr/GLSL-Color-Spaces/blob/master/ColorSpaces.inc.glsl
+
+	inline float linear_to_srgb_component(float v)
+	{
+		if (v > 0.0031308f)
+			return 1.055f * powf(v, 1.0f / 2.4f) - 0.055f;
+		return 12.92f * v;
+	}
+	inline float srgb_to_linear_component(float v)
+	{
+		if (v > 0.04045f)
+			return powf((v + 0.055f) / 1.055f, 2.4f);
+		return v / 12.92f;
+	}
+
+	v3f srgb_to_linear(const video::SColor &col_srgb)
+	{
+		v3f col(col_srgb.getRed(), col_srgb.getGreen(), col_srgb.getBlue());
+		col /= 255.0f;
+		col.X = srgb_to_linear_component(col.X);
+		col.Y = srgb_to_linear_component(col.Y);
+		col.Z = srgb_to_linear_component(col.Z);
+		return col;
+	}
+
+	video::SColor linear_to_srgb(const v3f &col_linear)
+	{
+		v3f col;
+		col.X = linear_to_srgb_component(col_linear.X);
+		col.Y = linear_to_srgb_component(col_linear.Y);
+		col.Z = linear_to_srgb_component(col_linear.Z);
+		col *= 255.0f;
+		col.X = core::clamp<float>(col.X, 0.0f, 255.0f);
+		col.Y = core::clamp<float>(col.Y, 0.0f, 255.0f);
+		col.Z = core::clamp<float>(col.Z, 0.0f, 255.0f);
+		return video::SColor(0xff, myround(col.X), myround(col.Y),
+			myround(col.Z));
+	}
+}
+
 video::SColor TextureSource::getTextureAverageColor(const std::string &name)
 {
 	video::IVideoDriver *driver = RenderingEngine::get_video_driver();
@@ -2243,9 +2285,7 @@ video::SColor TextureSource::getTextureAverageColor(const std::string &name)
 		return c;
 
 	u32 total = 0;
-	u32 tR = 0;
-	u32 tG = 0;
-	u32 tB = 0;
+	v3f col_acc(0, 0, 0);
 	core::dimension2d<u32> dim = image->getDimension();
 	u16 step = 1;
 	if (dim.Width > 16)
@@ -2255,17 +2295,14 @@ video::SColor TextureSource::getTextureAverageColor(const std::string &name)
 			c = image->getPixel(x,y);
 			if (c.getAlpha() > 0) {
 				total++;
-				tR += c.getRed();
-				tG += c.getGreen();
-				tB += c.getBlue();
+				col_acc += srgb_to_linear(c);
 			}
 		}
 	}
 	image->drop();
 	if (total > 0) {
-		c.setRed(tR / total);
-		c.setGreen(tG / total);
-		c.setBlue(tB / total);
+		col_acc /= total;
+		c = linear_to_srgb(col_acc);
 	}
 	c.setAlpha(255);
 	return c;