From 3d172bca0ee034edb261958f6d93407a621531a5 Mon Sep 17 00:00:00 2001
From: Jojo-1000 <33495614+Jojo-1000@users.noreply.github.com>
Date: Tue, 16 Mar 2021 21:14:43 +0100
Subject: [PATCH] Add conversion from RGB to HueSaturation.

---
 include/hueplusplus/ColorUnits.h | 12 +++++++++---
 src/ColorUnits.cpp               | 42 ++++++++++++++++++++++++++++++++++++++++--
 test/test_ColorUnits.cpp         | 35 +++++++++++++++++++++++++++++++----
 3 files changed, 80 insertions(+), 9 deletions(-)

diff --git a/include/hueplusplus/ColorUnits.h b/include/hueplusplus/ColorUnits.h
index eb26991..077e08c 100644
--- a/include/hueplusplus/ColorUnits.h
+++ b/include/hueplusplus/ColorUnits.h
@@ -126,6 +126,12 @@ struct RGB
     //!
     //! Performs gamma correction so the light color matches the screen color better.
     XYBrightness toXY(const ColorGamut& gamut) const;
+
+    //! \brief Convert to HueSaturation
+    //!
+    //! To get the correct color, set brightness to max(r,g,b).
+    HueSaturation toHueSaturation() const;
+
     //! \brief Create from XYBrightness
     //!
     //! Performs gamma correction so the light color matches the screen color better.
@@ -143,9 +149,9 @@ struct RGB
 };
 
 //! \brief Const function that converts Kelvin to Mired.
-    //!
-    //! \param kelvin Unsigned integer value in Kelvin
-    //! \return Unsigned integer value in Mired
+//!
+//! \param kelvin Unsigned integer value in Kelvin
+//! \return Unsigned integer value in Mired
 unsigned int kelvinToMired(unsigned int kelvin);
 
 //! \brief Const function that converts Mired to Kelvin.
diff --git a/src/ColorUnits.cpp b/src/ColorUnits.cpp
index be65b21..2d12719 100644
--- a/src/ColorUnits.cpp
+++ b/src/ColorUnits.cpp
@@ -142,17 +142,55 @@ XYBrightness RGB::toXY(const ColorGamut& gamut) const
     return xy;
 }
 
+HueSaturation RGB::toHueSaturation() const
+{
+    const uint8_t cmax = std::max(r, std::max(g, b));
+    const uint8_t cmin = std::min(r, std::min(g, b));
+    const float diff = cmax - cmin;
+
+    int h = -1;
+    int s = -1;
+
+    if (cmax == cmin)
+    {
+        h = 0;
+    }
+    else if (cmax == r)
+    {
+        h = (int)(9307 * ((g - b) / diff) + 65535) % 65535;
+    }
+    else if (cmax == g)
+    {
+        h = (int)(12750 * ((b - r) / diff) + 25500) % 65535;
+    }
+    else if (cmax == b)
+    {
+        h = (int)(10710 * ((r - g) / diff) + 46920) % 65535;
+    }
+
+    if (cmax == 0)
+    {
+        s = 0;
+    }
+    else
+    {
+        s = std::round((diff / cmax) * 254);
+    }
+
+    return {h, s};
+}
+
 RGB RGB::fromXY(const XYBrightness& xy)
 {
     if (xy.brightness < 1e-4)
     {
-        return RGB{ 0,0,0 };
+        return RGB {0, 0, 0};
     }
     const float z = 1.f - xy.xy.x - xy.xy.y;
     // use a fixed luminosity and rescale the resulting rgb values using brightness
     // randomly sampled conversions shown a minimum difference between original values
     // and values after rgb -> xy -> rgb conversion for Y = 0.3
-    // (r-r')^2, (g-g')^2, (b-b')^2: 
+    // (r-r')^2, (g-g')^2, (b-b')^2:
     // 4.48214,  4.72039,  3.12141
     // Max. Difference:
     // 9,        9,        8
diff --git a/test/test_ColorUnits.cpp b/test/test_ColorUnits.cpp
index 6e89329..bd81f1f 100644
--- a/test/test_ColorUnits.cpp
+++ b/test/test_ColorUnits.cpp
@@ -108,7 +108,7 @@ TEST(RGB, toXY)
         EXPECT_FLOAT_EQ(xy.brightness, 1.f);
     }
     {
-        const RGB black{ 0,0,0 };
+        const RGB black {0, 0, 0};
         XYBrightness xy = black.toXY(gamut::maxGamut);
         EXPECT_FLOAT_EQ(xy.xy.x, 0.32272673f);
         EXPECT_FLOAT_EQ(xy.xy.y, 0.32902291f);
@@ -116,6 +116,34 @@ TEST(RGB, toXY)
     }
 }
 
+TEST(RGB, toHueSaturation)
+{
+    {
+        const RGB red {255, 0, 0};
+        HueSaturation hs = red.toHueSaturation();
+        EXPECT_EQ(0, hs.hue);
+        EXPECT_EQ(254, hs.saturation);
+    }
+    {
+        const RGB darkGreen{64, 128, 128 };
+        HueSaturation hs = darkGreen.toHueSaturation();
+        EXPECT_EQ(38250, hs.hue);
+        EXPECT_EQ(127, hs.saturation);
+    }
+    {
+        const RGB white {255, 255, 255};
+        HueSaturation hs = white.toHueSaturation();
+        EXPECT_EQ(0, hs.hue);
+        EXPECT_EQ(0, hs.saturation);
+    }
+    {
+        const RGB black {0, 0, 0};
+        HueSaturation hs = black.toHueSaturation();
+        EXPECT_EQ(0, hs.hue);
+        EXPECT_EQ(0, hs.saturation);
+    }
+}
+
 TEST(RGB, fromXY)
 {
     {
@@ -130,7 +158,7 @@ TEST(RGB, fromXY)
         EXPECT_FLOAT_EQ(xyRed.brightness, reversed.brightness);
     }
     {
-        const XYBrightness xyWhite{ {0.32272673f, 0.32902291f}, 1.f };
+        const XYBrightness xyWhite {{0.32272673f, 0.32902291f}, 1.f};
         const RGB white = RGB::fromXY(xyWhite);
         EXPECT_EQ(255, white.r);
         EXPECT_EQ(255, white.g);
@@ -143,7 +171,7 @@ TEST(RGB, fromXY)
     {
         const XYBrightness xyRed {{0.70060623f, 0.299301f}, 1.f};
         const RGB red = RGB::fromXY(xyRed, gamut::gamutB);
-        const RGB red2 = RGB::fromXY({ gamut::gamutB.corrected(xyRed.xy), xyRed.brightness });
+        const RGB red2 = RGB::fromXY({gamut::gamutB.corrected(xyRed.xy), xyRed.brightness});
         EXPECT_EQ(red2.r, red.r);
         EXPECT_EQ(red2.g, red.g);
         EXPECT_EQ(red2.b, red.b);
@@ -186,7 +214,6 @@ TEST(RGB, fromXY)
     EXPECT_LE(maxDiffR, 81);
     EXPECT_LE(maxDiffG, 81);
     EXPECT_LE(maxDiffB, 64);
-
 }
 
 TEST(ColorUnits, kelvinToMired)
--
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