PixelPaint+LibGfx: Add sepia color filter

Userland/Libraries/LibGfx/Color.h

@@ -232,6 +232,33 @@ public:
         return Color(gray, gray, gray, alpha());
     }
 
+    constexpr Color sepia(float amount = 1.0f) const
+    {
+        auto blend_factor = 1.0f - amount;
+
+        auto r1 = 0.393f + 0.607f * blend_factor;
+        auto r2 = 0.769f - 0.769f * blend_factor;
+        auto r3 = 0.189f - 0.189f * blend_factor;
+
+        auto g1 = 0.349f - 0.349f * blend_factor;
+        auto g2 = 0.686f + 0.314f * blend_factor;
+        auto g3 = 0.168f - 0.168f * blend_factor;
+
+        auto b1 = 0.272f - 0.272f * blend_factor;
+        auto b2 = 0.534f - 0.534f * blend_factor;
+        auto b3 = 0.131f + 0.869f * blend_factor;
+
+        auto r = red();
+        auto g = green();
+        auto b = blue();
+
+        return Color(
+            clamp(lroundf(r * r1 + g * r2 + b * r3), 0, 255),
+            clamp(lroundf(r * g1 + g * g2 + b * g3), 0, 255),
+            clamp(lroundf(r * b1 + g * b2 + b * b3), 0, 255),
+            alpha());
+    }
+
     constexpr Color darkened(float amount = 0.5f) const
     {
         return Color(red() * amount, green() * amount, blue() * amount, alpha());

Userland/Libraries/LibGfx/Filters/SepiaFilter.h

@@ -0,0 +1,32 @@
+/*
+ * Copyright (c) 2022, Xavier Defrang <xavier.defrang@gmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/StdLibExtras.h>
+#include <LibGfx/Filters/ColorFilter.h>
+#include <math.h>
+
+namespace Gfx {
+
+class SepiaFilter : public ColorFilter {
+public:
+    SepiaFilter(float amount = 1.0f)
+        : m_amount(amount)
+    {
+    }
+    virtual ~SepiaFilter() { }
+
+    virtual char const* class_name() const override { return "SepiaFilter"; }
+
+protected:
+    Color convert_color(Color original) override { return original.sepia(m_amount); };
+
+private:
+    float m_amount;
+};
+
+}