LibDraw: Introduce (formerly known as SharedGraphics.)

Instead of LibGUI and WindowServer building their own copies of the drawing
and graphics code, let's it in a separate LibDraw library.

This avoids building the code twice, and will encourage better separation
of concerns. :^)

Libraries/LibDraw/Color.h

@@ -0,0 +1,143 @@
+#pragma once
+
+#include <AK/AKString.h>
+#include <AK/Types.h>
+
+typedef u32 RGBA32;
+
+inline constexpr u32 make_rgb(u8 r, u8 g, u8 b)
+{
+    return ((r << 16) | (g << 8) | b);
+}
+
+class Color {
+public:
+    enum NamedColor {
+        Black,
+        White,
+        Red,
+        Green,
+        Cyan,
+        Blue,
+        Yellow,
+        Magenta,
+        DarkGray,
+        MidGray,
+        LightGray,
+        WarmGray,
+        DarkGreen,
+        DarkBlue,
+        DarkRed,
+        MidGreen,
+        MidRed,
+        MidBlue,
+        MidMagenta,
+    };
+
+    Color() {}
+    Color(NamedColor);
+    Color(u8 r, u8 g, u8 b)
+        : m_value(0xff000000 | (r << 16) | (g << 8) | b)
+    {
+    }
+    Color(u8 r, u8 g, u8 b, u8 a)
+        : m_value((a << 24) | (r << 16) | (g << 8) | b)
+    {
+    }
+
+    static Color from_rgb(unsigned rgb) { return Color(rgb | 0xff000000); }
+    static Color from_rgba(unsigned rgba) { return Color(rgba); }
+
+    u8 red() const { return (m_value >> 16) & 0xff; }
+    u8 green() const { return (m_value >> 8) & 0xff; }
+    u8 blue() const { return m_value & 0xff; }
+    u8 alpha() const { return (m_value >> 24) & 0xff; }
+
+    void set_alpha(u8 value)
+    {
+        m_value &= 0x00ffffff;
+        m_value |= value << 24;
+    }
+
+    void set_red(u8 value)
+    {
+        m_value &= 0xff00ffff;
+        m_value |= value << 16;
+    }
+
+    void set_green(u8 value)
+    {
+        m_value &= 0xffff00ff;
+        m_value |= value << 8;
+    }
+
+    void set_blue(u8 value)
+    {
+        m_value &= 0xffffff00;
+        m_value |= value;
+    }
+
+    Color with_alpha(u8 alpha)
+    {
+        return Color((m_value & 0x00ffffff) | alpha << 24);
+    }
+
+    Color blend(Color source) const
+    {
+        if (!alpha() || source.alpha() == 255)
+            return source;
+
+        if (!source.alpha())
+            return *this;
+
+        int d = 255 * (alpha() + source.alpha()) - alpha() * source.alpha();
+        u8 r = (red() * alpha() * (255 - source.alpha()) + 255 * source.alpha() * source.red()) / d;
+        u8 g = (green() * alpha() * (255 - source.alpha()) + 255 * source.alpha() * source.green()) / d;
+        u8 b = (blue() * alpha() * (255 - source.alpha()) + 255 * source.alpha() * source.blue()) / d;
+        u8 a = d / 255;
+        return Color(r, g, b, a);
+    }
+
+    Color to_grayscale() const
+    {
+        int gray = (red() + green() + blue()) / 3;
+        return Color(gray, gray, gray, alpha());
+    }
+
+    Color darkened(float amount = 0.5) const
+    {
+        return Color(red() * amount, green() * amount, blue() * amount, alpha());
+    }
+
+    Color lightened() const
+    {
+        return Color(min(255.0, red() * 1.2), min(255.0, green() * 1.2), min(255.0, blue() * 1.2), alpha());
+    }
+
+    Color inverted() const
+    {
+        return Color(~red(), ~green(), ~blue());
+    }
+
+    RGBA32 value() const { return m_value; }
+
+    bool operator==(const Color& other) const
+    {
+        return m_value == other.m_value;
+    }
+
+    bool operator!=(const Color& other) const
+    {
+        return m_value != other.m_value;
+    }
+
+    String to_string() const;
+
+private:
+    explicit Color(RGBA32 rgba)
+        : m_value(rgba)
+    {
+    }
+
+    RGBA32 m_value { 0 };
+};