// Copyright (c) Xenko contributors (https://xenko.com) and Silicon Studio Corp. (https://www.siliconstudio.co.jp)
// Distributed under the MIT license. See the LICENSE.md file in the project root for more information.
//
// -----------------------------------------------------------------------------
// Original code from SlimMath project. http://code.google.com/p/slimmath/
// Greetings to SlimDX Group. Original code published with the following license:
// -----------------------------------------------------------------------------
/*
* Copyright (c) 2007-2011 SlimDX Group
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
using System;
using System.Globalization;
using System.Runtime.InteropServices;
using System.Runtime.Serialization;

namespace math
{
    /// <summary>
    /// Represents a color in the form of rgba.
    /// </summary>
    [DataContract( Name = "Color4" )]
    [DataStyle( DataStyle.Compact )]
    [StructLayout( LayoutKind.Sequential, Pack = 4 )]
    public struct Color4 : IEquatable<Color4>, IFormattable
    {
        private const string ToStringFormat = "A:{0} R:{1} G:{2} B:{3}";

        /// <summary>
        /// The Black color (0, 0, 0, 1).
        /// </summary>
        public static readonly Color4 Black = new Color4( 0.0f, 0.0f, 0.0f, 1.0f );

        /// <summary>
        /// The White color (1, 1, 1, 1).
        /// </summary>
        public static readonly Color4 White = new Color4( 1.0f, 1.0f, 1.0f, 1.0f );

        /// <summary>
        /// The red component of the color.
        /// </summary>
        [DataMember( Order = 0 )]
        public float R;

        /// <summary>
        /// The green component of the color.
        /// </summary>
        [DataMember( Order = 1 )]
        public float G;

        /// <summary>
        /// The blue component of the color.
        /// </summary>
        [DataMember( Order = 2 )]
        public float B;

        /// <summary>
        /// The alpha component of the color.
        /// </summary>
        [DataMember( Order = 3 )]
        public float A;

        /// <summary>
        /// Initializes a new instance of the <see cref="Color4"/> struct.
        /// </summary>
        /// <param name="value">The value that will be assigned to all components.</param>
        public Color4( float value )
        {
            A = R = G = B = value;
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="Color4"/> struct.
        /// </summary>
        /// <param name="red">The red component of the color.</param>
        /// <param name="green">The green component of the color.</param>
        /// <param name="blue">The blue component of the color.</param>
        /// <param name="alpha">The alpha component of the color.</param>
        public Color4( float red, float green, float blue, float alpha )
        {
            R = red;
            G = green;
            B = blue;
            A = alpha;
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="Color4"/> struct.
        /// </summary>
        /// <param name="value">The red, green, blue, and alpha components of the color.</param>
        public Color4( Vec4 value )
        {
            R = value.X;
            G = value.Y;
            B = value.Z;
            A = value.W;
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="Color4"/> struct.
        /// </summary>
        /// <param name="value">The red, green, and blue components of the color.</param>
        /// <param name="alpha">The alpha component of the color.</param>
        public Color4( Vec3 value, float alpha )
        {
            R = value.X;
            G = value.Y;
            B = value.Z;
            A = alpha;
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="Color4"/> struct.
        /// </summary>
        /// <param name="rgba">A packed integer containing all four color components in RGBA order.</param>
        public Color4( uint rgba )
        {
            A = ( ( rgba >> 24 ) & 255 ) / 255.0f;
            B = ( ( rgba >> 16 ) & 255 ) / 255.0f;
            G = ( ( rgba >> 8 ) & 255 ) / 255.0f;
            R = ( rgba & 255 ) / 255.0f;
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="Color4"/> struct.
        /// </summary>
        /// <param name="rgba">A packed integer containing all four color components in RGBA order.</param>
        public Color4( int rgba )
        {
            A = ( ( rgba >> 24 ) & 255 ) / 255.0f;
            B = ( ( rgba >> 16 ) & 255 ) / 255.0f;
            G = ( ( rgba >> 8 ) & 255 ) / 255.0f;
            R = ( rgba & 255 ) / 255.0f;
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="Color4"/> struct.
        /// </summary>
        /// <param name="values">The values to assign to the red, green, blue, and alpha components of the color. This must be an array with four elements.</param>
        /// <exception cref="ArgumentNullException">Thrown when <paramref name="values"/> is <c>null</c>.</exception>
        /// <exception cref="ArgumentOutOfRangeException">Thrown when <paramref name="values"/> contains more or less than four elements.</exception>
        public Color4( float[] values )
        {
            if( values == null )
                throw new ArgumentNullException( nameof( values ) );
            if( values.Length != 4 )
                throw new ArgumentOutOfRangeException( nameof( values ), "There must be four and only four input values for Color4." );

            R = values[0];
            G = values[1];
            B = values[2];
            A = values[3];
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="Color4"/> struct.
        /// </summary>
        /// <param name="color"><see cref="Color3"/> used to initialize the color.</param>
        public Color4( Color3 color )
        {
            R = color.R;
            G = color.G;
            B = color.B;
            A = 1.0f;
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="Color4"/> struct.
        /// </summary>
        /// <param name="color"><see cref="Color"/> used to initialize the color.</param>
        public Color4( Color color )
        {
            R = color.R / 255.0f;
            G = color.G / 255.0f;
            B = color.B / 255.0f;
            A = color.A / 255.0f;
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="Color4"/> struct.
        /// </summary>
        /// <param name="color"><see cref="Color"/> used to initialize the color.</param>
        public Color4( ColorBGRA color )
        {
            R = color.R / 255.0f;
            G = color.G / 255.0f;
            B = color.B / 255.0f;
            A = color.A / 255.0f;
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="Color4"/> struct.
        /// </summary>
        /// <param name="color"><see cref="Color3"/> used to initialize the color.</param>
        /// <param name="alpha">The alpha component of the color.</param>
        public Color4( Color3 color, float alpha )
        {
            R = color.R;
            G = color.G;
            B = color.B;
            A = alpha;
        }

        /// <summary>
        /// Gets or sets the component at the specified index.
        /// </summary>
        /// <value>The value of the red, green, blue, and alpha components, depending on the index.</value>
        /// <param name="index">The index of the component to access. Use 0 for the alpha component, 1 for the red component, 2 for the green component, and 3 for the blue component.</param>
        /// <returns>The value of the component at the specified index.</returns>
        /// <exception cref="System.ArgumentOutOfRangeException">Thrown when the <paramref name="index"/> is out of the range [0, 3].</exception>
        public float this[int index]
        {
            get
            {
                switch( index )
                {
                    case 0:
                        return R;
                    case 1:
                        return G;
                    case 2:
                        return B;
                    case 3:
                        return A;
                }

                throw new ArgumentOutOfRangeException( nameof( index ), "Indices for Color4 run from 0 to 3, inclusive." );
            }

            set
            {
                switch( index )
                {
                    case 0:
                        R = value;
                        break;
                    case 1:
                        G = value;
                        break;
                    case 2:
                        B = value;
                        break;
                    case 3:
                        A = value;
                        break;
                    default:
                        throw new ArgumentOutOfRangeException( nameof( index ), "Indices for Color4 run from 0 to 3, inclusive." );
                }
            }
        }

        /// <summary>
        /// Converts the color into a packed integer.
        /// </summary>
        /// <returns>A packed integer containing all four color components.</returns>
        public int ToBgra()
        {
            uint a = (uint)( A * 255.0f ) & 255;
            uint r = (uint)( R * 255.0f ) & 255;
            uint g = (uint)( G * 255.0f ) & 255;
            uint b = (uint)( B * 255.0f ) & 255;

            uint value = b;
            value |= g << 8;
            value |= r << 16;
            value |= a << 24;

            return (int)value;
        }

        /// <summary>
        /// Converts the color into a packed integer.
        /// </summary>
        public void ToBgra( out byte r, out byte g, out byte b, out byte a )
        {
            a = (byte)( A * 255.0f );
            r = (byte)( R * 255.0f );
            g = (byte)( G * 255.0f );
            b = (byte)( B * 255.0f );
        }

        /// <summary>
        /// Converts the color into a packed integer.
        /// </summary>
        /// <returns>A packed integer containing all four color components.</returns>
        public int ToRgba()
        {
            uint a = (uint)( A * 255.0f ) & 255;
            uint r = (uint)( R * 255.0f ) & 255;
            uint g = (uint)( G * 255.0f ) & 255;
            uint b = (uint)( B * 255.0f ) & 255;

            uint value = r;
            value |= g << 8;
            value |= b << 16;
            value |= a << 24;

            return (int)value;
        }

        /// <summary>
        /// Converts the color into a three component vector.
        /// </summary>
        /// <returns>A three component vector containing the red, green, and blue components of the color.</returns>
        public Vec3 ToVector3()
        {
            return new Vec3( R, G, B );
        }

        /// <summary>
        /// Converts the color into a four component vector.
        /// </summary>
        /// <returns>A four component vector containing all four color components.</returns>
        public Vec4 ToVector4()
        {
            return new Vec4( R, G, B, A );
        }

        /// <summary>
        /// Creates an array containing the elements of the color.
        /// </summary>
        /// <returns>A four-element array containing the components of the color.</returns>
        public float[] ToArray()
        {
            return new[] { R, G, B, A };
        }

        /// <summary>
        /// Converts this color from linear space to sRGB space.
        /// </summary>
        /// <returns>A color3 in sRGB space.</returns>
        public Color4 ToSRgb()
        {
            return new Color4( MathUtil.LinearToSRgb( R ), MathUtil.LinearToSRgb( G ), MathUtil.LinearToSRgb( B ), A );
        }

        /// <summary>
        /// Converts this color from sRGB space to linear space.
        /// </summary>
        /// <returns>A color4 in linear space.</returns>
        public Color4 ToLinear()
        {
            return new Color4( MathUtil.SRgbToLinear( R ), MathUtil.SRgbToLinear( G ), MathUtil.SRgbToLinear( B ), A );
        }

        /// <summary>
        /// Adds two colors.
        /// </summary>
        /// <param name="left">The first color to add.</param>
        /// <param name="right">The second color to add.</param>
        /// <param name="result">When the method completes, completes the sum of the two colors.</param>
        public static void Add( ref Color4 left, ref Color4 right, out Color4 result )
        {
            result.A = left.A + right.A;
            result.R = left.R + right.R;
            result.G = left.G + right.G;
            result.B = left.B + right.B;
        }

        /// <summary>
        /// Adds two colors.
        /// </summary>
        /// <param name="left">The first color to add.</param>
        /// <param name="right">The second color to add.</param>
        /// <returns>The sum of the two colors.</returns>
        public static Color4 Add( Color4 left, Color4 right )
        {
            return new Color4( left.R + right.R, left.G + right.G, left.B + right.B, left.A + right.A );
        }

        /// <summary>
        /// Subtracts two colors.
        /// </summary>
        /// <param name="left">The first color to subtract.</param>
        /// <param name="right">The second color to subtract.</param>
        /// <param name="result">WHen the method completes, contains the difference of the two colors.</param>
        public static void Subtract( ref Color4 left, ref Color4 right, out Color4 result )
        {
            result.A = left.A - right.A;
            result.R = left.R - right.R;
            result.G = left.G - right.G;
            result.B = left.B - right.B;
        }

        /// <summary>
        /// Subtracts two colors.
        /// </summary>
        /// <param name="left">The first color to subtract.</param>
        /// <param name="right">The second color to subtract</param>
        /// <returns>The difference of the two colors.</returns>
        public static Color4 Subtract( Color4 left, Color4 right )
        {
            return new Color4( left.R - right.R, left.G - right.G, left.B - right.B, left.A - right.A );
        }

        /// <summary>
        /// Modulates two colors.
        /// </summary>
        /// <param name="left">The first color to modulate.</param>
        /// <param name="right">The second color to modulate.</param>
        /// <param name="result">When the method completes, contains the modulated color.</param>
        public static void Modulate( ref Color4 left, ref Color4 right, out Color4 result )
        {
            result.A = left.A * right.A;
            result.R = left.R * right.R;
            result.G = left.G * right.G;
            result.B = left.B * right.B;
        }

        /// <summary>
        /// Modulates two colors.
        /// </summary>
        /// <param name="left">The first color to modulate.</param>
        /// <param name="right">The second color to modulate.</param>
        /// <returns>The modulated color.</returns>
        public static Color4 Modulate( Color4 left, Color4 right )
        {
            return new Color4( left.R * right.R, left.G * right.G, left.B * right.B, left.A * right.A );
        }

        /// <summary>
        /// Scales a color.
        /// </summary>
        /// <param name="value">The color to scale.</param>
        /// <param name="scale">The amount by which to scale.</param>
        /// <param name="result">When the method completes, contains the scaled color.</param>
        public static void Scale( ref Color4 value, float scale, out Color4 result )
        {
            result.A = value.A * scale;
            result.R = value.R * scale;
            result.G = value.G * scale;
            result.B = value.B * scale;
        }

        /// <summary>
        /// Scales a color.
        /// </summary>
        /// <param name="value">The color to scale.</param>
        /// <param name="scale">The amount by which to scale.</param>
        /// <returns>The scaled color.</returns>
        public static Color4 Scale( Color4 value, float scale )
        {
            return new Color4( value.R * scale, value.G * scale, value.B * scale, value.A * scale );
        }

        /// <summary>
        /// Negates a color.
        /// </summary>
        /// <param name="value">The color to negate.</param>
        /// <param name="result">When the method completes, contains the negated color.</param>
        public static void Negate( ref Color4 value, out Color4 result )
        {
            result.A = 1.0f - value.A;
            result.R = 1.0f - value.R;
            result.G = 1.0f - value.G;
            result.B = 1.0f - value.B;
        }

        /// <summary>
        /// Negates a color.
        /// </summary>
        /// <param name="value">The color to negate.</param>
        /// <returns>The negated color.</returns>
        public static Color4 Negate( Color4 value )
        {
            return new Color4( 1.0f - value.R, 1.0f - value.G, 1.0f - value.B, 1.0f - value.A );
        }

        /// <summary>
        /// Restricts a value to be within a specified range.
        /// </summary>
        /// <param name="value">The value to clamp.</param>
        /// <param name="min">The minimum value.</param>
        /// <param name="max">The maximum value.</param>
        /// <param name="result">When the method completes, contains the clamped value.</param>
        public static void Clamp( ref Color4 value, ref Color4 min, ref Color4 max, out Color4 result )
        {
            float alpha = value.A;
            alpha = ( alpha > max.A ) ? max.A : alpha;
            alpha = ( alpha < min.A ) ? min.A : alpha;

            float red = value.R;
            red = ( red > max.R ) ? max.R : red;
            red = ( red < min.R ) ? min.R : red;

            float green = value.G;
            green = ( green > max.G ) ? max.G : green;
            green = ( green < min.G ) ? min.G : green;

            float blue = value.B;
            blue = ( blue > max.B ) ? max.B : blue;
            blue = ( blue < min.B ) ? min.B : blue;

            result = new Color4( red, green, blue, alpha );
        }

        /// <summary>
        /// Restricts a value to be within a specified range.
        /// </summary>
        /// <param name="value">The value to clamp.</param>
        /// <param name="min">The minimum value.</param>
        /// <param name="max">The maximum value.</param>
        /// <returns>The clamped value.</returns>
        public static Color4 Clamp( Color4 value, Color4 min, Color4 max )
        {
            Color4 result;
            Clamp( ref value, ref min, ref max, out result );
            return result;
        }

        /// <summary>
        /// Performs a linear interpolation between two colors.
        /// </summary>
        /// <param name="start">Start color.</param>
        /// <param name="end">End color.</param>
        /// <param name="amount">Value between 0 and 1 indicating the weight of <paramref name="end"/>.</param>
        /// <param name="result">When the method completes, contains the linear interpolation of the two colors.</param>
        /// <remarks>
        /// Passing <paramref name="amount"/> a value of 0 will cause <paramref name="start"/> to be returned; a value of 1 will cause <paramref name="end"/> to be returned.
        /// </remarks>
        public static void Lerp( ref Color4 start, ref Color4 end, float amount, out Color4 result )
        {
            result.R = MathUtil.Lerp( start.R, end.R, amount );
            result.G = MathUtil.Lerp( start.G, end.G, amount );
            result.B = MathUtil.Lerp( start.B, end.B, amount );
            result.A = MathUtil.Lerp( start.A, end.A, amount );
        }

        /// <summary>
        /// Performs a linear interpolation between two colors.
        /// </summary>
        /// <param name="start">Start color.</param>
        /// <param name="end">End color.</param>
        /// <param name="amount">Value between 0 and 1 indicating the weight of <paramref name="end"/>.</param>
        /// <returns>The linear interpolation of the two colors.</returns>
        /// <remarks>
        /// Passing <paramref name="amount"/> a value of 0 will cause <paramref name="start"/> to be returned; a value of 1 will cause <paramref name="end"/> to be returned.
        /// </remarks>
        public static Color4 Lerp( Color4 start, Color4 end, float amount )
        {
            Color4 result;
            Lerp( ref start, ref end, amount, out result );
            return result;
        }

        /// <summary>
        /// Performs a cubic interpolation between two colors.
        /// </summary>
        /// <param name="start">Start color.</param>
        /// <param name="end">End color.</param>
        /// <param name="amount">Value between 0 and 1 indicating the weight of <paramref name="end"/>.</param>
        /// <param name="result">When the method completes, contains the cubic interpolation of the two colors.</param>
        public static void SmoothStep( ref Color4 start, ref Color4 end, float amount, out Color4 result )
        {
            amount = MathUtil.SmoothStep( amount );
            Lerp( ref start, ref end, amount, out result );
        }

        /// <summary>
        /// Performs a cubic interpolation between two colors.
        /// </summary>
        /// <param name="start">Start color.</param>
        /// <param name="end">End color.</param>
        /// <param name="amount">Value between 0 and 1 indicating the weight of <paramref name="end"/>.</param>
        /// <returns>The cubic interpolation of the two colors.</returns>
        public static Color4 SmoothStep( Color4 start, Color4 end, float amount )
        {
            Color4 result;
            SmoothStep( ref start, ref end, amount, out result );
            return result;
        }

        /// <summary>
        /// Returns a color containing the smallest components of the specified colors.
        /// </summary>
        /// <param name="left">The first source color.</param>
        /// <param name="right">The second source color.</param>
        /// <param name="result">When the method completes, contains an new color composed of the largest components of the source colors.</param>
        public static void Max( ref Color4 left, ref Color4 right, out Color4 result )
        {
            result.A = ( left.A > right.A ) ? left.A : right.A;
            result.R = ( left.R > right.R ) ? left.R : right.R;
            result.G = ( left.G > right.G ) ? left.G : right.G;
            result.B = ( left.B > right.B ) ? left.B : right.B;
        }

        /// <summary>
        /// Returns a color containing the largest components of the specified colors.
        /// </summary>
        /// <param name="left">The first source color.</param>
        /// <param name="right">The second source color.</param>
        /// <returns>A color containing the largest components of the source colors.</returns>
        public static Color4 Max( Color4 left, Color4 right )
        {
            Color4 result;
            Max( ref left, ref right, out result );
            return result;
        }

        /// <summary>
        /// Returns a color containing the smallest components of the specified colors.
        /// </summary>
        /// <param name="left">The first source color.</param>
        /// <param name="right">The second source color.</param>
        /// <param name="result">When the method completes, contains an new color composed of the smallest components of the source colors.</param>
        public static void Min( ref Color4 left, ref Color4 right, out Color4 result )
        {
            result.A = ( left.A < right.A ) ? left.A : right.A;
            result.R = ( left.R < right.R ) ? left.R : right.R;
            result.G = ( left.G < right.G ) ? left.G : right.G;
            result.B = ( left.B < right.B ) ? left.B : right.B;
        }

        /// <summary>
        /// Returns a color containing the smallest components of the specified colors.
        /// </summary>
        /// <param name="left">The first source color.</param>
        /// <param name="right">The second source color.</param>
        /// <returns>A color containing the smallest components of the source colors.</returns>
        public static Color4 Min( Color4 left, Color4 right )
        {
            Color4 result;
            Min( ref left, ref right, out result );
            return result;
        }

        /// <summary>
        /// Adjusts the contrast of a color.
        /// </summary>
        /// <param name="value">The color whose contrast is to be adjusted.</param>
        /// <param name="contrast">The amount by which to adjust the contrast.</param>
        /// <param name="result">When the method completes, contains the adjusted color.</param>
        public static void AdjustContrast( ref Color4 value, float contrast, out Color4 result )
        {
            result.A = value.A;
            result.R = 0.5f + contrast * ( value.R - 0.5f );
            result.G = 0.5f + contrast * ( value.G - 0.5f );
            result.B = 0.5f + contrast * ( value.B - 0.5f );
        }

        /// <summary>
        /// Adjusts the contrast of a color.
        /// </summary>
        /// <param name="value">The color whose contrast is to be adjusted.</param>
        /// <param name="contrast">The amount by which to adjust the contrast.</param>
        /// <returns>The adjusted color.</returns>
        public static Color4 AdjustContrast( Color4 value, float contrast )
        {
            return new Color4(
                0.5f + contrast * ( value.R - 0.5f ),
                0.5f + contrast * ( value.G - 0.5f ),
                0.5f + contrast * ( value.B - 0.5f ),
                value.A );
        }

        /// <summary>
        /// Adjusts the saturation of a color.
        /// </summary>
        /// <param name="value">The color whose saturation is to be adjusted.</param>
        /// <param name="saturation">The amount by which to adjust the saturation.</param>
        /// <param name="result">When the method completes, contains the adjusted color.</param>
        public static void AdjustSaturation( ref Color4 value, float saturation, out Color4 result )
        {
            float grey = value.R * 0.2125f + value.G * 0.7154f + value.B * 0.0721f;

            result.A = value.A;
            result.R = grey + saturation * ( value.R - grey );
            result.G = grey + saturation * ( value.G - grey );
            result.B = grey + saturation * ( value.B - grey );
        }

        /// <summary>
        /// Adjusts the saturation of a color.
        /// </summary>
        /// <param name="value">The color whose saturation is to be adjusted.</param>
        /// <param name="saturation">The amount by which to adjust the saturation.</param>
        /// <returns>The adjusted color.</returns>
        public static Color4 AdjustSaturation( Color4 value, float saturation )
        {
            float grey = value.R * 0.2125f + value.G * 0.7154f + value.B * 0.0721f;

            return new Color4(
                grey + saturation * ( value.R - grey ),
                grey + saturation * ( value.G - grey ),
                grey + saturation * ( value.B - grey ),
                value.A );
        }

        /// <summary>
        /// Premultiplies the color components by the alpha value.
        /// </summary>
        /// <param name="value">The color to premultiply.</param>
        /// <returns>A color with premultiplied alpha.</returns>
        public static Color4 PremultiplyAlpha( Color4 value )
        {
            return new Color4( value.R * value.A, value.G * value.A, value.B * value.A, value.A );
        }

        /// <summary>
        /// Adds two colors.
        /// </summary>
        /// <param name="left">The first color to add.</param>
        /// <param name="right">The second color to add.</param>
        /// <returns>The sum of the two colors.</returns>
        public static Color4 operator +( Color4 left, Color4 right )
        {
            return new Color4( left.R + right.R, left.G + right.G, left.B + right.B, left.A + right.A );
        }

        /// <summary>
        /// Assert a color (return it unchanged).
        /// </summary>
        /// <param name="value">The color to assert (unchanged).</param>
        /// <returns>The asserted (unchanged) color.</returns>
        public static Color4 operator +( Color4 value )
        {
            return value;
        }

        /// <summary>
        /// Subtracts two colors.
        /// </summary>
        /// <param name="left">The first color to subtract.</param>
        /// <param name="right">The second color to subtract.</param>
        /// <returns>The difference of the two colors.</returns>
        public static Color4 operator -( Color4 left, Color4 right )
        {
            return new Color4( left.R - right.R, left.G - right.G, left.B - right.B, left.A - right.A );
        }

        /// <summary>
        /// Negates a color.
        /// </summary>
        /// <param name="value">The color to negate.</param>
        /// <returns>A negated color.</returns>
        public static Color4 operator -( Color4 value )
        {
            return new Color4( -value.R, -value.G, -value.B, -value.A );
        }

        /// <summary>
        /// Scales a color.
        /// </summary>
        /// <param name="scale">The factor by which to scale the color.</param>
        /// <param name="value">The color to scale.</param>
        /// <returns>The scaled color.</returns>
        public static Color4 operator *( float scale, Color4 value )
        {
            return new Color4( value.R * scale, value.G * scale, value.B * scale, value.A * scale );
        }

        /// <summary>
        /// Scales a color.
        /// </summary>
        /// <param name="value">The factor by which to scale the color.</param>
        /// <param name="scale">The color to scale.</param>
        /// <returns>The scaled color.</returns>
        public static Color4 operator *( Color4 value, float scale )
        {
            return new Color4( value.R * scale, value.G * scale, value.B * scale, value.A * scale );
        }

        /// <summary>
        /// Modulates two colors.
        /// </summary>
        /// <param name="left">The first color to modulate.</param>
        /// <param name="right">The second color to modulate.</param>
        /// <returns>The modulated color.</returns>
        public static Color4 operator *( Color4 left, Color4 right )
        {
            return new Color4( left.R * right.R, left.G * right.G, left.B * right.B, left.A * right.A );
        }

        /// <summary>
        /// Tests for equality between two objects.
        /// </summary>
        /// <param name="left">The first value to compare.</param>
        /// <param name="right">The second value to compare.</param>
        /// <returns><c>true</c> if <paramref name="left"/> has the same value as <paramref name="right"/>; otherwise, <c>false</c>.</returns>
        public static bool operator ==( Color4 left, Color4 right )
        {
            return left.Equals( right );
        }

        /// <summary>
        /// Tests for inequality between two objects.
        /// </summary>
        /// <param name="left">The first value to compare.</param>
        /// <param name="right">The second value to compare.</param>
        /// <returns><c>true</c> if <paramref name="left"/> has a different value than <paramref name="right"/>; otherwise, <c>false</c>.</returns>
        public static bool operator !=( Color4 left, Color4 right )
        {
            return !left.Equals( right );
        }

        /// <summary>
        /// Performs an explicit conversion from <see cref="Color4"/> to <see cref="Color3"/>.
        /// </summary>
        /// <param name="value">The value.</param>
        /// <returns>The result of the conversion.</returns>
        public static explicit operator Color3( Color4 value )
        {
            return new Color3( value.R, value.G, value.B );
        }

        /// <summary>
        /// Performs an explicit conversion from <see cref="Color4"/> to <see cref="Vec3"/>.
        /// </summary>
        /// <param name="value">The value.</param>
        /// <returns>The result of the conversion.</returns>
        public static explicit operator Vec3( Color4 value )
        {
            return new Vec3( value.R, value.G, value.B );
        }

        /// <summary>
        /// Performs an implicit conversion from <see cref="Color4"/> to <see cref="Vec4"/>.
        /// </summary>
        /// <param name="value">The value.</param>
        /// <returns>The result of the conversion.</returns>
        public static implicit operator Vec4( Color4 value )
        {
            return new Vec4( value.R, value.G, value.B, value.A );
        }

        /// <summary>
        /// Performs an explicit conversion from <see cref="Vec3"/> to <see cref="Color4"/>.
        /// </summary>
        /// <param name="value">The value.</param>
        /// <returns>The result of the conversion.</returns>
        public static explicit operator Color4( Vec3 value )
        {
            return new Color4( value.X, value.Y, value.Z, 1.0f );
        }

        /// <summary>
        /// Performs an explicit conversion from <see cref="Vec4"/> to <see cref="Color4"/>.
        /// </summary>
        /// <param name="value">The value.</param>
        /// <returns>The result of the conversion.</returns>
        public static explicit operator Color4( Vec4 value )
        {
            return new Color4( value.X, value.Y, value.Z, value.W );
        }

        /// <summary>
        /// Performs an explicit conversion from <see cref="Vec3"/> to <see cref="Color4"/>.
        /// </summary>
        /// <param name="value">The value.</param>
        /// <returns>The result of the conversion.</returns>
        public static explicit operator Color4( ColorBGRA value )
        {
            return new Color4( value );
        }

        /// <summary>
        /// Performs an explicit conversion from <see cref="Vec4"/> to <see cref="Color4"/>.
        /// </summary>
        /// <param name="value">The value.</param>
        /// <returns>The result of the conversion.</returns>
        public static explicit operator ColorBGRA( Color4 value )
        {
            return new ColorBGRA( value.R, value.G, value.B, value.A );
        }

        /// <summary>
        /// Performs an explicit conversion from <see cref="Color4"/> to <see cref="int"/>.
        /// </summary>
        /// <param name="value">The value.</param>
        /// <returns>
        /// The result of the conversion.
        /// </returns>
        public static explicit operator int( Color4 value )
        {
            return value.ToRgba();
        }

        /// <summary>
        /// Performs an explicit conversion from <see cref="int"/> to <see cref="Color4"/>.
        /// </summary>
        /// <param name="value">The value.</param>
        /// <returns>
        /// The result of the conversion.
        /// </returns>
        public static explicit operator Color4( int value )
        {
            return new Color4( value );
        }

        /// <summary>
        /// Converts this color to an equivalent <see cref="Color3"/>, discarding the alpha channel.
        /// </summary>
        /// <returns>An equivalent <see cref="Color3"/>, discarding the alpha channel.</returns>
        public Color3 ToColor3()
        {
            return new Color3( R, G, B );
        }

        /// <summary>
        /// Returns a <see cref="string"/> that represents this instance.
        /// </summary>
        /// <returns>
        /// A <see cref="string"/> that represents this instance.
        /// </returns>
        public override string ToString()
        {
            return ToString( CultureInfo.CurrentCulture );
        }

        /// <summary>
        /// Returns a <see cref="string"/> that represents this instance.
        /// </summary>
        /// <param name="format">The format to apply to each channel (float).</param>
        /// <returns>
        /// A <see cref="string"/> that represents this instance.
        /// </returns>
        public string ToString( string format )
        {
            return ToString( format, CultureInfo.CurrentCulture );
        }

        /// <summary>
        /// Returns a <see cref="string"/> that represents this instance.
        /// </summary>
        /// <param name="formatProvider">The format provider.</param>
        /// <returns>
        /// A <see cref="string"/> that represents this instance.
        /// </returns>
        public string ToString( IFormatProvider formatProvider )
        {
            return string.Format( formatProvider, ToStringFormat, A, R, G, B );
        }

        /// <summary>
        /// Returns a <see cref="string"/> that represents this instance.
        /// </summary>
        /// <param name="format">The format to apply to each channel (float).</param>
        /// <param name="formatProvider">The format provider.</param>
        /// <returns>
        /// A <see cref="string"/> that represents this instance.
        /// </returns>
        public string ToString( string format, IFormatProvider formatProvider )
        {
            if( format == null )
                return ToString( formatProvider );

            return string.Format( formatProvider, ToStringFormat,
                                 A.ToString( format, formatProvider ),
                                 R.ToString( format, formatProvider ),
                                 G.ToString( format, formatProvider ),
                                 B.ToString( format, formatProvider ) );
        }

        /// <summary>
        /// Returns a hash code for this instance.
        /// </summary>
        /// <returns>
        /// A hash code for this instance, suitable for use in hashing algorithms and data structures like a hash table.
        /// </returns>
        public override int GetHashCode()
        {
            return A.GetHashCode() + R.GetHashCode() + G.GetHashCode() + B.GetHashCode();
        }

        /// <summary>
        /// Determines whether the specified <see cref="Color4"/> is equal to this instance.
        /// </summary>
        /// <param name="other">The <see cref="Color4"/> to compare with this instance.</param>
        /// <returns>
        /// <c>true</c> if the specified <see cref="Color4"/> is equal to this instance; otherwise, <c>false</c>.
        /// </returns>
        public bool Equals( Color4 other )
        {
            return A == other.A && R == other.R && G == other.G && B == other.B;
        }

        /// <summary>
        /// Determines whether the specified <see cref="object"/> is equal to this instance.
        /// </summary>
        /// <param name="value">The <see cref="object"/> to compare with this instance.</param>
        /// <returns>
        /// <c>true</c> if the specified <see cref="object"/> is equal to this instance; otherwise, <c>false</c>.
        /// </returns>
        public override bool Equals( object value )
        {
            if( value == null )
                return false;

            if( !ReferenceEquals( value.GetType(), typeof( Color4 ) ) )
                return false;

            return Equals( (Color4)value );
        }
    }
}