SvgColourConverter.cs

using System;
using System.Collections.Generic;
using System.Drawing;
using System.Globalization;
using System.Linq;
using System.Text;
using System.Threading;

namespace Svg
{
    /// <summary>
    /// Converts string representations of colours into <see cref="Color"/> objects.
    /// </summary>
    public class SvgColourConverter : System.Drawing.ColorConverter
    {
        /// <summary>
        /// Converts the given object to the converter's native type.
        /// </summary>
        /// <param name="context">A <see cref="T:System.ComponentModel.TypeDescriptor"/> that provides a format context. You can use this object to get additional information about the environment from which this converter is being invoked.</param>
        /// <param name="culture">A <see cref="T:System.Globalization.CultureInfo"/> that specifies the culture to represent the color.</param>
        /// <param name="value">The object to convert.</param>
        /// <returns>
        /// An <see cref="T:System.Object"/> representing the converted value.
        /// </returns>
        /// <exception cref="T:System.ArgumentException">The conversion cannot be performed.</exception>
        /// <PermissionSet>
        /// 	<IPermission class="System.Security.Permissions.FileIOPermission, mscorlib, Version=2.0.3600.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" version="1" Unrestricted="true"/>
        /// </PermissionSet>
        public override object ConvertFrom(System.ComponentModel.ITypeDescriptorContext context, System.Globalization.CultureInfo culture, object value)
        {
            string colour = value as string;

            if (colour != null)
            {
                var oldCulture = Thread.CurrentThread.CurrentCulture;
                Thread.CurrentThread.CurrentCulture = System.Globalization.CultureInfo.InvariantCulture;
                
                colour = colour.Trim();

                if (colour.StartsWith("rgb"))
                {
                    try
                    {
                        int start = colour.IndexOf("(") + 1;
                        
                        //get the values from the RGB string
                        string[] values = colour.Substring(start, colour.IndexOf(")") - start).Split(new char[]{',', ' '}, StringSplitOptions.RemoveEmptyEntries);

                        //determine the alpha value if this is an RGBA (it will be the 4th value if there is one)
                        int alphaValue = 255;
                        if (values.Length > 3)
                        {
                            //the alpha portion of the rgba is not an int 0-255 it is a decimal between 0 and 1
                            //so we have to determine the corosponding byte value
                            var alphastring = values[3];
                            if(alphastring.StartsWith("."))
                            {
                                alphastring = "0" + alphastring;
                            }

                            var alphaDecimal = decimal.Parse(alphastring);

                            if(alphaDecimal <= 1)
                            {
                                alphaValue = (int)(alphaDecimal * 255);
                            }
                            else
                            {
                                alphaValue = (int)alphaDecimal;
                            }
                        }

                        Color colorpart;
                        if (values[0].Trim().EndsWith("%"))
                        {
                            colorpart = System.Drawing.Color.FromArgb(alphaValue, (int)(255 * float.Parse(values[0].Trim().TrimEnd('%')) / 100f),
                                                                                  (int)(255 * float.Parse(values[1].Trim().TrimEnd('%')) / 100f),
                                                                                  (int)(255 * float.Parse(values[2].Trim().TrimEnd('%')) / 100f));
                        }
                        else
                        {
                            colorpart = System.Drawing.Color.FromArgb(alphaValue, int.Parse(values[0]), int.Parse(values[1]), int.Parse(values[2]));
                        }

                        return colorpart;
                    }
                    catch
                    {
                        throw new SvgException("Colour is in an invalid format: '" + colour + "'");
                    }
                }
                // HSL support
                else if ( colour.StartsWith( "hsl" ) ) {
                    try
                    {
                        int start = colour.IndexOf("(") + 1;
                        
                        //get the values from the RGB string
                        string[] values = colour.Substring(start, colour.IndexOf(")") - start).Split(new char[]{',', ' '}, StringSplitOptions.RemoveEmptyEntries);
                        if ( values[1].EndsWith( "%" ) )
                        {
                            values[1] = values[1].TrimEnd( '%' );
                        }
                        if ( values[2].EndsWith( "%" ) ) 
                        {
                            values[2] = values[2].TrimEnd( '%' );
                        }
                        // Get the HSL values in a range from 0 to 1.
                        double h = double.Parse( values[0] ) / 360.0;
                        double s = double.Parse( values[1] ) / 100.0;
                        double l = double.Parse( values[2] ) / 100.0;
                        // Convert the HSL color to an RGB color
                        Color colorpart = Hsl2Rgb( h, s, l );
                        return colorpart;                    
                    }
                    catch
                    {
                        throw new SvgException("Colour is in an invalid format: '" + colour + "'");
                    }
                }
                else if (colour.StartsWith("#") && colour.Length == 4)
                {
                    colour = string.Format(culture, "#{0}{0}{1}{1}{2}{2}", colour[1], colour[2], colour[3]);
                    return base.ConvertFrom(context, culture, colour);
                }
                
                switch (colour.ToLowerInvariant())
                {
                    case "activeborder": return SystemColors.ActiveBorder;
                    case "activecaption": return SystemColors.ActiveCaption;
                    case "appworkspace": return SystemColors.AppWorkspace;
                    case "background": return SystemColors.Desktop;
                    case "buttonface": return SystemColors.Control;
                    case "buttonhighlight": return SystemColors.ControlLightLight;
                    case "buttonshadow": return SystemColors.ControlDark;
                    case "buttontext": return SystemColors.ControlText;
                    case "captiontext": return SystemColors.ActiveCaptionText;
                    case "graytext": return SystemColors.GrayText;
                    case "highlight": return SystemColors.Highlight;
                    case "highlighttext": return SystemColors.HighlightText;
                    case "inactiveborder": return SystemColors.InactiveBorder;
                    case "inactivecaption": return SystemColors.InactiveCaption;
                    case "inactivecaptiontext": return SystemColors.InactiveCaptionText;
                    case "infobackground": return SystemColors.Info;
                    case "infotext": return SystemColors.InfoText;
                    case "menu": return SystemColors.Menu;
                    case "menutext": return SystemColors.MenuText;
                    case "scrollbar": return SystemColors.ScrollBar;
                    case "threeddarkshadow": return SystemColors.ControlDarkDark;
                    case "threedface": return SystemColors.Control;
                    case "threedhighlight": return SystemColors.ControlLight;
                    case "threedlightshadow": return SystemColors.ControlLightLight;
                    case "window": return SystemColors.Window;
                    case "windowframe": return SystemColors.WindowFrame;
                    case "windowtext": return SystemColors.WindowText;
                }

                Thread.CurrentThread.CurrentCulture = oldCulture;
            }

            return base.ConvertFrom(context, culture, value);
        }

        public override bool CanConvertFrom(System.ComponentModel.ITypeDescriptorContext context, Type sourceType)
        {
            if (sourceType == typeof(string))
            {
                return true;
            }

            return base.CanConvertFrom(context, sourceType);
        }

        public override bool CanConvertTo(System.ComponentModel.ITypeDescriptorContext context, Type destinationType)
        {
            if (destinationType == typeof(string))
            {
                return true;
            }

            return base.CanConvertTo(context, destinationType);
        }

        public override object ConvertTo(System.ComponentModel.ITypeDescriptorContext context, System.Globalization.CultureInfo culture, object value, Type destinationType)
        {
            if (destinationType == typeof(string))
            {
                var colour = (Color)value;
                return "#" + colour.R.ToString("X2", null) + colour.G.ToString("X2", null) + colour.B.ToString("X2", null);
            }

            return base.ConvertTo(context, culture, value, destinationType);
        }

        /// <summary>
        /// Converts HSL color (with HSL specified from 0 to 1) to RGB color.
        /// Taken from http://www.geekymonkey.com/Programming/CSharp/RGB2HSL_HSL2RGB.htm
        /// </summary>
        /// <param name="h"></param>
        /// <param name="sl"></param>
        /// <param name="l"></param>
        /// <returns></returns>
        private static Color Hsl2Rgb( double h, double sl, double l ) {
            double r = l;   // default to gray
            double g = l;
            double b = l;
            double v = (l <= 0.5) ? (l * (1.0 + sl)) : (l + sl - l * sl);
            if (v > 0)
            {
                  double m;
                  double sv;
                  int sextant;
                  double fract, vsf, mid1, mid2;
 
                  m = l + l - v;
                  sv = (v - m ) / v;
                  h *= 6.0;
                  sextant = (int)h;
                  fract = h - sextant;
                  vsf = v * sv * fract;
                  mid1 = m + vsf;
                  mid2 = v - vsf;
                  switch (sextant)
                  {
                        case 0:
                              r = v;
                              g = mid1;
                              b = m;
                              break;
                        case 1:
                              r = mid2;
                              g = v;
                              b = m;
                              break;
                        case 2:
                              r = m;
                              g = v;
                              b = mid1;
                              break;
                        case 3:
                              r = m;
                              g = mid2;
                              b = v;
                              break;
                        case 4:
                              r = mid1;
                              g = m;
                              b = v;
                              break;
                        case 5:
                              r = v;
                              g = m;
                              b = mid2;
                              break;
                  }
            }
            Color rgb = Color.FromArgb( (int)( r * 255.0 ), (int)( g * 255.0 ), (int)( b * 255.0f ) );
            return rgb;        
        }

    }
}