ImageSharp/src/ImageProcessor/Processors/Alpha.cs

// --------------------------------------------------------------------------------------------------------------------
// <copyright file="Alpha.cs" company="James South">
//   Copyright (c) James South.
//   Licensed under the Apache License, Version 2.0.
// </copyright>
// <summary>
//   Encapsulates methods to change the alpha component of the image to effect its transparency.
// </summary>
// --------------------------------------------------------------------------------------------------------------------

namespace ImageProcessor.Processors
{
    #region Using
    using System.Collections.Generic;
    using System.Drawing;
    using System.Drawing.Imaging;
    using System.Text.RegularExpressions;
    #endregion

    /// <summary>
    /// Encapsulates methods to change the alpha component of the image to effect its transparency.
    /// </summary>
    public class Alpha : IGraphicsProcessor
    {
        /// <summary>
        /// The regular expression to search strings for.
        /// <see cref="http://stackoverflow.com/a/6400969/427899"/> 
        /// </summary>
        private static readonly Regex QueryRegex = new Regex(@"alpha=(?:100|[1-9]?[0-9])", RegexOptions.Compiled);

        #region IGraphicsProcessor Members
        /// <summary>
        /// Gets the regular expression to search strings for.
        /// </summary>
        public Regex RegexPattern
        {
            get
            {
                return QueryRegex;
            }
        }

        /// <summary>
        /// Gets or sets DynamicParameter.
        /// </summary>
        public dynamic DynamicParameter
        {
            get;
            set;
        }

        /// <summary>
        /// Gets the order in which this processor is to be used in a chain.
        /// </summary>
        public int SortOrder
        {
            get;
            private set;
        }

        /// <summary>
        /// Gets or sets any additional settings required by the processor.
        /// </summary>
        public Dictionary<string, string> Settings
        {
            get;
            set;
        }

        /// <summary>
        /// The position in the original string where the first character of the captured substring was found.
        /// </summary>
        /// <param name="queryString">
        /// The query string to search.
        /// </param>
        /// <returns>
        /// The zero-based starting position in the original string where the captured substring was found.
        /// </returns>
        public int MatchRegexIndex(string queryString)
        {
            int index = 0;

            // Set the sort order to max to allow filtering.
            this.SortOrder = int.MaxValue;

            foreach (Match match in this.RegexPattern.Matches(queryString))
            {
                if (match.Success)
                {
                    if (index == 0)
                    {
                        // Set the index on the first instance only.
                        this.SortOrder = match.Index;
                        int percentage = int.Parse(match.Value.Split('=')[1]);

                        this.DynamicParameter = percentage;
                    }

                    index += 1;
                }
            }

            return this.SortOrder;
        }

        /// <summary>
        /// Processes the image.
        /// </summary>
        /// <param name="factory">
        /// The the current instance of the <see cref="T:ImageProcessor.ImageFactory"/> class containing
        /// the image to process.
        /// </param>
        /// <returns>
        /// The processed image from the current instance of the <see cref="T:ImageProcessor.ImageFactory"/> class.
        /// </returns>
        public Image ProcessImage(ImageFactory factory)
        {
            Bitmap newImage = null;
            Image image = factory.Image;

            try
            {
                int alphaPercent = this.DynamicParameter;

                // Don't use an object initializer here.
                // ReSharper disable once UseObjectOrCollectionInitializer
                newImage = new Bitmap(image.Width, image.Height, PixelFormat.Format32bppPArgb);
                newImage.Tag = image.Tag;

                ColorMatrix colorMatrix = new ColorMatrix();
                colorMatrix.Matrix00 = colorMatrix.Matrix11 = colorMatrix.Matrix22 = colorMatrix.Matrix44 = 1;
                colorMatrix.Matrix33 = (float)alphaPercent / 100;

                using (Graphics graphics = Graphics.FromImage(newImage))
                {
                    using (ImageAttributes imageAttributes = new ImageAttributes())
                    {
                        imageAttributes.SetColorMatrix(colorMatrix);

                        graphics.DrawImage(image, new Rectangle(0, 0, image.Width, image.Height), 0, 0, image.Width, image.Height, GraphicsUnit.Pixel, imageAttributes);

                        image.Dispose();
                        image = newImage;
                    }
                }
            }
            catch
            {
                if (newImage != null)
                {
                    newImage.Dispose();
                }
            }

            return image;
        }
        #endregion
    }
}