ImageSharp/src/ImageProcessor/Processors/Constrain.cs

// --------------------------------------------------------------------------------------------------------------------
// <copyright file="Constrain.cs" company="James South">
//   Copyright (c) James South.
//   Licensed under the Apache License, Version 2.0.
// </copyright>
// <summary>
//   Constrains an image to the given dimensions.
// </summary>
// --------------------------------------------------------------------------------------------------------------------

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

    /// <summary>
    /// Constrains an image to the given dimensions.
    /// </summary>
    public class Constrain : ResizeBase
    {
        /// <summary>
        /// The regular expression to search strings for.
        /// </summary>
        private static readonly Regex QueryRegex = new Regex(@"constrain=\d+[,-]\d+", RegexOptions.Compiled);

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

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

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

        /// <summary>
        /// Gets or sets any additional settings required by the processor.
        /// </summary>
        public override 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 override 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[] constraints = match.Value.ToPositiveIntegerArray();

                        int x = constraints[0];
                        int y = constraints[1];

                        this.DynamicParameter = new Size(x, y);
                    }

                    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 override Image ProcessImage(ImageFactory factory)
        {
            double constrainedWidth = this.DynamicParameter.Width;
            double constrainedHeight = this.DynamicParameter.Height;

            Image original = factory.Image;
            double width = original.Width;
            double height = original.Height;

            if (width > constrainedWidth || height > constrainedHeight)
            {
                double constraintRatio = constrainedHeight / constrainedWidth;
                double originalRatio = height / width;

                Size newSize = originalRatio < constraintRatio
                                   ? new Size((int)constrainedWidth, 0)
                                   : new Size(0, (int)constrainedHeight);

                int defaultMaxWidth;
                int defaultMaxHeight;
                int.TryParse(this.Settings["MaxWidth"], out defaultMaxWidth);
                int.TryParse(this.Settings["MaxHeight"], out defaultMaxHeight);

                return this.ResizeImage(factory, newSize.Width, newSize.Height, defaultMaxWidth, defaultMaxHeight, Color.Transparent);
            }

            return factory.Image;
        }
        #endregion
    }
}