ResizeType.cs

using System;
using System.Collections.Generic;
using System.Drawing;
using System.Text;

namespace lcorneliussen
{
    public interface IResizeType
    {
        Size CalcNewSize(Size currentSize, Size newSize, bool resizeIfSmaller);
    }

    /// <summary>
    /// Offers some helpful methods for image resizing.
    /// </summary>
    public class ResizeType
    {
        /// <summary>
        /// Returns the new size by fixed height.
        /// </summary>
        public static IResizeType FixedHeight = new FixedHeightResizeType();

        /// <summary>
        /// Returns the new size by fixed width.
        /// </summary>
        public static IResizeType FixedWidth = new FixedWidthResizeType();

        /// <summary>
        /// Returns a size wich fits in a target size.
        /// </summary>
        public static IResizeType Fit = new FitResizeType();

        /// <summary>
        /// Stretches a image to the given size.
        /// </summary>
        public static IResizeType Stretched = new StretchedResizeType();

        private static int CalcNewHeight(int currentWidth, int currentHeight, int newWidth)
        {
            float ratio = (float)newWidth / (float)currentWidth;
            float newHeight = currentHeight * ratio;

            return (int)newHeight;
        }

        private static int CalcNewWidth(int currentWidth, int currentHeight, int newHeight)
        {
            float ratio = (float)newHeight / (float)currentHeight;
            float newWidth = currentWidth * ratio;

            return (int)newWidth;
        }

        private class FixedHeightResizeType : IResizeType
        {
            public Size CalcNewSize(Size currentSize, Size newSize, bool resizeIfSmaller)
            {
                int height = newSize.Height;

                if (!resizeIfSmaller)
                {
                    if (height > currentSize.Height) height = currentSize.Height;
                }

                int newWidth = CalcNewWidth(currentSize.Width, currentSize.Height, height);
                return new Size(newWidth, height);
            }
        }

        private class FixedWidthResizeType : IResizeType
        {
            public Size CalcNewSize(Size currentSize, Size newSize, bool resizeIfSmaller)
            {
                int width = newSize.Width;
                
                if (!resizeIfSmaller)
                {
                    if (width > currentSize.Width) width = currentSize.Width;
                }

                int newHeight = CalcNewHeight(currentSize.Width, currentSize.Height, width);
                return new Size(width, newHeight);
            }
        }

        private class FitResizeType : IResizeType
        {
            public Size CalcNewSize(Size currentSize, Size newSize, bool resizeIfSmaller)
            {
                int width = newSize.Width;
                int height = newSize.Height;

                int newWidth = currentSize.Width;
                int newHeight = currentSize.Height;

                if (!resizeIfSmaller) // break, if newSize allready fits in currentSize
                    if (currentSize.Height < height && currentSize.Width < width)
                        return new Size(currentSize.Width, currentSize.Height);

                if(width != newWidth) // shrink or expand to width
                {
                    newHeight = CalcNewHeight(currentSize.Width, currentSize.Height, width);
                    newWidth = width;
                }
                if (newHeight > height) //shrink to fit height, if neccesarry
                {
                    newWidth = CalcNewWidth(newWidth, newHeight, height);
                    newHeight = height;
                }

                return new Size(newWidth, newHeight);
            }
        }

        private class StretchedResizeType : IResizeType
        {
            public Size CalcNewSize(Size currentSize, Size newSize, bool resizeIfSmaller)
            {
                int w = newSize.Width;
                int h = newSize.Height;

                if (!resizeIfSmaller)
                {
                    if (w > currentSize.Width) w = currentSize.Width;
                    if (h > currentSize.Height) h = currentSize.Height;
                }

                return new Size(w, h);
            }
        }
    }
}