照片生成缩略图时的尺寸计算

为了能保持住照片在缩小时不变形,所以需要重新计算缩略图的尺寸. 这里默认缩略图的尺寸的应该满足 长 >= 宽, 否则计算规则应有所变化.

今天突然想明白了，记在这里以后备用.

        /// <summary>
        /// 取得缩略图的尺寸
        /// </summary>
        /// <param name="oldSize">原始尺寸</param>
        /// <param name="desiredSize">目标尺寸</param>
        /// <returns></returns>
        public static Size GetSacaledSize(Size oldSize, Size desiredSize)
        {
            if (oldSize.Height == 0 || oldSize.Width == 0)
                throw new Exception("The pic's width and height not set.");

            Size outSize = new Size();
            bool flag = false;

            //如果宽> 长,则按宽缩放 width = DesiredWidth.
            //如果 宽<= 长. 则按长缩放 height = DesiredHeight.

            if (oldSize.Width <= desiredSize.Width && oldSize.Height <= desiredSize.Height)
            {
                outSize = oldSize;
                flag = true;
            }

            if (!flag)
            {
                if (oldSize.Width > oldSize.Height)
                {
                    outSize.Width = desiredSize.Width;
                    double ratio = (double)desiredSize.Width / oldSize.Width;
                    outSize.Height = Convert.ToInt32(oldSize.Height * ratio);
                    flag = true;
                }
            }

            if (!flag)
            {
                outSize.Height = desiredSize.Height;
                double ratio = (double)desiredSize.Height / oldSize.Height;
                outSize.Width = Convert.ToInt32(oldSize.Width * ratio);
            }


            return outSize;
        }

这里是单元测试代码:

    /// <summary>
    /// 这个测试用来测试在几种不同尺寸下面的缩略图尺寸算法的问题.
    /// </summary>
    [TestFixture]
    public class PhotoCacheTestFixture
    {
        [Test]
        public void CacheSizeTest()
        {
            Photos p = new Photos();

            //常见情况, 长大于宽的尺寸.
            p.PhotoHeight = 1200;
            p.PhotoWidth = 1600;

            Size sizeSacled = p.SacledSize(ScaledPicSize.Instance.Size130x130);

            Console.WriteLine("1600X1200");
            Console.WriteLine(sizeSacled.Width);
            Console.WriteLine(sizeSacled.Height);
            Console.WriteLine("++++++++++++++++++");
            
            Assert.IsTrue(sizeSacled.Width <= 130);
            Assert.IsTrue(sizeSacled.Height <= 130);

            //原图比缩略图尺寸还小的情况.直接返回原尺寸.
            p.PhotoWidth = 100;
            p.PhotoHeight = 80;

            Size size2 = p.SacledSize(ScaledPicSize.Instance.Size130x130);

            Console.WriteLine("100X80");
            Console.WriteLine(size2.Width);
            Console.WriteLine(size2.Height);
            Console.WriteLine("++++++++++++++++++");


            Assert.IsTrue(size2.Width <= 130);
            Assert.IsTrue(size2.Height <= 130);

            // 长版的图片尺寸.

            p.PhotoWidth = 80;
            p.PhotoHeight = 140;

            Size size3 = p.SacledSize(ScaledPicSize.Instance.Size130x130);

            Console.WriteLine("80X140");
            Console.WriteLine(size3.Width);
            Console.WriteLine(size3.Height);
            Console.WriteLine("++++++++++++++++++");

            Assert.IsTrue(size3.Width <= 130);
            Assert.IsTrue(size3.Height <= 130);
        }
    }