DrawingUtility 增加处理图像旋转的方法，增加等比例缩放的方法。

Apewer/DrawingUtility.cs

@@ -25,6 +25,72 @@ namespace Apewer
             return graphics;
         }
 
+        /// <summary>识别图像的旋转角度并进行调整。</summary>
+        /// <exception cref="ArgumentNullException"></exception>
+        public static void AdjustRotation(this Image image)
+        {
+            if (image == null) throw new ArgumentNullException(nameof(image));
+
+            // 检测旋转角度
+            var angle = 0;
+            if (Array.IndexOf(image.PropertyIdList, 274) > -1)
+            {
+                var property = image.GetPropertyItem(274);
+                var value = property.Value[0];
+                switch (value)
+                {
+                    case 1: break;
+                    case 3: angle = 180; break;
+                    case 6: angle = 90; break;
+                    case 8: angle = 270; break;
+                }
+            }
+
+            // 自适应旋转
+            switch (angle)
+            {
+                case 90: image.RotateFlip(RotateFlipType.Rotate90FlipNone); break;
+                case 180: image.RotateFlip(RotateFlipType.Rotate180FlipNone); break;
+                case 270: image.RotateFlip(RotateFlipType.Rotate270FlipNone); break;
+            }
+        }
+
+        /// <summary>作为图像，执行回调。</summary>
+        /// <exception cref="ArgumentNullException"></exception>
+        /// <exception cref="ArgumentException"></exception>
+        public static void AsImage(this byte[] imageData, Action<Image> callback)
+        {
+            if (imageData == null) throw new ArgumentNullException(nameof(imageData));
+            if (callback == null) throw new ArgumentNullException(nameof(callback));
+
+            using (var stream = new MemoryStream(imageData))
+            {
+                using (var image = Image.FromStream(stream))
+                {
+                    AdjustRotation(image);
+                    callback.Invoke(image);
+                }
+            }
+        }
+
+        /// <summary>作为图像，执行回调。</summary>
+        /// <exception cref="ArgumentNullException"></exception>
+        /// <exception cref="ArgumentException"></exception>
+        public static TResult AsImage<TResult>(this byte[] imageData, Func<Image, TResult> callback)
+        {
+            if (imageData == null) throw new ArgumentNullException(nameof(imageData));
+            if (callback == null) throw new ArgumentNullException(nameof(callback));
+
+            using (var stream = new MemoryStream(imageData))
+            {
+                using (var image = Image.FromStream(stream))
+                {
+                    AdjustRotation(image);
+                    return callback.Invoke(image);
+                }
+            }
+        }
+
         /// <summary>保存图像为文件。</summary>
         /// <exception cref="ArgumentNullException"></exception>
         public static byte[] Save(this Image image, ImageFormat format)
@@ -63,6 +129,38 @@ namespace Apewer
             }
         }
 
+        /// <summary>等比例缩放，生成新图像。</summary>
+        /// <exception cref="ArgumentNullException"></exception>
+        /// <exception cref="ArgumentOutOfRangeException"></exception>
+        public static Image AspectScale(this Image origin, int maxSide, Color? backgroundColor = null) => AspectScale(origin, maxSide, maxSide, backgroundColor);
+
+        /// <summary>等比例缩放，生成新图像。</summary>
+        /// <exception cref="ArgumentNullException"></exception>
+        /// <exception cref="ArgumentOutOfRangeException"></exception>
+        public static Image AspectScale(this Image origin, int maxWidth, int maxHeight, Color? backgroundColor = null)
+        {
+            if (origin == null) throw new ArgumentNullException(nameof(origin));
+            if (maxWidth < 1) throw new ArgumentOutOfRangeException(nameof(maxWidth));
+            if (maxHeight < 1) throw new ArgumentOutOfRangeException(nameof(maxHeight));
+
+            var width = origin.Width;
+            var height = origin.Height;
+
+            var radio = Convert.ToDouble(width) / Convert.ToDouble(height);
+            if (width > maxWidth)
+            {
+                width = maxWidth;
+                height = Convert.ToInt32(maxWidth / radio);
+            }
+            if (height > maxHeight)
+            {
+                width = Convert.ToInt32(maxHeight * radio);
+                height = maxHeight;
+            }
+
+            return Scale(origin, width, height, backgroundColor);
+        }
+
         /// <summary>缩放图像，生成新图像。</summary>
         /// <param name="image">原始图像。</param>
         /// <param name="size">新图像的大小。</param>
@@ -102,6 +200,7 @@ namespace Apewer
                     if (isTransparentFormat)
                     {
                         if (backgroundColor != null && backgroundColor.HasValue) graphic.Clear(backgroundColor.Value);
+                        else graphic.Clear(Color.Transparent);
                     }
 
                     // 绘制新图像