keep image alpha in clipboard

FModel/Extensions/ClipboardExtensions.cs

@@ -0,0 +1,131 @@
+using SkiaSharp;
+
+using System;
+using System.Drawing;
+using System.IO;
+using System.Text;
+using System.Windows;
+
+namespace FModel.Extensions
+{
+    public static class ClipboardExtensions
+    {
+        public static void SetClipboardImage(byte[] pngBytes, string fileName = null)
+        {
+            Clipboard.Clear();
+            var data = new DataObject();
+            using var pngMs = new MemoryStream(pngBytes);
+            using var image = Image.FromStream(pngMs);
+            // As standard bitmap, without transparency support
+            data.SetData(DataFormats.Bitmap, image, true);
+            // As PNG. Gimp will prefer this over the other two
+            data.SetData("PNG", pngMs, false);
+            // As DIB. This is (wrongly) accepted as ARGB by many applications
+            using var dibMemStream = new MemoryStream(ConvertToDib(pngBytes));
+            data.SetData(DataFormats.Dib, dibMemStream, false);
+            // Optional fileName
+            if (!string.IsNullOrEmpty(fileName))
+            {
+                var htmlFragment = GenerateHTMLFragment($"<img src=\"{fileName}\"/>");
+                data.SetData(DataFormats.Html, htmlFragment);
+            }
+            // The 'copy=true' argument means the MemoryStreams can be safely disposed after the operation
+            Clipboard.SetDataObject(data, true);
+        }
+
+        private static byte[] ConvertToDib(byte[] pngBytes = null)
+        {
+            byte[] bm32bData;
+            int width, height;
+
+            {
+                using var skBmp = SKBitmap.Decode(pngBytes);
+                width = skBmp.Width;
+                height = skBmp.Height;
+                using var rotated = new SKBitmap(new SKImageInfo(width, height, skBmp.ColorType));
+                using var canvas = new SKCanvas(rotated);
+                canvas.Scale(1, -1, 0, height / 2.0f);
+                canvas.DrawBitmap(skBmp, SKPoint.Empty);
+                canvas.Flush();
+                bm32bData = rotated.Bytes;
+            }
+
+            // BITMAPINFOHEADER struct for DIB.
+            const int hdrSize = 0x28;
+            var fullImage = new byte[hdrSize + 12 + bm32bData.Length];
+            //Int32 biSize;
+            WriteIntToByteArray(fullImage, 0x00, 4, true, hdrSize);
+            //Int32 biWidth;
+            WriteIntToByteArray(fullImage, 0x04, 4, true, (uint)width);
+            //Int32 biHeight;
+            WriteIntToByteArray(fullImage, 0x08, 4, true, (uint)height);
+            //Int16 biPlanes;
+            WriteIntToByteArray(fullImage, 0x0C, 2, true, 1);
+            //Int16 biBitCount;
+            WriteIntToByteArray(fullImage, 0x0E, 2, true, 32);
+            //BITMAPCOMPRESSION biCompression = BITMAPCOMPRESSION.BITFIELDS;
+            WriteIntToByteArray(fullImage, 0x10, 4, true, 3);
+            //Int32 biSizeImage;
+            WriteIntToByteArray(fullImage, 0x14, 4, true, (uint)bm32bData.Length);
+            // These are all 0. Since .net clears new arrays, don't bother writing them.
+            //Int32 biXPelsPerMeter = 0;
+            //Int32 biYPelsPerMeter = 0;
+            //Int32 biClrUsed = 0;
+            //Int32 biClrImportant = 0;
+
+            // The aforementioned "BITFIELDS": colour masks applied to the Int32 pixel value to get the R, G and B values.
+            WriteIntToByteArray(fullImage, hdrSize + 0, 4, true, 0x00FF0000);
+            WriteIntToByteArray(fullImage, hdrSize + 4, 4, true, 0x0000FF00);
+            WriteIntToByteArray(fullImage, hdrSize + 8, 4, true, 0x000000FF);
+            Buffer.BlockCopy(bm32bData, 0, fullImage, hdrSize + 12, bm32bData.Length);
+            return fullImage;
+        }
+
+        private static void WriteIntToByteArray(byte[] data, int startIndex, int bytes, bool littleEndian, uint value)
+        {
+            var lastByte = bytes - 1;
+
+            if (data.Length < startIndex + bytes)
+            {
+                throw new ArgumentOutOfRangeException(nameof(startIndex), "Data array is too small to write a " + bytes + "-byte value at offset " + startIndex + ".");
+            }
+
+            for (var index = 0; index < bytes; index++)
+            {
+                var offs = startIndex + (littleEndian ? index : lastByte - index);
+                data[offs] = (byte)(value >> 8 * index & 0xFF);
+            }
+        }
+
+        private static string GenerateHTMLFragment(string html)
+        {
+            var sb = new StringBuilder();
+
+            const string header = "Version:0.9\r\nStartHTML:<<<<<<<<<1\r\nEndHTML:<<<<<<<<<2\r\nStartFragment:<<<<<<<<<3\r\nEndFragment:<<<<<<<<<4\r\n";
+            const string startHTML = "<html>\r\n<body>\r\n";
+            const string startFragment = "<!--StartFragment-->";
+            const string endFragment = "<!--EndFragment-->";
+            const string endHTML = "\r\n</body>\r\n</html>";
+
+            sb.Append(header);
+
+            var startHTMLLength = header.Length;
+            var startFragmentLength = startHTMLLength + startHTML.Length + startFragment.Length;
+            var endFragmentLength = startFragmentLength + Encoding.UTF8.GetByteCount(html);
+            var endHTMLLength = endFragmentLength + endFragment.Length + endHTML.Length;
+
+            sb.Replace("<<<<<<<<<1", startHTMLLength.ToString("D10"));
+            sb.Replace("<<<<<<<<<2", endHTMLLength.ToString("D10"));
+            sb.Replace("<<<<<<<<<3", startFragmentLength.ToString("D10"));
+            sb.Replace("<<<<<<<<<4", endFragmentLength.ToString("D10"));
+
+            sb.Append(startHTML);
+            sb.Append(startFragment);
+            sb.Append(html);
+            sb.Append(endFragment);
+            sb.Append(endHTML);
+
+            return sb.ToString();
+        }
+    }
+}

FModel/ViewModels/Commands/ImageCommand.cs

@@ -1,9 +1,13 @@
-using System.Windows;
-using System.Windows.Media;
-using AdonisUI.Controls;
+using AdonisUI.Controls;
+
+using FModel.Extensions;
 using FModel.Framework;
 using FModel.Views.Resources.Controls;
 
+using System.IO;
+using System.Windows;
+using System.Windows.Media;
+
 namespace FModel.ViewModels.Commands
 {
     public class ImageCommand : ViewModelCommand<TabItem>
@@ -36,7 +40,7 @@ namespace FModel.ViewModels.Commands
                     break;
                 }
                 case "Copy":
-                    Clipboard.SetImage(contextViewModel.Image);
+                    ClipboardExtensions.SetClipboardImage(contextViewModel.ImageBuffer, Path.ChangeExtension(contextViewModel.Header, ".png"));
                     break;
                 case "Save":
                     contextViewModel.SaveImage(false);

FModel/ViewModels/TabControlViewModel.cs

@@ -115,6 +115,7 @@ namespace FModel.ViewModels
             }
         }
 
+        public byte[] ImageBuffer { get; set; }
         private BitmapImage _image;
         public BitmapImage Image
         {
@@ -201,7 +202,8 @@ namespace FModel.ViewModels
         
         public void SetImage(SKImage img)
         {
-            using var stream = img.Encode().AsStream();
+            using var data = img.Encode();
+            using var stream = new MemoryStream(ImageBuffer = data.ToArray(), false);
             var image = new BitmapImage();
             image.BeginInit();
             image.CacheOption = BitmapCacheOption.OnLoad;