Making the first things work, still the ClipboardHelper needs to be modified so we do not return an image but a container, otherwise we cannot support vector graphics.

src/Greenshot.Base/Core/ClipboardHelper.cs

@@ -31,6 +31,7 @@ using System.Text;
 using System.Threading;
 using System.Windows.Forms;
 using Greenshot.Base.Core.Enums;
+using Greenshot.Base.Core.FileFormatHandlers;
 using Greenshot.Base.IniFile;
 using Greenshot.Base.Interfaces;
 using Greenshot.Base.Interfaces.Plugin;
@@ -1135,10 +1136,11 @@ EndSelection:<<<<<<<4
             string[] dropFileNames = (string[]) dataObject.GetData(DataFormats.FileDrop);
             if (dropFileNames != null && dropFileNames.Length > 0)
             {
+                var supportedExtensions = FileFormatHandlerRegistry.ExtensionsFor(FileFormatHandlerActions.LoadFromStream).ToList();
                 return dropFileNames
                     .Where(filename => !string.IsNullOrEmpty(filename))
                     .Where(Path.HasExtension)
-                    .Where(filename => ImageHelper.StreamConverters.Keys.Contains(Path.GetExtension(filename).ToLowerInvariant().Substring(1)));
+                    .Where(filename => supportedExtensions.Contains(Path.GetExtension(filename).ToLowerInvariant().Substring(1)));
             }
 
             return Enumerable.Empty<string>();

src/Greenshot.Base/Core/FileFormatHandlers/FileFormatHandlerRegistry.cs

@@ -0,0 +1,44 @@
+/*
+ * Greenshot - a free and open source screenshot tool
+ * Copyright (C) 2007-2021 Thomas Braun, Jens Klingen, Robin Krom
+ * 
+ * For more information see: https://getgreenshot.org/
+ * The Greenshot project is hosted on GitHub https://github.com/greenshot/greenshot
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 1 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+using System.Collections.Generic;
+using System.Linq;
+using Greenshot.Base.Interfaces;
+
+namespace Greenshot.Base.Core.FileFormatHandlers
+{
+    public static class FileFormatHandlerRegistry
+    {
+        public static readonly IList<IFileFormatHandler> FileFormatHandlers = new List<IFileFormatHandler>();
+
+        static FileFormatHandlerRegistry()
+        {
+            FileFormatHandlers.Add(new IconFileFormatHandler());
+            FileFormatHandlers.Add(new GreenshotFileFormatHandler());
+            FileFormatHandlers.Add(new DefaultFileFormatHandler());
+        }
+
+        public static IEnumerable<string> ExtensionsFor(FileFormatHandlerActions fileFormatHandlerAction)
+        {
+            return FileFormatHandlers.SelectMany(ffh => ffh.SupportedExtensions(fileFormatHandlerAction)).Distinct();
+        }
+    }
+}

src/Greenshot.Base/Core/FileFormatHandlers/GreenshotFileFormatHandler.cs

@@ -20,6 +20,7 @@
  */
 
 using System;
+using System.Collections.Generic;
 using System.Drawing;
 using System.IO;
 using System.Linq;
@@ -30,29 +31,51 @@ namespace Greenshot.Base.Core.FileFormatHandlers
 {
     public class GreenshotFileFormatHandler : IFileFormatHandler
     {
-        private static readonly string[] SupportedExtensions = { "greenshot" };
+        private static readonly string[] OurExtensions = { "greenshot" };
 
-        public bool CanDoActionForExtension(FileFormatHandlerActions fileFormatHandlerAction, string extension)
+        /// <inheritdoc />
+        public IEnumerable<string> SupportedExtensions(FileFormatHandlerActions fileFormatHandlerAction)
+        {
+            if (fileFormatHandlerAction == FileFormatHandlerActions.LoadDrawableFromStream)
+            {
+                return Enumerable.Empty<string>();
+            }
+
+            return OurExtensions;
+        }
+
+        /// <inheritdoc />
+        public bool Supports(FileFormatHandlerActions fileFormatHandlerAction, string extension)
         {
             if (fileFormatHandlerAction == FileFormatHandlerActions.LoadDrawableFromStream)
             {
                 return false;
             }
-            return SupportedExtensions.Contains(extension);
+
+            return OurExtensions.Contains(extension);
         }
 
-        public void SaveToStream(Bitmap bitmap, Stream destination, string extension)
+
+        /// <inheritdoc />
+        public int PriorityFor(FileFormatHandlerActions fileFormatHandlerAction, string extension)
         {
-            throw new NotImplementedException();
+            return int.MaxValue;
         }
 
-        public Bitmap Load(Stream stream, string extension)
+        public bool TrySaveToStream(Bitmap bitmap, Stream destination, string extension)
+        {
+            // TODO: Implement this
+            return false;
+        }
+
+        public bool TryLoadFromStream(Stream stream, string extension, out Bitmap bitmap)
         {
             var surface = SimpleServiceProvider.Current.GetInstance<Func<ISurface>>().Invoke();
-            return (Bitmap)surface.GetImageForExport();
+            bitmap = (Bitmap)surface.GetImageForExport();
+            return true;
         }
 
-        public IDrawableContainer LoadDrawableFromStream(Stream stream, string extension, ISurface parent)
+        public bool TryLoadDrawableFromStream(Stream stream, string extension, out IDrawableContainer drawableContainer, ISurface parent)
         {
             throw new NotImplementedException();
         }

src/Greenshot.Base/Core/FileFormatHandlers/PngFileFormatHandler.cs

@@ -20,6 +20,7 @@
  */
 
 using System;
+using System.Collections.Generic;
 using System.Drawing;
 using System.IO;
 using System.Linq;
@@ -28,31 +29,55 @@ using Greenshot.Base.Interfaces.Drawing;
 
 namespace Greenshot.Base.Core.FileFormatHandlers
 {
+    /// <summary>
+    /// This can be an ImageSharp implementation
+    /// </summary>
     public class PngFileFormatHandler : IFileFormatHandler
     {
-        private static readonly string[] SupportedExtensions = { "png" };
+        private static readonly string[] OurExtensions = { "png" };
 
-        public bool CanDoActionForExtension(FileFormatHandlerActions fileFormatHandlerAction, string extension)
+        /// <inheritdoc />
+        public IEnumerable<string> SupportedExtensions(FileFormatHandlerActions fileFormatHandlerAction)
+        {
+            if (fileFormatHandlerAction == FileFormatHandlerActions.LoadDrawableFromStream)
+            {
+                return Enumerable.Empty<string>();
+            }
+
+            return OurExtensions;
+        }
+
+        /// <inheritdoc />
+        public bool Supports(FileFormatHandlerActions fileFormatHandlerAction, string extension)
         {
             if (fileFormatHandlerAction == FileFormatHandlerActions.LoadDrawableFromStream)
             {
                 return false;
             }
-            return SupportedExtensions.Contains(extension);
+
+            return OurExtensions.Contains(extension);
+        }
+        /// <inheritdoc />
+        public int PriorityFor(FileFormatHandlerActions fileFormatHandlerAction, string extension)
+        {
+            return int.MaxValue;
         }
 
-        public void SaveToStream(Bitmap bitmap, Stream destination, string extension)
+        public bool TryLoadFromStream(Stream stream, string extension, out Bitmap bitmap)
         {
+            // TODO: Implement this
             throw new NotImplementedException();
         }
 
-        public Bitmap Load(Stream stream, string extension)
+        public bool TrySaveToStream(Bitmap bitmap, Stream destination, string extension)
         {
-            throw new NotImplementedException();
+            // TODO: Implement this
+            return false;
         }
 
-        public IDrawableContainer LoadDrawableFromStream(Stream stream, string extension, ISurface parent)
+        public bool TryLoadDrawableFromStream(Stream stream, string extension, out IDrawableContainer drawableContainer, ISurface parent)
         {
+            // TODO: Implement this
             throw new NotImplementedException();
         }
     }

src/Greenshot.Base/Core/ImageHelper.cs

@@ -25,6 +25,7 @@ using System.Drawing;
 using System.Drawing.Drawing2D;
 using System.Drawing.Imaging;
 using System.IO;
+using System.Linq;
 using Greenshot.Base.Core.FileFormatHandlers;
 using Greenshot.Base.Effects;
 using Greenshot.Base.IniFile;
@@ -56,14 +57,6 @@ namespace Greenshot.Base.Core
         private static readonly CoreConfiguration CoreConfig = IniConfig.GetIniSection<CoreConfiguration>();
         private const int ExifOrientationId = 0x0112;
 
-        public static readonly IList<IFileFormatHandler> FileFormatHandlers = new List<IFileFormatHandler>();
-
-        static ImageHelper()
-        {
-            FileFormatHandlers.Add(new IconFileFormatHandler());
-            FileFormatHandlers.Add(new GreenshotFileFormatHandler());
-            FileFormatHandlers.Add(new DefaultFileFormatHandler());
-        }
 
         /// <summary>
         /// Make sure the image is orientated correctly
@@ -1720,12 +1713,15 @@ namespace Greenshot.Base.Core
                 startingPosition = 0;
             }
 
-            foreach (var fileFormatHandler in FileFormatHandlers)
+            foreach (var fileFormatHandler in FileFormatHandlerRegistry.FileFormatHandlers
+                         .Where(ffh => ffh.Supports(FileFormatHandlerActions.LoadFromStream, extension))
+                         .OrderBy(ffh => ffh.PriorityFor(FileFormatHandlerActions.LoadFromStream, extension)))
             {
-                if (!fileFormatHandler.CanDoActionForExtension(FileFormatHandlerActions.Load, extension)) continue;
-
                 stream.Seek(startingPosition, SeekOrigin.Begin);
-                return fileFormatHandler.Load(stream, extension);
+                if (fileFormatHandler.TryLoadFromStream(stream, extension, out var bitmap))
+                {
+                    return bitmap;
+                }
             }
 
             return null;

src/Greenshot.Base/Core/NetworkHelper.cs

@@ -24,9 +24,11 @@ using System.Collections.Generic;
 using System.Drawing;
 using System.Globalization;
 using System.IO;
+using System.Linq;
 using System.Net;
 using System.Text;
 using System.Text.RegularExpressions;
+using Greenshot.Base.Core.FileFormatHandlers;
 using Greenshot.Base.IniFile;
 using Greenshot.Base.Interfaces;
 using Greenshot.Base.Interfaces.Plugin;
@@ -94,7 +96,8 @@ namespace Greenshot.Base.Core
         public static Image DownloadImage(string url)
         {
             var extensions = new StringBuilder();
-            foreach (var extension in ImageHelper.StreamConverters.Keys)
+            var supportedExtensions = FileFormatHandlerRegistry.ExtensionsFor(FileFormatHandlerActions.LoadFromStream).ToList();
+            foreach (var extension in supportedExtensions)
             {
                 if (string.IsNullOrEmpty(extension))
                 {

src/Greenshot.Base/Interfaces/IFileFormatHandler.cs

@@ -32,7 +32,7 @@ namespace Greenshot.Base.Interfaces
     public enum FileFormatHandlerActions
     {
         SaveToStream,
-        Load,
+        LoadFromStream,
         LoadDrawableFromStream
     }
 

src/Greenshot.Editor/EditorInitialize.cs

@@ -0,0 +1,34 @@
+/*
+ * Greenshot - a free and open source screenshot tool
+ * Copyright (C) 2007-2021 Thomas Braun, Jens Klingen, Robin Krom
+ * 
+ * For more information see: https://getgreenshot.org/
+ * The Greenshot project is hosted on GitHub https://github.com/greenshot/greenshot
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 1 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+using Greenshot.Base.Core.FileFormatHandlers;
+using Greenshot.Editor.FileFormatHandlers;
+
+namespace Greenshot.Editor
+{
+    public static class EditorInitialize
+    {
+        public static void Initialize()
+        {
+            FileFormatHandlerRegistry.FileFormatHandlers.Add(new SvgFileFormatHandler());
+        }
+    }
+}

src/Greenshot.Editor/FileFormatHandlers/SvgFileFormatHandler.cs

@@ -20,6 +20,7 @@
  */
 
 using System;
+using System.Collections.Generic;
 using System.Drawing;
 using System.Drawing.Imaging;
 using System.IO;
@@ -39,48 +40,67 @@ namespace Greenshot.Editor.FileFormatHandlers
     public class SvgFileFormatHandler : IFileFormatHandler
     {
         private static readonly ILog Log = LogManager.GetLogger(typeof(ImageHelper));
+        private static readonly string[] OurExtensions = { "svg" };
 
-        private static readonly string[] SupportedExtensions = { "svg" };
-
-        public bool CanDoActionForExtension(FileFormatHandlerActions fileFormatHandlerAction, string extension)
+        /// <inheritdoc />
+        public IEnumerable<string> SupportedExtensions(FileFormatHandlerActions fileFormatHandlerAction)
         {
-            if (fileFormatHandlerAction == FileFormatHandlerActions.SaveToStream)
+            if (fileFormatHandlerAction == FileFormatHandlerActions.LoadDrawableFromStream)
+            {
+                return Enumerable.Empty<string>();
+            }
+
+            return OurExtensions;
+        }
+
+        /// <inheritdoc />
+        public bool Supports(FileFormatHandlerActions fileFormatHandlerAction, string extension)
+        {
+            if (fileFormatHandlerAction == FileFormatHandlerActions.LoadDrawableFromStream)
             {
                 return false;
             }
-            return SupportedExtensions.Contains(extension);
+
+            return OurExtensions.Contains(extension);
+        }
+        /// <inheritdoc />
+        public int PriorityFor(FileFormatHandlerActions fileFormatHandlerAction, string extension)
+        {
+            return int.MaxValue;
         }
 
-        public void SaveToStream(Bitmap bitmap, Stream destination, string extension)
+        public bool TryLoadFromStream(Stream stream, string extension, out Bitmap bitmap)
         {
-            throw new NotImplementedException();
-        }
-
-        public Bitmap Load(Stream stream, string extension)
-        {
-
             var svgDocument = SvgDocument.Open<SvgDocument>(stream);
             int width = (int)svgDocument.ViewBox.Width;
             int height = (int)svgDocument.ViewBox.Height;
 
             try
             {
-                var result = ImageHelper.CreateEmpty(width, height, PixelFormat.Format32bppArgb, Color.Transparent);
-                svgDocument.Draw(result);
-                return result;
+                bitmap = ImageHelper.CreateEmpty(width, height, PixelFormat.Format32bppArgb, Color.Transparent);
+                svgDocument.Draw(bitmap);
+                return true;
             }
             catch (Exception ex)
             {
                 Log.Error("Can't load SVG", ex);
             }
 
-            return null;
+            bitmap = null;
+            return false;
         }
 
-        public IDrawableContainer LoadDrawableFromStream(Stream stream, string extension, ISurface parent)
+        public bool TrySaveToStream(Bitmap bitmap, Stream destination, string extension)
+        {
+            // TODO: Implement this
+            return false;
+        }
+
+        public bool TryLoadDrawableFromStream(Stream stream, string extension, out IDrawableContainer drawableContainer, ISurface parent)
         {
             var svgDocument = SvgDocument.Open<SvgDocument>(stream);
-            return new SvgContainer(svgDocument, parent);
+            drawableContainer = new SvgContainer(svgDocument, parent);
+            return true;
         }
     }
 }

src/Greenshot/GreenshotMain.cs

@@ -23,6 +23,7 @@ using System;
 using System.Globalization;
 using System.Net;
 using System.Reflection;
+using Greenshot.Editor;
 using Greenshot.Forms;
 
 namespace Greenshot
@@ -65,6 +66,7 @@ namespace Greenshot
             CultureInfo.DefaultThreadCurrentCulture = CultureInfo.InvariantCulture;
             CultureInfo.DefaultThreadCurrentUICulture = CultureInfo.InvariantCulture;
 
+            EditorInitialize.Initialize();
             MainForm.Start(args);
         }
     }