Make SDL3Clipboard support images

osu.Framework/Platform/SDL/SDL3Clipboard.cs

@@ -1,8 +1,13 @@
 // Copyright (c) ppy Pty Ltd <[email protected]>. Licensed under the MIT Licence.
 // See the LICENCE file in the repository root for full licence text.
 
+using System.IO;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+using System.Text;
 using SDL;
 using SixLabors.ImageSharp;
+using SixLabors.ImageSharp.Formats;
 
 namespace osu.Framework.Platform.SDL
 {
@@ -15,14 +20,104 @@ public class SDL3Clipboard : Clipboard
 
         public override void SetText(string text) => SDL3.SDL_SetClipboardText(text);
 
+        private static readonly ImageFormatManager image_format_manager = SixLabors.ImageSharp.Configuration.Default.ImageFormatsManager;
+
         public override Image<TPixel>? GetImage<TPixel>()
         {
-            return null;
+            byte[] buffer;
+
+            unsafe
+            {
+                // It appears that SDL_GetClipboardData still returns the clipboard data
+                // even if it doesn't have the mimetype that we requested.
+                // So instead we ensure it's at least not text before trying to get it.
+                if (SDL3.SDL_HasClipboardText() == SDL3.SDL_TRUE)
+                    return null;
+
+                byte* data = null;
+                nuint size = 0;
+
+                foreach (IImageFormat? imageFormat in image_format_manager.ImageFormats)
+                {
+                    foreach (string mimeType in imageFormat.MimeTypes)
+                    {
+                        fixed (byte* zmimeType = Encoding.UTF8.GetBytes(mimeType + '\0'))
+                        {
+                            data = (byte*)SDL3.SDL_GetClipboardData(zmimeType, &size);
+                        }
+
+                        if (data != null)
+                            break;
+                    }
+
+                    if (data != null)
+                        break;
+                }
+
+                if (data == null)
+                    return null;
+
+                buffer = new byte[size];
+                Marshal.Copy((nint)data, buffer, 0, (int)size);
+
+                SDL3.SDL_free(data);
+            }
+
+            return Image.Load<TPixel>(buffer);
         }
 
+        // Used by the clipboard callbacks to access the image that has to be copied.
+        // When SetImage is called, the previous image is not immediately cleaned up
+        // by the cleanup callback (it is called only after we create the next image),
+        // which is why there are two of them to allow some overlap.
+        private static readonly Image?[] cb_images = { null, null };
+        private static int currentCbImageIdx;
+
         public override bool SetImage(Image image)
         {
-            return false;
+            unsafe
+            {
+                currentCbImageIdx = currentCbImageIdx == 0 ? 1 : 0;
+                cb_images[currentCbImageIdx] = image;
+
+                fixed (byte* pngMimeTypePtr = "image/png\0"u8)
+                {
+                    int status = SDL3.SDL_SetClipboardData(&clipboardDataCallback, &clipboardCleanupCallback, currentCbImageIdx, &pngMimeTypePtr, 1);
+                    return status == 0;
+                }
+            }
+        }
+
+        [UnmanagedCallersOnly(CallConvs = new[] { typeof(CallConvCdecl) })]
+        private static unsafe nint clipboardDataCallback(nint userdata, byte* mimetype, nuint* length)
+        {
+            Image? image = cb_images[(int)userdata];
+            if (image == null)
+                return 0;
+
+            string? mimeType = SDL3.PtrToStringUTF8(mimetype);
+            if (mimeType == null)
+                return 0;
+
+            image_format_manager.TryFindFormatByMimeType(mimeType, out IImageFormat? imageFormat);
+            if (imageFormat == null)
+                return 0;
+
+            MemoryStream imgStream = new MemoryStream();
+            image.Save(imgStream, imageFormat);
+            byte[] buffer = imgStream.GetBuffer();
+
+            byte* rawBuffer = (byte*)SDL3.SDL_malloc((nuint)buffer.Length);
+            Marshal.Copy(buffer, 0, (nint)rawBuffer, buffer.Length);
+
+            *length = (nuint)buffer.Length;
+            return (nint)rawBuffer;
+        }
+
+        [UnmanagedCallersOnly(CallConvs = new[] { typeof(CallConvCdecl) })]
+        private static void clipboardCleanupCallback(nint userdata)
+        {
+            cb_images[(int)userdata] = null;
         }
     }
 }