refactor: Improve the export feature to capture actively selected strokes only if there is one

Author: TruePadawan

Scribble/Messages/DocumentMessages.cs Scribble/Messages/CanvasMessages.csScribble/Messages/DocumentMessages.cs renamed to Scribble/Messages/CanvasMessages.cs

@@ -17,4 +17,10 @@ public class RequestCanvasDataMessage : RequestMessage<CanvasDataPayload>
 public record LoadCanvasDataMessage(List<Stroke> Strokes, string? BackgroundColorHex);
 
 // Message from Document View Model to MainViewModel asking to clear the canvas
-public record ClearCanvasMessage();
+public record ClearCanvasMessage;
+
+public record SelectedStrokesPayload(List<DrawStroke> Strokes);
+
+public class RequestSelectedStrokes : RequestMessage<SelectedStrokesPayload>
+{
+}

Scribble/ViewModels/CanvasExportViewModel.cs

@@ -46,19 +46,32 @@ private void ChangeImageScale(string value)
         UpdateCanvasPreview();
     }
 
+    /// <summary>
+    /// Updates the preview image based on the current canvas state
+    /// If there is an active selection, it will be used as the preview else the entire canvas will be used
+    /// </summary>
     public void UpdateCanvasPreview()
     {
+        List<DrawStroke> previewedStrokes = [];
+        var strokesPayload = WeakReferenceMessenger.Default.Send<RequestSelectedStrokes>().Response;
         var canvasData = WeakReferenceMessenger.Default.Send<RequestCanvasDataMessage>().Response;
-        List<DrawStroke> drawStrokes = [];
-        foreach (var canvasStroke in canvasData.Strokes)
+
+        if (strokesPayload.Strokes.Count > 0)
         {
-            if (canvasStroke is DrawStroke drawStroke)
+            previewedStrokes = strokesPayload.Strokes;
+        }
+        else
+        {
+            foreach (var canvasStroke in canvasData.Strokes)
             {
-                drawStrokes.Add(drawStroke);
+                if (canvasStroke is DrawStroke drawStroke)
+                {
+                    previewedStrokes.Add(drawStroke);
+                }
             }
         }
 
-        var pngData = GetImageData(drawStrokes,
+        var pngData = GetImageData(previewedStrokes,
             includeBackground: IncludeBackground,
             backgroundColor: Utilities.ToSkColor(canvasData.BackgroundColor),
             ImageScale, SKEncodedImageFormat.Png);

Scribble/ViewModels/MainViewModel.cs

@@ -88,6 +88,32 @@ public MainViewModel(MultiUserDrawingViewModel multiplayer, DocumentViewModel do
         // Clear data when the DocumentViewModel triggers a reset
         WeakReferenceMessenger.Default.Register<MainViewModel, ClearCanvasMessage>(this,
             (mainViewModel, m) => { mainViewModel.ApplyEvent(new LoadCanvasEvent(Guid.NewGuid(), [])); });
+
+        // Send the actively selected strokes to the recipient
+        WeakReferenceMessenger.Default.Register<MainViewModel, RequestSelectedStrokes>(this,
+            (mainViewModel, message) =>
+            {
+                var hasActiveSelection = mainViewModel.SelectionTargets.Count > 0;
+                if (hasActiveSelection)
+                {
+                    var id = mainViewModel.SelectionTargets.Keys.First();
+                    var selectedStrokesIds = mainViewModel.SelectionTargets[id];
+                    List<DrawStroke> selectedStrokes = [];
+                    foreach (var stroke in mainViewModel.CanvasStrokes)
+                    {
+                        if (stroke is DrawStroke drawStroke && selectedStrokesIds.Contains(drawStroke.Id))
+                        {
+                            selectedStrokes.Add(drawStroke);
+                        }
+                    }
+
+                    message.Reply(new SelectedStrokesPayload(selectedStrokes));
+                }
+                else
+                {
+                    message.Reply(new SelectedStrokesPayload([]));
+                }
+            });
     }
 
     // Event handler for when another client in the room draws something