Merge branch 'classic-ui-modern-fixes' to fix webcam preview visibility

Merged improvements to webcam handling from classic-ui-modern-fixes branch:
- Added SetPreviewVisibility method to IWebcamCapture interface
- Improved webcam preview visibility control to avoid flicker
- Better camera lifecycle management with _acquired flag
- Preview now hides when page is not visible instead of releasing camera
- Added proper cleanup in Unloaded event handler

Resolved conflicts:
- src/Captura/Pages/SettingsPage.xaml.cs: Kept About navigation methods from current branch
- src/Captura/Pages/WebcamPlacementPreviewPage.xaml.cs: Merged preview visibility logic

Author: cursoragent

src/Captura.Base/Services/IWebcamCapture.cs

@@ -14,6 +14,9 @@ public interface IWebcamCapture : IDisposable
 
         void UpdatePreview(IWindow Window, Rectangle Location);
 
+        // Control preview window visibility without tearing down the camera graph
+        void SetPreviewVisibility(bool IsVisible);
+
         string GetCameraProperties();
     }
 }

src/Captura.Windows/Webcam/CaptureWebcam.cs

@@ -13,6 +13,7 @@ public class CaptureWebcam : ISampleGrabberCB, IDisposable
         #region Fields
         readonly Filter _videoDevice;
         readonly IntPtr _previewWindow;
+        IntPtr _currentOwner;
         readonly DummyForm _form;
         readonly Action _onClick;
         readonly object _lock = new object();
@@ -50,6 +51,7 @@ public CaptureWebcam(Filter VideoDevice, Action OnClick, IntPtr PreviewWindow)
             _form.Click += (s, e) => OnClick?.Invoke();
 
             _previewWindow = PreviewWindow != IntPtr.Zero ? PreviewWindow : _form.Handle;
+            _currentOwner = _previewWindow;
 
             BuildGraph();
         }
@@ -502,6 +504,7 @@ void SetupVideoWindow()
                         _videoWindow = null;
                         return;
                     }
+                    _currentOwner = _previewWindow;
                 }
                 catch
                 {
@@ -555,6 +558,48 @@ public void OnPreviewWindowResize(int X, int Y, int Width, int Height)
             }
         }
 
+        public void SetPreviewVisibility(bool isVisible)
+        {
+            lock (_lock)
+            {
+                if (_videoWindow == null)
+                    return;
+
+                try
+                {
+                    _videoWindow.put_Visible(isVisible ? OABool.True : OABool.False);
+                }
+                catch { }
+            }
+        }
+
+        public void UpdatePreviewWindow(IntPtr ownerHandle, Rectangle location)
+        {
+            lock (_lock)
+            {
+                if (_videoWindow != null)
+                {
+                    try
+                    {
+                        if (ownerHandle != IntPtr.Zero && _currentOwner != ownerHandle)
+                        {
+                            // Switch owner without rebuilding the graph
+                            _videoWindow.put_Visible(OABool.False);
+                            _videoWindow.put_Owner(ownerHandle);
+                            _currentOwner = ownerHandle;
+                            _videoWindow.put_Visible(OABool.True);
+                        }
+
+                        _videoWindow.SetWindowPosition(location.X, location.Y, location.Width, location.Height);
+                    }
+                    catch
+                    {
+                        // Ignore errors
+                    }
+                }
+            }
+        }
+
         #endregion
 
         #region Frame Capture

src/Captura.Windows/Webcam/WebcamCapture.cs

@@ -94,18 +94,22 @@ public void UpdatePreview(IWindow Window, Rectangle Location)
             {
                 try
                 {
-                    if (Window != null && _lastWin != Window.Handle)
+                    // Lazily create capture when first preview is requested
+                    if (_captureWebcam == null)
                     {
-                        // Recreate capture with new window handle
-                        _captureWebcam?.StopPreview();
-                        _captureWebcam?.Dispose();
-
-                        _captureWebcam = new CaptureWebcam(_filter, _onClick, Window.Handle);
+                        var handle = Window?.Handle ?? IntPtr.Zero;
+                        _captureWebcam = new CaptureWebcam(_filter, _onClick, handle);
                         _captureWebcam.StartPreview();
-
+                        _lastWin = handle;
+                    }
+                    else if (Window != null && _lastWin != Window.Handle)
+                    {
+                        // Switch owner handle without rebuilding the graph
+                        _captureWebcam.UpdatePreviewWindow(Window.Handle, Location);
                         _lastWin = Window.Handle;
                     }
 
+                    // Always update window position
                     _captureWebcam?.OnPreviewWindowResize(Location.X, Location.Y, Location.Width, Location.Height);
                 }
                 catch (COMException ex)
@@ -119,6 +123,21 @@ public void UpdatePreview(IWindow Window, Rectangle Location)
             });
         }
 
+        public void SetPreviewVisibility(bool isVisible)
+        {
+            if (_disposed)
+                return;
+
+            _syncContext.Run(() =>
+            {
+                try
+                {
+                    _captureWebcam?.SetPreviewVisibility(isVisible);
+                }
+                catch { }
+            });
+        }
+
         void HandleCameraException(Exception exception, string context)
         {
             // Common DirectShow/Windows error codes

src/Captura/Pages/WebcamPlacementPreviewPage.xaml.cs

@@ -71,6 +71,7 @@ async Task UpdateBackground()
         IReadOnlyReactiveProperty<IWebcamCapture> _webcamCapture;
         bool _setupComplete;
         bool _isReleasing;
+        bool _acquired;
 
         public void SetupPreview()
         {
@@ -81,24 +82,25 @@ public void SetupPreview()
 
             IsVisibleChanged += (S, E) =>
             {
-                if (IsVisible && _webcamCapture == null && !_isReleasing)
+                if (IsVisible && !_isReleasing)
                 {
-                    _webcamCapture = _webcamModel.InitCapture();
+                    if (_webcamCapture == null)
+                    {
+                        _webcamCapture = _webcamModel.InitCapture();
+                        _acquired = true;
+                    }
 
                     if (_webcamCapture.Value is { } capture)
                     {
                         _reactor.WebcamSize.OnNext(new WSize(capture.Width, capture.Height));
-
+                        _webcamCapture.Value.SetPreviewVisibility(true);
                         UpdateWebcamPreview();
                     }
                 }
                 else if (!IsVisible && _webcamCapture != null && !_isReleasing)
                 {
-                    // Release webcam when page becomes not visible
-                    _isReleasing = true;
-                    _webcamModel.ReleaseCapture();
-                    _webcamCapture = null;
-                    _isReleasing = false;
+                    // Hide preview when page is not visible but keep camera running to avoid flicker
+                    try { _webcamCapture.Value?.SetPreviewVisibility(false); } catch { }
                 }
             };
 
@@ -127,6 +129,19 @@ void OnRegionChange()
                 .AddTo(_subscriptions);
 
             UpdateWebcamPreview();
+
+            Unloaded += (s, e) =>
+            {
+                // Cleanup when page is unloaded
+                if (_acquired && _webcamCapture != null)
+                {
+                    _isReleasing = true;
+                    _webcamModel.ReleaseCapture();
+                    _webcamCapture = null;
+                    _acquired = false;
+                    _isReleasing = false;
+                }
+            };
         }