StaticImageRenderer: mipmap pyramid for smooth zoom; add Anisotropic scaling option (#177)

Replace the full-res-every-frame draw path with a pre-generated mipmap
pyramid (0.5x ... 1/32x source) built on a background Task at load time.
Draw() selects the smallest level whose pixel dimensions still exceed the
display size, so zoom animations sample a level close to screen size
instead of the full source - eliminating frame drops on large images at
high interpolation quality.

Remove the old offscreen buffer entirely; the mip chain serves both the
animating and static states.

Add Anisotropic as a new interpolation option between Bilinear and High
Quality Cubic (Settings -> Image Scaling Quality).

Mip generation snapshots the user's configured scaling quality so
NearestNeighbor pixel art is built and rendered correctly at all zoom
levels. Quality changes cancel and rebuild the mip chain immediately.

IRenderer changes:
- Remove the three offscreen methods
- Rename OnDeviceRecreated -> HandleScalingMethodChange (the old name
  implied full device-loss recovery, which is not done; cached
  CanvasBitmaps in the photo cache remain tied to the old device)
- MultiPageRenderer.HandleScalingMethodChange triggers an immediate
  redraw so the new quality takes effect without waiting for the next
  animation frame

Author: riyasy

Src/FlyPhotos/Core/Model/Enums.cs

@@ -68,7 +68,8 @@ public enum Setting
     CaptionButtonsAutoHideToggle,
     CtrlDragToMoveWindowToggle,
     AutoFadeToggle,
-    AutoHideMouseToggle
+    AutoHideMouseToggle,
+    ImageScalingQualityChange
 }
 
 public enum ScrollDirection
@@ -100,5 +101,6 @@ public enum ImageInterpolation
 {
     NearestNeighbor,
     Linear,
+    Anisotropic,
     HighQualityCubic
 }

Src/FlyPhotos/Display/Controllers/CanvasController.cs

@@ -75,12 +75,11 @@ internal class CanvasController : ICanvasController
     private bool _realImageDisplayedForCurrentPhoto;
     private bool _isMultiPageActive;
 
-    // W2D-owned: set inside the ZoomOutOnExit action, read in the AnimationCompleted handler.
+    // W2D-owned: set inside the ZoomOutOnExit action, read in WaitForPanZoomAnimationAsync.
     private bool _isGoingToExit;
 
     // W2D-owned: true while ZoomAtPointPrecision ticks are arriving (right-click continuous zoom).
-    // Cleared 700 ms after the last tick — just after the 650 ms offscreen timer fires — so Draw
-    // skips the offscreen and uses source-bitmap quality during the zoom burst.
+    // Treated as animating so Draw uses mip-based quality. Cleared 700 ms after the last tick.
     private bool _continuousZoomActive;
     private CancellationTokenSource _continuousZoomCts;
 
@@ -109,7 +108,6 @@ public CanvasController(CanvasAnimatedControl d2dCanvas, IThumbnailController th
             _d2dCanvas.DispatcherQueue.TryEnqueue(() => OnOneToOneStateChanged?.Invoke(isOneToOne));
         _canvasViewManager.ZoomChanged += RequestZoomUpdate;
         _canvasViewManager.ViewChanged += RequestInvalidate;
-        _canvasViewManager.AnimationCompleted += CanvasViewManager_AnimationCompleted;
     }
 
     public void Dispose()
@@ -207,8 +205,8 @@ private async Task HandleHqAnimatedDisplayItemAsync(int currentOperationId, Phot
         {
             // For animated images, first display the static first frame immediately for responsiveness.
             InstallRenderer(
-                new StaticImageRenderer(_d2dCanvas, _canvasViewState, animDispItem.Bitmap,
-                    photo.SupportsTransparency, RequestInvalidate, createOffScreen: false),
+                new StaticImageRenderer(_d2dCanvas, animDispItem.Bitmap,
+                    photo.SupportsTransparency, RequestInvalidate, generateMipChain: false),
                 _imageSize, animDispItem.Rotation, ctx, forceThumbNailRedraw: true);
 
             // Asynchronously create the appropriate animator (GIF, WebP, APNG, or AVIF).
@@ -247,7 +245,7 @@ private async Task HandleHqAnimatedDisplayItemAsync(int currentOperationId, Phot
     private void HandleHqStaticDisplayItem(Photo photo, HqDisplayItem hqDispItem, PhotoInstallContext ctx)
     {
         InstallRenderer(
-            new StaticImageRenderer(_d2dCanvas, _canvasViewState, hqDispItem.Bitmap,
+            new StaticImageRenderer(_d2dCanvas, hqDispItem.Bitmap,
                 photo.SupportsTransparency, RequestInvalidate),
             _imageSize, hqDispItem.Rotation, ctx, forceThumbNailRedraw: true);
     }
@@ -269,8 +267,8 @@ private void HandlePreviewDisplayItem(Photo photo, PreviewDisplayItem previewDis
         var correctedWidth = _imageSize.Height * previewAspectRatio;
 
         InstallRenderer(
-            new StaticImageRenderer(_d2dCanvas, _canvasViewState, previewDispItem.Bitmap,
-                photo.SupportsTransparency, RequestInvalidate, createOffScreen: false),
+            new StaticImageRenderer(_d2dCanvas, previewDispItem.Bitmap,
+                photo.SupportsTransparency, RequestInvalidate, generateMipChain: false),
             new Size(correctedWidth, _imageSize.Height), previewDispItem.Rotation, ctx, forceThumbNailRedraw: true);
     }
 
@@ -328,12 +326,6 @@ private void InstallRenderer(IRenderer newRenderer, Size imageSize,
 
             if (forceThumbNailRedraw)
                 _thumbNailController.CreateThumbnailRibbonOffScreen(); // self-marshals to the UI thread
-
-            // Skip the offscreen timer when an animation is starting — AnimationCompleted will call
-            // TryRedrawOffScreen(false) at the correct final scale. Starting the timer here while
-            // Scale is near-zero (startup zoom) would bake a tiny offscreen mid-animation.
-            if (!_canvasViewManager.PanZoomAnimationOnGoing)
-                _currentRenderer.RestartOffScreenDrawTimer();
         });
     }
 
@@ -344,7 +336,6 @@ public void FitToScreen(bool animateChange)
         EnqueueW2dAction(() =>
         {
             if (_currentRenderer == null) return;
-            if (animateChange) _currentRenderer.CancelOffScreenTimer();
             _canvasViewManager.ZoomPanToFit(animateChange, imageSize, canvasSize);
         });
     }
@@ -355,7 +346,7 @@ public void ZoomToHundred()
         EnqueueW2dAction(() =>
         {
             if (_currentRenderer == null) return;
-            _currentRenderer.CancelOffScreenTimer();
+
             _canvasViewManager.ZoomToHundred(canvasSize);
         });
     }
@@ -366,7 +357,7 @@ public void ZoomToHundred(Point anchor)
         EnqueueW2dAction(() =>
         {
             if (_currentRenderer == null) return;
-            _currentRenderer.CancelOffScreenTimer();
+
             _canvasViewManager.ZoomToHundred(canvasSize, anchor);
         });
     }
@@ -387,7 +378,7 @@ public void ZoomByKeyboard(ZoomDirection zoomDirection)
         EnqueueW2dAction(() =>
         {
             if (_currentRenderer == null) return;
-            _currentRenderer.CancelOffScreenTimer();
+
             _canvasViewManager.ZoomAtCenter(zoomDirection, canvasSize);
         });
     }
@@ -398,7 +389,7 @@ public void StepZoom(ZoomDirection zoomDirection, Point? zoomAnchor = null)
         EnqueueW2dAction(() =>
         {
             if (_currentRenderer == null) return;
-            _currentRenderer.CancelOffScreenTimer();
+
             _canvasViewManager.StepZoom(zoomDirection, canvasSize, zoomAnchor);
         });
     }
@@ -408,7 +399,7 @@ public void ZoomAtPoint(ZoomDirection zoomDirection, Point zoomAnchor)
         EnqueueW2dAction(() =>
         {
             if (_currentRenderer == null) return;
-            _currentRenderer.CancelOffScreenTimer();
+
             _canvasViewManager.ZoomAtPoint(zoomDirection, zoomAnchor);
         });
     }
@@ -420,13 +411,9 @@ public void ZoomAtPointPrecision(int delta, Point zoomAnchor)
             if (_currentRenderer == null) return;
             _canvasViewManager.ZoomAtPointPrecision(delta, zoomAnchor);
 
-            // No animation → no AnimationCompleted → must restart the offscreen timer manually
-            // so the offscreen is recreated 650ms after the last zoom tick.
-            _currentRenderer.RestartOffScreenDrawTimer();
-
-            // Mark the burst as active so D2dCanvas_Draw skips the offscreen and uses
-            // source-bitmap quality. Debounce the clear to 700ms (just after the 650ms
-            // offscreen timer) so Draw switches back to the fresh offscreen once zoom stops.
+            // Mark the burst as active so the render path uses mip-based quality instead of
+            // source-bitmap quality. Debounced 700ms after the last tick so Draw reverts to
+            // non-animating mip selection once the zoom burst ends.
             _continuousZoomActive = true;
             _continuousZoomCts?.Cancel();
             _continuousZoomCts?.Dispose();
@@ -488,11 +475,12 @@ private void D2dCanvas_CreateResources(CanvasAnimatedControl sender,
         Microsoft.Graphics.Canvas.UI.CanvasCreateResourcesEventArgs args)
     {
         // Device (re)created (first load or device loss). Drop the device-bound brush so it is
-        // rebuilt lazily, and ask the current renderer to rebuild its off-screen surface.
+        // rebuilt lazily, and rebuild the mip chain with the current scaling quality.
+        // Note: CanvasBitmaps held in the photo cache are NOT re-created here (accepted risk).
         // Runs on the W2D thread.
         _checkeredBrush?.Dispose();
         _checkeredBrush = null;
-        _currentRenderer?.TryRedrawOffScreen(true);
+        _currentRenderer?.HandleScalingMethodChange();
     }
 
     /// <summary>
@@ -554,16 +542,9 @@ private void D2dCanvas_SizeChanged(object sender, SizeChangedEventArgs args)
         {
             if (_currentRenderer == null) return;
             _canvasViewManager.HandleSizeChange(newSize, previousSize);
-            _currentRenderer.RestartOffScreenDrawTimer();
         });
     }
 
-    private void CanvasViewManager_AnimationCompleted()
-    {
-        if (!_isGoingToExit)
-            _currentRenderer?.TryRedrawOffScreen(false);
-    }
-
     /// <summary>
     /// Returns a Task that completes when the next pan/zoom animation finishes (via the W2D-thread
     /// <see cref="CanvasViewManager.AnimationCompleted"/> event), or after <paramref name="timeoutMs"/>
@@ -613,7 +594,12 @@ public bool IsPressedOnImage(Point position)
 
     public void HandleCheckeredBackgroundChange()
     {
-        EnqueueW2dAction(() => _currentRenderer?.TryRedrawOffScreen(true));
+        EnqueueW2dAction(() => { }); // wake the canvas; Draw() reads the setting live
+    }
+
+    public void HandleImageScalingQualityChange()
+    {
+        EnqueueW2dAction(() => _currentRenderer?.HandleScalingMethodChange());
     }
 
     /// <summary>

Src/FlyPhotos/Display/ImageRendering/AnimatedImageRenderer.cs

@@ -92,9 +92,7 @@ private async Task UpdateFrameAsync()
         }
     }
 
-    public void RestartOffScreenDrawTimer() { }
-    public void CancelOffScreenTimer() { }
-    public void TryRedrawOffScreen(bool forceCreate) { }
+    public void HandleScalingMethodChange() { }
 
     public void Dispose()
     {

Src/FlyPhotos/Display/ImageRendering/IRenderer.cs

@@ -14,9 +14,9 @@ internal interface IRenderer : IDisposable
     /// </summary>
     void Draw(CanvasDrawingSession session, CanvasViewState viewState, CanvasImageInterpolation quality, bool isAnimating);
 
-    void RestartOffScreenDrawTimer();
-
-    void CancelOffScreenTimer();
-
-    void TryRedrawOffScreen(bool forceCreate);
+    /// <summary>
+    /// Called when the image scaling quality setting changes. Renderers that cache scaled
+    /// GPU resources (e.g. mip chains) should rebuild them with the new quality.
+    /// </summary>
+    void HandleScalingMethodChange();
 }

Src/FlyPhotos/Display/ImageRendering/MultiPageRenderer.cs

@@ -93,9 +93,7 @@ public void Draw(CanvasDrawingSession session, CanvasViewState viewState, Canvas
         }
     }
 
-    public void RestartOffScreenDrawTimer() { }
-    public void CancelOffScreenTimer() { }
-    public void TryRedrawOffScreen(bool forceCreate) { }
+    public void HandleScalingMethodChange() => _invalidate();
 
     public void Dispose()
     {