Add filterQuality property to improve image quality after scale

example/lib/screens/examples/full_screen_examples.dart

@@ -30,6 +30,21 @@ class FullScreenExamples extends StatelessWidget {
                     );
                   },
                 ),
+                ExampleButtonNode(
+                  title: "Large Image (filter quality: medium)",
+                  onPressed: () {
+                    Navigator.push(
+                      context,
+                      MaterialPageRoute(
+                        builder: (context) => const FullScreenWrapper(
+                          imageProvider:
+                              const AssetImage("assets/large-image.jpg"),
+                          filterQuality: FilterQuality.medium,
+                        ),
+                      ),
+                    );
+                  },
+                ),
                 ExampleButtonNode(
                   title: "Small Image (custom background)",
                   onPressed: () {
@@ -200,6 +215,7 @@ class FullScreenWrapper extends StatelessWidget {
     this.maxScale,
     this.initialScale,
     this.basePosition = Alignment.center,
+    this.filterQuality = FilterQuality.none,
   });
 
   final ImageProvider imageProvider;
@@ -209,6 +225,7 @@ class FullScreenWrapper extends StatelessWidget {
   final dynamic maxScale;
   final dynamic initialScale;
   final Alignment basePosition;
+  final FilterQuality filterQuality;
 
   @override
   Widget build(BuildContext context) {
@@ -224,6 +241,7 @@ class FullScreenWrapper extends StatelessWidget {
         maxScale: maxScale,
         initialScale: initialScale,
         basePosition: basePosition,
+        filterQuality: filterQuality,
       ),
     );
   }

lib/photo_view.dart

@@ -244,6 +244,7 @@ class PhotoView extends StatefulWidget {
     this.customSize,
     this.gestureDetectorBehavior,
     this.tightMode,
+    this.filterQuality,
   })  : child = null,
         childSize = null,
         super(key: key);
@@ -274,6 +275,7 @@ class PhotoView extends StatefulWidget {
     this.customSize,
     this.gestureDetectorBehavior,
     this.tightMode,
+    this.filterQuality,
   })  : loadingChild = null,
         imageProvider = null,
         gaplessPlayback = false,
@@ -357,6 +359,9 @@ class PhotoView extends StatefulWidget {
   /// Useful when inside a [Dialog]
   final bool tightMode;
 
+  /// Quality levels for image filters.
+  final FilterQuality filterQuality;
+
   @override
   State<StatefulWidget> createState() {
     return _PhotoViewState();
@@ -516,6 +521,7 @@ class _PhotoViewState extends State<PhotoView> {
       onTapDown: widget.onTapDown,
       gestureDetectorBehavior: widget.gestureDetectorBehavior,
       tightMode: widget.tightMode ?? false,
+      filterQuality: widget.filterQuality ?? FilterQuality.none,
     );
   }
 
@@ -570,6 +576,7 @@ class _PhotoViewState extends State<PhotoView> {
       onTapDown: widget.onTapDown,
       gestureDetectorBehavior: widget.gestureDetectorBehavior,
       tightMode: widget.tightMode ?? false,
+      filterQuality: widget.filterQuality ?? FilterQuality.none,
     );
   }
 

lib/photo_view_gallery.dart

@@ -237,6 +237,7 @@ class _PhotoViewGalleryState extends State<PhotoViewGallery> {
             onTapDown: pageOption.onTapDown,
             gestureDetectorBehavior: pageOption.gestureDetectorBehavior,
             tightMode: pageOption.tightMode,
+            filterQuality: pageOption.filterQuality,
           )
         : PhotoView(
             key: ObjectKey(index),
@@ -258,6 +259,7 @@ class _PhotoViewGalleryState extends State<PhotoViewGallery> {
             onTapDown: pageOption.onTapDown,
             gestureDetectorBehavior: pageOption.gestureDetectorBehavior,
             tightMode: pageOption.tightMode,
+            filterQuality: pageOption.filterQuality,
           );
 
     return ClipRect(
@@ -294,6 +296,7 @@ class PhotoViewGalleryPageOptions {
     this.onTapDown,
     this.gestureDetectorBehavior,
     this.tightMode,
+    this.filterQuality,
   })  : child = null,
         childSize = null,
         assert(imageProvider != null);
@@ -313,6 +316,7 @@ class PhotoViewGalleryPageOptions {
     this.onTapDown,
     this.gestureDetectorBehavior,
     this.tightMode,
+    this.filterQuality,
   })  : imageProvider = null,
         assert(child != null),
         assert(childSize != null);
@@ -361,4 +365,7 @@ class PhotoViewGalleryPageOptions {
 
   /// Mirror to [PhotoView.tightMode]
   final bool tightMode;
+
+  /// Quality levels for image filters.
+  final FilterQuality filterQuality;
 }

lib/src/core/photo_view_core.dart

@@ -36,6 +36,7 @@ class PhotoViewCore extends StatefulWidget {
     @required this.scaleStateController,
     @required this.basePosition,
     @required this.tightMode,
+    @required this.filterQuality,
   })  : customChild = null,
         super(key: key);
 
@@ -54,6 +55,7 @@ class PhotoViewCore extends StatefulWidget {
     @required this.scaleStateController,
     @required this.basePosition,
     @required this.tightMode,
+    @required this.filterQuality,
   })  : imageProvider = null,
         gaplessPlayback = false,
         super(key: key);
@@ -77,6 +79,8 @@ class PhotoViewCore extends StatefulWidget {
   final HitTestBehavior gestureDetectorBehavior;
   final bool tightMode;
 
+  final FilterQuality filterQuality;
+
   @override
   State<StatefulWidget> createState() {
     return PhotoViewCoreState();
@@ -282,9 +286,10 @@ class PhotoViewCoreState extends State<PhotoViewCore>
         ) {
           if (snapshot.hasData) {
             final PhotoViewControllerValue value = snapshot.data;
+            final useImageScale = widget.filterQuality != FilterQuality.none;
             final matrix = Matrix4.identity()
               ..translate(value.position.dx, value.position.dy)
-              ..scale(scale);
+              ..scale(useImageScale ? 1.0 : scale);
             if (widget.enableRotation) {
               matrix..rotateZ(value.rotation);
             }
@@ -293,6 +298,7 @@ class PhotoViewCoreState extends State<PhotoViewCore>
               delegate: _CenterWithOriginalSizeDelegate(
                 scaleBoundaries.childSize,
                 basePosition,
+                useImageScale,
               ),
               child: _buildHero(),
             );
@@ -343,28 +349,37 @@ class PhotoViewCoreState extends State<PhotoViewCore>
         : Image(
             image: widget.imageProvider,
             gaplessPlayback: widget.gaplessPlayback ?? false,
+            filterQuality: widget.filterQuality,
+            width: scaleBoundaries.childSize.width * scale,
+            fit: BoxFit.contain,
           );
   }
 }
 
 class _CenterWithOriginalSizeDelegate extends SingleChildLayoutDelegate {
-  const _CenterWithOriginalSizeDelegate(this.subjectSize, this.basePosition);
+  const _CenterWithOriginalSizeDelegate(
+      this.subjectSize, this.basePosition, this.useImageScale);
 
   final Size subjectSize;
   final Alignment basePosition;
+  final bool useImageScale;
 
   @override
   Offset getPositionForChild(Size size, Size childSize) {
     final double offsetX =
-        ((size.width - subjectSize.width) / 2) * (basePosition.x + 1);
-    final double offsetY =
-        ((size.height - subjectSize.height) / 2) * (basePosition.y + 1);
+        ((size.width - (useImageScale ? childSize.width : subjectSize.width)) /
+                2) *
+            (basePosition.x + 1);
+    final double offsetY = ((size.height -
+                (useImageScale ? childSize.height : subjectSize.height)) /
+            2) *
+        (basePosition.y + 1);
     return Offset(offsetX, offsetY);
   }
 
   @override
   BoxConstraints getConstraintsForChild(BoxConstraints constraints) {
-    return BoxConstraints.tight(subjectSize);
+    return useImageScale ? BoxConstraints() : BoxConstraints.tight(subjectSize);
   }
 
   @override