[visibility_detector] add custom visible bounds

packages/visibility_detector/lib/src/render_visibility_detector.dart

@@ -90,6 +90,9 @@ mixin RenderVisibilityDetectorBase on RenderObject {
   /// The key for the corresponding [VisibilityDetector] widget.
   Key get key;
 
+  /// The customVisibleBounds for the corresponding [VisibilityDetector] widget.
+  Rect? get customVisibleBounds;
+
   VoidCallback? _compositionCallbackCanceller;
 
   VisibilityChangedCallback? _onVisibilityChanged;
@@ -208,7 +211,7 @@ mixin RenderVisibilityDetectorBase on RenderObject {
       ancestor = ancestor.parent;
     }
 
-    Rect clip = Rect.largest;
+    var clip = customVisibleBounds ?? Rect.largest;
     for (int index = ancestors.length - 1; index > 0; index -= 1) {
       final parent = ancestors[index];
       final child = ancestors[index - 1];
@@ -283,6 +286,7 @@ class RenderVisibilityDetector extends RenderProxyBox
     RenderBox? child,
     required this.key,
     required VisibilityChangedCallback? onVisibilityChanged,
+    this.customVisibleBounds,
   })  : assert(key != null),
         super(child) {
     _onVisibilityChanged = onVisibilityChanged;
@@ -291,6 +295,9 @@ class RenderVisibilityDetector extends RenderProxyBox
   @override
   final Key key;
 
+  @override
+  Rect? customVisibleBounds;
+
   @override
   Rect? get bounds => hasSize ? semanticBounds : null;
 }
@@ -306,13 +313,17 @@ class RenderSliverVisibilityDetector extends RenderProxySliver
     RenderSliver? sliver,
     required this.key,
     required VisibilityChangedCallback? onVisibilityChanged,
+    this.customVisibleBounds,
   }) : super(sliver) {
     _onVisibilityChanged = onVisibilityChanged;
   }
 
   @override
   final Key key;
 
+  @override
+  Rect? customVisibleBounds;
+
   @override
   Rect? get bounds {
     if (geometry == null) {

packages/visibility_detector/lib/src/visibility_detector.dart

@@ -31,19 +31,24 @@ class VisibilityDetector extends SingleChildRenderObjectWidget {
     required Key key,
     required Widget child,
     required this.onVisibilityChanged,
+    this.customVisibleBounds,
   })  : assert(key != null),
         assert(child != null),
         super(key: key, child: child);
 
   /// The callback to invoke when this widget's visibility changes.
   final VisibilityChangedCallback? onVisibilityChanged;
 
+  /// Custom visible bounds to use for this widget.
+  final Rect? customVisibleBounds;
+
   /// See [RenderObjectWidget.createRenderObject].
   @override
   RenderVisibilityDetector createRenderObject(BuildContext context) {
     return RenderVisibilityDetector(
       key: key!,
       onVisibilityChanged: onVisibilityChanged,
+      customVisibleBounds: customVisibleBounds,
     );
   }
 
@@ -52,7 +57,9 @@ class VisibilityDetector extends SingleChildRenderObjectWidget {
   void updateRenderObject(
       BuildContext context, RenderVisibilityDetector renderObject) {
     assert(renderObject.key == key);
-    renderObject.onVisibilityChanged = onVisibilityChanged;
+    renderObject
+      ..onVisibilityChanged = onVisibilityChanged
+      ..customVisibleBounds = customVisibleBounds;
   }
 }
 
@@ -68,19 +75,24 @@ class SliverVisibilityDetector extends SingleChildRenderObjectWidget {
     required Key key,
     required Widget sliver,
     required this.onVisibilityChanged,
+    this.customVisibleBounds,
   })  : assert(key != null),
         assert(sliver != null),
         super(key: key, child: sliver);
 
   /// The callback to invoke when this widget's visibility changes.
   final VisibilityChangedCallback? onVisibilityChanged;
 
+  /// Custom visible bounds to use for this widget.
+  final Rect? customVisibleBounds;
+
   /// See [RenderObjectWidget.createRenderObject].
   @override
   RenderSliverVisibilityDetector createRenderObject(BuildContext context) {
     return RenderSliverVisibilityDetector(
       key: key!,
       onVisibilityChanged: onVisibilityChanged,
+      customVisibleBounds: customVisibleBounds,
     );
   }
 
@@ -89,7 +101,9 @@ class SliverVisibilityDetector extends SingleChildRenderObjectWidget {
   void updateRenderObject(
       BuildContext context, RenderSliverVisibilityDetector renderObject) {
     assert(renderObject.key == key);
-    renderObject.onVisibilityChanged = onVisibilityChanged;
+    renderObject
+      ..onVisibilityChanged = onVisibilityChanged
+      ..customVisibleBounds = customVisibleBounds;
   }
 }