scrolling to entry with custom sliver list

lib/widgets/album/grid/list_section_layout.dart

@@ -1,18 +1,18 @@
 import 'dart:math';
 
 import 'package:aves/model/collection_lens.dart';
+import 'package:aves/model/image_entry.dart';
 import 'package:aves/widgets/album/grid/header_generic.dart';
 import 'package:aves/widgets/album/grid/list_sliver.dart';
 import 'package:flutter/material.dart';
 import 'package:provider/provider.dart';
 
 class SectionedListLayoutProvider extends StatelessWidget {
-  final Widget child;
-
   final CollectionLens collection;
   final int columnCount;
   final double scrollableWidth;
   final double tileExtent;
+  final Widget child;
 
   SectionedListLayoutProvider({
     @required this.collection,
@@ -64,7 +64,12 @@ class SectionedListLayoutProvider extends StatelessWidget {
         ),
       );
     });
-    return SectionedListLayout(sectionLayouts);
+    return SectionedListLayout(
+      collection: collection,
+      columnCount: columnCount,
+      tileExtent: tileExtent,
+      sectionLayouts: sectionLayouts,
+    );
   }
 
   Widget _buildInSection(int sectionChildIndex, CollectionLens collection, dynamic sectionKey) {
@@ -100,9 +105,37 @@ class SectionedListLayoutProvider extends StatelessWidget {
 }
 
 class SectionedListLayout {
+  final CollectionLens collection;
+  final int columnCount;
+  final double tileExtent;
   final List<SectionLayout> sectionLayouts;
 
-  const SectionedListLayout(this.sectionLayouts);
+  const SectionedListLayout({
+    @required this.collection,
+    @required this.columnCount,
+    @required this.tileExtent,
+    @required this.sectionLayouts,
+  });
+
+  Rect getTileRect(ImageEntry entry) {
+    final section = collection.sections.entries.firstWhere((kv) => kv.value.contains(entry), orElse: () => null);
+    if (section == null) return null;
+
+    final sectionKey = section.key;
+    final sectionLayout = sectionLayouts.firstWhere((sl) => sl.sectionKey == sectionKey, orElse: () => null);
+    if (sectionLayout == null) return null;
+
+    final showHeaders = collection.showHeaders;
+    final sectionEntryIndex = section.value.indexOf(entry);
+    final column = sectionEntryIndex % columnCount;
+    final row = (sectionEntryIndex / columnCount).floor();
+    final listIndex = sectionLayout.firstIndex + (showHeaders ? 1 : 0) + row;
+
+    final left = tileExtent * column;
+    final top = sectionLayout.indexToLayoutOffset(listIndex);
+    debugPrint('TLAD getTileRect sectionKey=$sectionKey sectionOffset=${sectionLayout.minOffset} top=$top row=$row column=$column for title=${entry.bestTitle}');
+    return Rect.fromLTWH(left, top, tileExtent, tileExtent);
+  }
 }
 
 class SectionLayout {

lib/widgets/album/grid/scaling.dart

@@ -2,12 +2,14 @@ import 'dart:math';
 import 'dart:ui' as ui;
 
 import 'package:aves/model/image_entry.dart';
+import 'package:aves/widgets/album/grid/list_section_layout.dart';
 import 'package:aves/widgets/album/grid/list_sliver.dart';
 import 'package:aves/widgets/album/grid/tile_extent_manager.dart';
 import 'package:aves/widgets/album/thumbnail.dart';
 import 'package:aves/widgets/common/data_providers/media_query_data_provider.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
+import 'package:provider/provider.dart';
 
 class GridScaleGestureDetector extends StatefulWidget {
   final GlobalKey scrollableKey;
@@ -33,7 +35,6 @@ class _GridScaleGestureDetectorState extends State<GridScaleGestureDetector> {
   ValueNotifier<double> _scaledExtentNotifier;
   OverlayEntry _overlayEntry;
   ThumbnailMetadata _metadata;
-  RenderSliver _renderSliver;
   RenderViewport _renderViewport;
 
   ValueNotifier<double> get tileExtentNotifier => widget.extentNotifier;
@@ -56,7 +57,6 @@ class _GridScaleGestureDetectorState extends State<GridScaleGestureDetector> {
         final renderMetaData = firstOf<RenderMetaData>(result);
         // abort if we cannot find an image to show on overlay
         if (renderMetaData == null) return;
-        _renderSliver = firstOf<RenderSliver>(result);
         _renderViewport = firstOf<RenderViewport>(result);
         _metadata = renderMetaData.metaData;
         _startExtent = tileExtentNotifier.value;
@@ -105,18 +105,18 @@ class _GridScaleGestureDetectorState extends State<GridScaleGestureDetector> {
 
         // TODO TLAD fix scroll to specific thumbnail with custom SliverList
         // scroll to show the focal point thumbnail at its new position
-        final sliverClosure = _renderSliver;
         final viewportClosure = _renderViewport;
-        final index = _metadata.index;
         WidgetsBinding.instance.addPostFrameCallback((_) {
           final scrollableContext = widget.scrollableKey.currentContext;
           final gridSize = (scrollableContext.findRenderObject() as RenderBox).size;
-          final newColumnCount = gridSize.width / newExtent;
+          final sectionLayout = Provider.of<SectionedListLayout>(context, listen: false);
-          final row = index ~/ newColumnCount;
+          final tileRect = sectionLayout.getTileRect(_metadata.entry);
+          final scrollOffset = (tileRect?.top ?? 0) - gridSize.height / 2;
+          viewportClosure.offset.jumpTo(scrollOffset.clamp(.0, double.infinity));
+          // about scrolling & offset retrieval:
           // `Scrollable.ensureVisible` only works on already rendered objects
           // `RenderViewport.showOnScreen` can find any `RenderSliver`, but not always a `RenderMetadata`
-          final scrollOffset = viewportClosure.scrollOffsetOf(sliverClosure, (row + 1) * newExtent - gridSize.height / 2);
+          // `RenderViewport.scrollOffsetOf` is a good alternative
-          viewportClosure.offset.jumpTo(scrollOffset.clamp(.0, double.infinity));
         });
       },
       child: widget.child,

lib/widgets/album/thumbnail_collection.dart

@@ -44,23 +44,23 @@ class ThumbnailCollection extends StatelessWidget {
             builder: (context, collection, child) {
               final scrollView = _buildScrollView(collection);
               final draggable = _buildDraggableScrollView(scrollView);
+              final scaler = GridScaleGestureDetector(
+                scrollableKey: _scrollableKey,
+                extentNotifier: _tileExtentNotifier,
+                mqSize: mqSize,
+                mqHorizontalPadding: mqHorizontalPadding,
+                child: draggable,
+              );
               final sectionedListLayoutProvider = ValueListenableBuilder<double>(
                 valueListenable: _tileExtentNotifier,
                 builder: (context, tileExtent, child) => SectionedListLayoutProvider(
                   collection: collection,
                   scrollableWidth: mqSize.width - mqHorizontalPadding,
                   tileExtent: tileExtent,
-                  child: draggable,
+                  child: scaler,
                 ),
               );
-              final scaler = GridScaleGestureDetector(
+              return sectionedListLayoutProvider;
-                scrollableKey: _scrollableKey,
-                extentNotifier: _tileExtentNotifier,
-                mqSize: mqSize,
-                mqHorizontalPadding: mqHorizontalPadding,
-                child: sectionedListLayoutProvider,
-              );
-              return scaler;
             },
           );
         },