fix: correct jellyfin trickplay sheet geometry

close #1417

lib/services/jellyfin_trickplay_service.dart

@@ -1,4 +1,3 @@
-import 'dart:math' as math;
 import 'dart:ui';
 
 import 'package:cached_network_image_ce/cached_network_image.dart';
@@ -77,9 +76,8 @@ class JellyfinTrickplayService implements ScrubPreviewSource {
   }
 
   /// Pure math helper exposed for unit tests: maps a timestamp to the
-  /// sheet index, tile coordinates within the sheet, and the sheet's
+  /// sheet index, tile coordinates within the sheet, and the sheet's full
-  /// (possibly partial) row/column count. Returns `null` only when the
+  /// row/column count. Returns `null` only when the manifest is degenerate.
-  /// manifest is degenerate.
   TrickplayTileLocation? tileLocationFor(Duration time) {
     if (_disposed) return null;
     final info = _info;
@@ -94,17 +92,12 @@ class JellyfinTrickplayService implements ScrubPreviewSource {
     final tileColumn = tileInSheet % info.tileWidth;
     final tileRow = tileInSheet ~/ info.tileWidth;
 
-    final firstThumbInSheet = sheetIndex * tilesPerSheet;
-    final thumbsInSheet = math.min(tilesPerSheet, info.thumbnailCount - firstThumbInSheet);
-    final sheetColumns = thumbsInSheet >= info.tileWidth ? info.tileWidth : thumbsInSheet;
-    final sheetRows = (thumbsInSheet + info.tileWidth - 1) ~/ info.tileWidth;
-
     return TrickplayTileLocation(
       sheetIndex: sheetIndex,
       tileColumn: tileColumn,
       tileRow: tileRow,
-      sheetColumns: sheetColumns,
+      sheetColumns: info.tileWidth,
-      sheetRows: sheetRows,
+      sheetRows: info.tileHeight,
       sourceTileSize: Size(info.width.toDouble(), info.height.toDouble()),
     );
   }
@@ -176,9 +169,9 @@ class JellyfinTrickplayService implements ScrubPreviewSource {
 }
 
 /// Pure data: which sheet to fetch, which tile within it to display, the
-/// sheet's (possibly partial) row/column count, and the source tile's
+/// sheet's row/column count, and the source tile's pixel dimensions for
-/// pixel dimensions for aspect-correct scaling at render time. Returned
+/// aspect-correct scaling at render time. Returned by
-/// by [JellyfinTrickplayService.tileLocationFor] for unit tests.
+/// [JellyfinTrickplayService.tileLocationFor] for unit tests.
 class TrickplayTileLocation {
   final int sheetIndex;
   final int tileColumn;

test/services/jellyfin_trickplay_service_test.dart

@@ -95,7 +95,7 @@ void main() {
     // 250 thumbnails, 1s apart, 10×10 tiles per sheet ⇒ 3 sheets.
     // sheet 0: indices 0..99
     // sheet 1: indices 100..199 (full)
-    // sheet 2: indices 200..249 (last sheet, only 50 thumbs ⇒ 5 rows)
+    // sheet 2: indices 200..249 (last sheet, padded to a full 10x10 grid)
 
     setUp(() async {
       client = await JellyfinClient.create(_conn());
@@ -143,9 +143,10 @@ void main() {
       expect(loc.sheetIndex, 2);
       expect(loc.tileColumn, 9);
       expect(loc.tileRow, 4);
-      // Sheet 2 has 50 thumbs ⇒ 5 rows, full 10 cols
+      // Jellyfin pads the final tile image to the full configured grid, so
+      // the renderer must keep full sheet geometry even for partial sheets.
       expect(loc.sheetColumns, 10);
-      expect(loc.sheetRows, 5);
+      expect(loc.sheetRows, 10);
     });
 
     test('clamps past the end to the last available thumbnail', () {
@@ -168,7 +169,7 @@ void main() {
     });
   });
 
-  group('JellyfinTrickplayService — partial last sheet sizing', () {
+  group('JellyfinTrickplayService — padded last sheet sizing', () {
     late JellyfinClient client;
 
     setUp(() async {
@@ -177,7 +178,7 @@ void main() {
 
     tearDown(() => client.close());
 
-    test('last sheet with 1 thumbnail reports 1 col × 1 row', () {
+    test('last sheet with 1 thumbnail still reports the full sheet grid', () {
       // 17 thumbs, 4×4 sheet ⇒ sheet 0 full (16), sheet 1 has 1 thumb only.
       final svc = JellyfinTrickplayService.create(
         client: client,
@@ -192,8 +193,8 @@ void main() {
       expect(loc.sheetIndex, 1);
       expect(loc.tileColumn, 0);
       expect(loc.tileRow, 0);
-      expect(loc.sheetColumns, 1);
+      expect(loc.sheetColumns, 4);
-      expect(loc.sheetRows, 1);
+      expect(loc.sheetRows, 4);
     });
   });