opt download (#1755)

Signed-off-by: bggRGjQaUbCoE <githubaccount56556@proton.me>

lib/utils/grid.dart

@@ -137,3 +137,106 @@ class SliverGridDelegateWithExtentAndRatio extends SliverGridDelegate {
     return flag;
   }
 }
+
+class SliverGridDelegateWithMaxCrossAxisExtent extends SliverGridDelegate {
+  /// Creates a delegate that makes grid layouts with tiles that have a maximum
+  /// cross-axis extent.
+  ///
+  /// The [maxCrossAxisExtent], [mainAxisExtent], [mainAxisSpacing],
+  /// and [crossAxisSpacing] arguments must not be negative.
+  /// The [childAspectRatio] argument must be greater than zero.
+  SliverGridDelegateWithMaxCrossAxisExtent({
+    required this.maxCrossAxisExtent,
+    this.mainAxisSpacing = 0.0,
+    this.crossAxisSpacing = 0.0,
+    this.childAspectRatio = 1.0,
+    this.mainAxisExtent,
+  }) : assert(maxCrossAxisExtent > 0),
+       assert(mainAxisSpacing >= 0),
+       assert(crossAxisSpacing >= 0),
+       assert(childAspectRatio > 0),
+       assert(mainAxisExtent == null || mainAxisExtent >= 0);
+
+  /// The maximum extent of tiles in the cross axis.
+  ///
+  /// This delegate will select a cross-axis extent for the tiles that is as
+  /// large as possible subject to the following conditions:
+  ///
+  ///  - The extent evenly divides the cross-axis extent of the grid.
+  ///  - The extent is at most [maxCrossAxisExtent].
+  ///
+  /// For example, if the grid is vertical, the grid is 500.0 pixels wide, and
+  /// [maxCrossAxisExtent] is 150.0, this delegate will create a grid with 4
+  /// columns that are 125.0 pixels wide.
+  final double maxCrossAxisExtent;
+
+  /// The number of logical pixels between each child along the main axis.
+  final double mainAxisSpacing;
+
+  /// The number of logical pixels between each child along the cross axis.
+  final double crossAxisSpacing;
+
+  /// The ratio of the cross-axis to the main-axis extent of each child.
+  final double childAspectRatio;
+
+  /// The extent of each tile in the main axis. If provided it would define the
+  /// logical pixels taken by each tile in the main-axis.
+  ///
+  /// If null, [childAspectRatio] is used instead.
+  final double? mainAxisExtent;
+
+  bool _debugAssertIsValid(double crossAxisExtent) {
+    assert(crossAxisExtent > 0.0);
+    assert(maxCrossAxisExtent > 0.0);
+    assert(mainAxisSpacing >= 0.0);
+    assert(crossAxisSpacing >= 0.0);
+    assert(childAspectRatio > 0.0);
+    return true;
+  }
+
+  SliverGridLayout? layoutCache;
+  double? crossAxisExtentCache;
+
+  @override
+  SliverGridLayout getLayout(SliverConstraints constraints) {
+    assert(_debugAssertIsValid(constraints.crossAxisExtent));
+    if (layoutCache != null &&
+        constraints.crossAxisExtent == crossAxisExtentCache) {
+      return layoutCache!;
+    }
+    crossAxisExtentCache = constraints.crossAxisExtent;
+    int crossAxisCount =
+        (constraints.crossAxisExtent / (maxCrossAxisExtent + crossAxisSpacing))
+            .ceil();
+    // Ensure a minimum count of 1, can be zero and result in an infinite extent
+    // below when the window size is 0.
+    crossAxisCount = max(1, crossAxisCount);
+    final double usableCrossAxisExtent = max(
+      0.0,
+      constraints.crossAxisExtent - crossAxisSpacing * (crossAxisCount - 1),
+    );
+    final double childCrossAxisExtent = usableCrossAxisExtent / crossAxisCount;
+    final double childMainAxisExtent =
+        mainAxisExtent ?? childCrossAxisExtent / childAspectRatio;
+    return layoutCache = SliverGridRegularTileLayout(
+      crossAxisCount: crossAxisCount,
+      mainAxisStride: childMainAxisExtent + mainAxisSpacing,
+      crossAxisStride: childCrossAxisExtent + crossAxisSpacing,
+      childMainAxisExtent: childMainAxisExtent,
+      childCrossAxisExtent: childCrossAxisExtent,
+      reverseCrossAxis: axisDirectionIsReversed(constraints.crossAxisDirection),
+    );
+  }
+
+  @override
+  bool shouldRelayout(SliverGridDelegateWithMaxCrossAxisExtent oldDelegate) {
+    final flag =
+        oldDelegate.maxCrossAxisExtent != maxCrossAxisExtent ||
+        oldDelegate.mainAxisSpacing != mainAxisSpacing ||
+        oldDelegate.crossAxisSpacing != crossAxisSpacing ||
+        oldDelegate.childAspectRatio != childAspectRatio ||
+        oldDelegate.mainAxisExtent != mainAxisExtent;
+    if (flag) layoutCache = null;
+    return flag;
+  }
+}