From 20c40020c088976cb4360b507ad3166aefd80197 Mon Sep 17 00:00:00 2001
From: Thibault Deckers <thibault.deckers@gmail.com>
Date: Tue, 9 Jun 2020 10:17:35 +0900
Subject: [PATCH] collection: sloppy scroll physics to improve scale gesture
 recognition

---
 lib/widgets/album/thumbnail_collection.dart   |  3 ++-
 lib/widgets/common/sloppy_scroll_physics.dart | 25 +++++++++++++++++++
 2 files changed, 27 insertions(+), 1 deletion(-)
 create mode 100644 lib/widgets/common/sloppy_scroll_physics.dart

diff --git a/lib/widgets/album/thumbnail_collection.dart b/lib/widgets/album/thumbnail_collection.dart
index b515d0af1..d300aa16d 100644
--- a/lib/widgets/album/thumbnail_collection.dart
+++ b/lib/widgets/album/thumbnail_collection.dart
@@ -12,6 +12,7 @@ import 'package:aves/widgets/album/grid/scaling.dart';
 import 'package:aves/widgets/album/grid/tile_extent_manager.dart';
 import 'package:aves/widgets/common/icons.dart';
 import 'package:aves/widgets/common/scroll_thumb.dart';
+import 'package:aves/widgets/common/sloppy_scroll_physics.dart';
 import 'package:draggable_scrollbar/draggable_scrollbar.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
@@ -153,7 +154,7 @@ class _CollectionScrollViewState extends State<CollectionScrollView> {
       primary: true,
       // workaround to prevent scrolling the app bar away
       // when there is no content and we use `SliverFillRemaining`
-      physics: collection.isEmpty ? const NeverScrollableScrollPhysics() : null,
+      physics: collection.isEmpty ? const NeverScrollableScrollPhysics() : const SloppyScrollPhysics(parent: AlwaysScrollableScrollPhysics()),
       cacheExtent: widget.cacheExtent,
       slivers: [
         appBar,
diff --git a/lib/widgets/common/sloppy_scroll_physics.dart b/lib/widgets/common/sloppy_scroll_physics.dart
new file mode 100644
index 000000000..1fbb8f158
--- /dev/null
+++ b/lib/widgets/common/sloppy_scroll_physics.dart
@@ -0,0 +1,25 @@
+import 'package:flutter/gestures.dart';
+import 'package:flutter/widgets.dart';
+
+class SloppyScrollPhysics extends ScrollPhysics {
+  const SloppyScrollPhysics({
+    this.touchSlopFactor = 1,
+    ScrollPhysics parent,
+  }) : super(parent: parent);
+
+  // in [0, 1]
+  // 0: most reactive but will not let other recognizers accept gestures
+  // 1: less reactive but gives the most leeway to other recognizers
+  final double touchSlopFactor;
+
+  @override
+  SloppyScrollPhysics applyTo(ScrollPhysics ancestor) {
+    return SloppyScrollPhysics(
+      touchSlopFactor: touchSlopFactor,
+      parent: buildParent(ancestor),
+    );
+  }
+
+  @override
+  double get dragStartDistanceMotionThreshold => kTouchSlop * touchSlopFactor;
+}