feat: Scrollbar auto collapse.

3 files changed, 43 insertions, 2 deletions

diff --git a/include/cru/platform/gui/UiApplication.hpp b/include/cru/platform/gui/UiApplication.hpp
index ba85020a..5a5b0b13 100644
--- a/include/cru/platform/gui/UiApplication.hpp
+++ b/include/cru/platform/gui/UiApplication.hpp
@@ -79,6 +79,9 @@ class TimerAutoCanceler {
   }
 
   TimerAutoCanceler& operator=(TimerAutoCanceler&& other) {
+    if (&other == this) {
+      return *this;
+    }
     Reset(other.id_);
     other.id_ = 0;
     return *this;
@@ -101,6 +104,8 @@ class TimerAutoCanceler {
     id_ = id;
   }
 
+  explicit operator bool() const { return id_; }
+
  private:
   long long id_;
 };
diff --git a/include/cru/ui/render/ScrollBar.hpp b/include/cru/ui/render/ScrollBar.hpp
index fc2910c4..7cfd2576 100644
--- a/include/cru/ui/render/ScrollBar.hpp
+++ b/include/cru/ui/render/ScrollBar.hpp
@@ -94,6 +94,11 @@ class ScrollBar : public Object {
   void SetCursor();
   void RestoreCursor();
 
+  void BeginAutoCollapseTimer();
+  void StopAutoCollapseTimer();
+
+  void OnMouseLeave();
+
  protected:
   gsl::not_null<ScrollRenderObject*> render_object_;
 
@@ -118,6 +123,8 @@ class ScrollBar : public Object {
   Event<Scroll> scroll_attempt_event_;
 
   std::optional<std::shared_ptr<platform::gui::ICursor>> old_cursor_;
+
+  platform::gui::TimerAutoCanceler auto_collapse_timer_canceler_;
 };
 
 class HorizontalScrollBar : public ScrollBar {
diff --git a/src/ui/render/ScrollBar.cpp b/src/ui/render/ScrollBar.cpp
index ee4b9e0d..02e079e9 100644
--- a/src/ui/render/ScrollBar.cpp
+++ b/src/ui/render/ScrollBar.cpp
@@ -14,14 +14,17 @@
 
 #include <algorithm>
 #include <cassert>
+#include <chrono>
 #include <gsl/pointers>
 #include <optional>
 #include <stdexcept>
 
 namespace cru::ui::render {
+using namespace std::chrono_literals;
 constexpr float kScrollBarCollapseThumbWidth = 2;
 constexpr float kScrollBarCollapsedTriggerExpandAreaWidth = 5;
 constexpr float kScrollBarExpandWidth = 10;
+constexpr auto kScrollBarAutoCollapseDelay = 1500ms;
 
 constexpr std::array<ScrollBarAreaKind, 5> kScrollBarAreaKindList{
     ScrollBarAreaKind::UpArrow, ScrollBarAreaKind::DownArrow,
@@ -131,6 +134,13 @@ void ScrollBar::InstallHandlers(controls::Control* control) {
               if (event.GetButton() == mouse_buttons::left &&
                   move_thumb_start_) {
                 move_thumb_start_ = std::nullopt;
+
+                auto hit_test_result =
+                    ExpandedHitTest(event.GetPoint(this->render_object_));
+                if (!hit_test_result) {
+                  OnMouseLeave();
+                }
+
                 control->ReleaseMouse();
                 event.SetHandled();
                 return true;
@@ -159,8 +169,9 @@ void ScrollBar::InstallHandlers(controls::Control* control) {
                       ExpandedHitTest(event.GetPoint(this->render_object_));
                   if (hit_test_result) {
                     SetCursor();
+                    StopAutoCollapseTimer();
                   } else {
-                    RestoreCursor();
+                    OnMouseLeave();
                   }
                 } else {
                   auto trigger_expand_area =
@@ -182,7 +193,9 @@ void ScrollBar::InstallHandlers(controls::Control* control) {
     event_guard_ +=
         control->MouseLeaveEvent()->Bubble()->PrependShortCircuitHandler(
             [this](event::MouseEventArgs&) {
-              if (IsExpanded() && !move_thumb_start_) RestoreCursor();
+              if (IsExpanded() && !move_thumb_start_) {
+                OnMouseLeave();
+              }
               return false;
             });
   }
@@ -267,6 +280,22 @@ void ScrollBar::RestoreCursor() {
   }
 }
 
+void ScrollBar::BeginAutoCollapseTimer() {
+  if (!auto_collapse_timer_canceler_ && IsExpanded()) {
+    auto_collapse_timer_canceler_ = GetUiApplication()->SetTimeout(
+        kScrollBarAutoCollapseDelay, [this] { this->SetExpanded(false); });
+  }
+}
+
+void ScrollBar::StopAutoCollapseTimer() {
+  auto_collapse_timer_canceler_.Reset();
+}
+
+void ScrollBar::OnMouseLeave() {
+  RestoreCursor();
+  BeginAutoCollapseTimer();
+}
+
 std::optional<ScrollBarAreaKind> ScrollBar::ExpandedHitTest(
     const Point& point) {
   for (auto kind : kScrollBarAreaKindList) {