WindowServer: Flash modal window when clicking on window blocked by it

This makes window modality a bit more discoverable by indicating to the
user that the modal window must be closed before mouse interaction is
possible in the clicked window.

Services/WindowServer/WindowFrame.cpp

@@ -160,6 +160,10 @@ Gfx::IntRect WindowFrame::title_bar_text_rect() const
 Gfx::WindowTheme::WindowState WindowFrame::window_state_for_theme() const
 {
     auto& wm = WindowManager::the();
+
+    if (m_flash_timer && m_flash_timer->is_active())
+        return m_flash_counter & 1 ? Gfx::WindowTheme::WindowState::Active : Gfx::WindowTheme::WindowState::Inactive;
+
     if (&m_window == wm.m_highlight_window)
         return Gfx::WindowTheme::WindowState::Highlighted;
     if (&m_window == wm.m_move_window)
@@ -360,4 +364,19 @@ void WindowFrame::on_mouse_event(const MouseEvent& event)
     if (m_window.is_resizable() && event.type() == Event::MouseDown && event.button() == MouseButton::Left)
         wm.start_window_resize(m_window, event.translated(rect().location()));
 }
+
+void WindowFrame::start_flash_animation()
+{
+    if (!m_flash_timer) {
+        m_flash_timer = Core::Timer::construct(100, [this] {
+            ASSERT(m_flash_counter);
+            invalidate_title_bar();
+            if (!--m_flash_counter)
+                m_flash_timer->stop();
+        });
+    }
+    m_flash_counter = 8;
+    m_flash_timer->start();
+}
+
 }

Services/WindowServer/WindowFrame.h

@@ -28,6 +28,8 @@
 
 #include <AK/Forward.h>
 #include <AK/NonnullOwnPtrVector.h>
+#include <AK/RefPtr.h>
+#include <LibCore/Forward.h>
 #include <LibGfx/Forward.h>
 #include <LibGfx/WindowTheme.h>
 
@@ -58,6 +60,8 @@ public:
     void layout_buttons();
     void set_button_icons();
 
+    void start_flash_animation();
+
 private:
     void paint_notification_frame(Gfx::Painter&);
     void paint_normal_frame(Gfx::Painter&);
@@ -69,6 +73,9 @@ private:
     Button* m_close_button { nullptr };
     Button* m_maximize_button { nullptr };
     Button* m_minimize_button { nullptr };
+
+    RefPtr<Core::Timer> m_flash_timer;
+    size_t m_flash_counter { 0 };
 };
 
 }

Services/WindowServer/WindowManager.cpp

@@ -996,6 +996,11 @@ void WindowManager::process_mouse_event(MouseEvent& event, Window*& hovered_wind
             // Well okay, let's see if we're hitting the frame or the window inside the frame.
             if (window.rect().contains(event.position())) {
                 if (event.type() == Event::MouseDown) {
+                    // We're clicking on something that's blocked by a modal window.
+                    // Flash the modal window to let the user know about it.
+                    if (auto* blocking_modal_window = window.is_blocked_by_modal_window())
+                        blocking_modal_window->frame().start_flash_animation();
+
                     if (window.type() == WindowType::Normal)
                         move_to_front_and_make_active(window);
                     else if (window.type() == WindowType::Desktop)