WindowServer+LibGUI: Add a "drag move" event

This allows windows/widgets to learn when something is being dragged
over them. They can then repaint themselves somehow to indicate that
they are willing to accept a drop.

Currently this is piggybacking somewhat on the mouse event mechanism
in WindowServer. I'm not sure that's the best design but it seemed
easier to do it this way right now.

9 files changed, 71 insertions, 8 deletions

diff --git a/Libraries/LibGUI/Event.h b/Libraries/LibGUI/Event.h
index 7b6b472176..c518a694a1 100644
--- a/Libraries/LibGUI/Event.h
+++ b/Libraries/LibGUI/Event.h
@@ -60,6 +60,7 @@ public:
         WindowCloseRequest,
         ContextMenu,
         EnabledChange,
+        DragMove,
         Drop,
 
         __Begin_WM_Events,
@@ -306,6 +307,23 @@ private:
     int m_wheel_delta { 0 };
 };
 
+class DragEvent final : public Event {
+public:
+    DragEvent(Type type, const Gfx::Point& position, const String& data_type)
+        : Event(type)
+        , m_position(position)
+        , m_data_type(data_type)
+    {
+    }
+
+    const Gfx::Point& position() const { return m_position; }
+    const String& data_type() const { return m_data_type; }
+
+private:
+    Gfx::Point m_position;
+    String m_data_type;
+};
+
 class DropEvent final : public Event {
 public:
     DropEvent(const Gfx::Point& position, const String& text, const String& data_type, const String& data)
diff --git a/Libraries/LibGUI/Widget.cpp b/Libraries/LibGUI/Widget.cpp
index b4b2ccc084..0997b52773 100644
--- a/Libraries/LibGUI/Widget.cpp
+++ b/Libraries/LibGUI/Widget.cpp
@@ -26,8 +26,6 @@
 
 #include <AK/Assertions.h>
 #include <AK/JsonObject.h>
-#include <LibGfx/Bitmap.h>
-#include <LibGfx/Palette.h>
 #include <LibGUI/Action.h>
 #include <LibGUI/Application.h>
 #include <LibGUI/Button.h>
@@ -46,6 +44,8 @@
 #include <LibGUI/Widget.h>
 #include <LibGUI/Window.h>
 #include <LibGUI/WindowServerConnection.h>
+#include <LibGfx/Bitmap.h>
+#include <LibGfx/Palette.h>
 #include <unistd.h>
 
 namespace GUI {
@@ -182,6 +182,8 @@ void Widget::event(Core::Event& event)
         return handle_mouseup_event(static_cast<MouseEvent&>(event));
     case Event::MouseWheel:
         return mousewheel_event(static_cast<MouseEvent&>(event));
+    case Event::DragMove:
+        return drag_move_event(static_cast<DragEvent&>(event));
     case Event::Drop:
         return drop_event(static_cast<DropEvent&>(event));
     case Event::Enter:
@@ -379,6 +381,12 @@ void Widget::change_event(Event&)
 {
 }
 
+void Widget::drag_move_event(DragEvent& event)
+{
+    dbg() << class_name() << "{" << this << "} DRAG MOVE  position: " << event.position() << ", data_type: '" << event.data_type() << "'";
+    event.ignore();
+}
+
 void Widget::drop_event(DropEvent& event)
 {
     dbg() << class_name() << "{" << this << "} DROP  position: " << event.position() << ", text: '" << event.text() << "'";
diff --git a/Libraries/LibGUI/Widget.h b/Libraries/LibGUI/Widget.h
index 9ecb8fe8c1..d294673dca 100644
--- a/Libraries/LibGUI/Widget.h
+++ b/Libraries/LibGUI/Widget.h
@@ -303,6 +303,7 @@ protected:
     virtual void leave_event(Core::Event&);
     virtual void child_event(Core::ChildEvent&) override;
     virtual void change_event(Event&);
+    virtual void drag_move_event(DragEvent&);
     virtual void drop_event(DropEvent&);
 
 private:
diff --git a/Libraries/LibGUI/Window.cpp b/Libraries/LibGUI/Window.cpp
index c93e9d00e8..a0b5dc87c2 100644
--- a/Libraries/LibGUI/Window.cpp
+++ b/Libraries/LibGUI/Window.cpp
@@ -319,6 +319,16 @@ void Window::event(Core::Event& event)
     if (event.type() > Event::__Begin_WM_Events && event.type() < Event::__End_WM_Events)
         return wm_event(static_cast<WMEvent&>(event));
 
+    if (event.type() == Event::DragMove) {
+        if (!m_main_widget)
+            return;
+        auto& drag_event = static_cast<DragEvent&>(event);
+        auto result = m_main_widget->hit_test(drag_event.position());
+        auto local_event = make<DragEvent>(static_cast<Event::Type>(drag_event.type()), result.local_position, drag_event.data_type());
+        ASSERT(result.widget);
+        return result.widget->dispatch_event(*local_event, this);
+    }
+
     Core::Object::event(event);
 }
 
diff --git a/Libraries/LibGUI/WindowServerConnection.cpp b/Libraries/LibGUI/WindowServerConnection.cpp
index 3ea6a6a572..bfcc000f2e 100644
--- a/Libraries/LibGUI/WindowServerConnection.cpp
+++ b/Libraries/LibGUI/WindowServerConnection.cpp
@@ -24,8 +24,6 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
-#include <LibGfx/Palette.h>
-#include <LibGfx/SystemTheme.h>
 #include <LibGUI/Action.h>
 #include <LibGUI/Application.h>
 #include <LibGUI/Clipboard.h>
@@ -36,6 +34,8 @@
 #include <LibGUI/Widget.h>
 #include <LibGUI/Window.h>
 #include <LibGUI/WindowServerConnection.h>
+#include <LibGfx/Palette.h>
+#include <LibGfx/SystemTheme.h>
 
 //#define GEVENTLOOP_DEBUG
 
@@ -217,8 +217,12 @@ void WindowServerConnection::handle(const Messages::WindowClient::MouseMove& mes
     dbgprintf("WID=%d MouseMove %d,%d,%d\n", message.window_id(), message.mouse_position().x(), message.mouse_position().y(), message.wheel_delta();
 #endif
 
-    if (auto* window = Window::from_window_id(message.window_id()))
-        Core::EventLoop::current().post_event(*window, make<MouseEvent>(Event::MouseMove, message.mouse_position(), message.buttons(), to_gmousebutton(message.button()), message.modifiers(), message.wheel_delta()));
+    if (auto* window = Window::from_window_id(message.window_id())) {
+        if (message.is_drag())
+            Core::EventLoop::current().post_event(*window, make<DragEvent>(Event::DragMove, message.mouse_position(), message.drag_data_type()));
+        else
+            Core::EventLoop::current().post_event(*window, make<MouseEvent>(Event::MouseMove, message.mouse_position(), message.buttons(), to_gmousebutton(message.button()), message.modifiers(), message.wheel_delta()));
+    }
 }
 
 void WindowServerConnection::handle(const Messages::WindowClient::MouseDoubleClick& message)
diff --git a/Servers/WindowServer/Event.h b/Servers/WindowServer/Event.h
index 8b7bd97d13..781f2df903 100644
--- a/Servers/WindowServer/Event.h
+++ b/Servers/WindowServer/Event.h
@@ -117,6 +117,11 @@ public:
     unsigned buttons() const { return m_buttons; }
     unsigned modifiers() const { return m_modifiers; }
     int wheel_delta() const { return m_wheel_delta; }
+    bool is_drag() const { return m_drag; }
+    const String& drag_data_type() const { return m_drag_data_type; }
+
+    void set_drag(bool b) { m_drag = b; }
+    void set_drag_data_type(const String& drag_data_type) { m_drag_data_type = drag_data_type; }
 
     MouseEvent translated(const Gfx::Point& delta) const { return MouseEvent((Type)type(), m_position.translated(delta), m_buttons, m_button, m_modifiers, m_wheel_delta); }
 
@@ -126,6 +131,8 @@ private:
     MouseButton m_button { MouseButton::None };
     unsigned m_modifiers { 0 };
     int m_wheel_delta { 0 };
+    bool m_drag { false };
+    String m_drag_data_type;
 };
 
 class ResizeEvent final : public Event {
diff --git a/Servers/WindowServer/Window.cpp b/Servers/WindowServer/Window.cpp
index a25cc5aa0c..a322d72cdd 100644
--- a/Servers/WindowServer/Window.cpp
+++ b/Servers/WindowServer/Window.cpp
@@ -114,7 +114,7 @@ void Window::handle_mouse_event(const MouseEvent& event)
 
     switch (event.type()) {
     case Event::MouseMove:
-        m_client->post_message(Messages::WindowClient::MouseMove(m_window_id, event.position(), (u32)event.button(), event.buttons(), event.modifiers(), event.wheel_delta()));
+        m_client->post_message(Messages::WindowClient::MouseMove(m_window_id, event.position(), (u32)event.button(), event.buttons(), event.modifiers(), event.wheel_delta(), event.is_drag(), event.drag_data_type()));
         break;
     case Event::MouseDown:
         m_client->post_message(Messages::WindowClient::MouseDown(m_window_id, event.position(), (u32)event.button(), event.buttons(), event.modifiers(), event.wheel_delta()));
diff --git a/Servers/WindowServer/WindowClient.ipc b/Servers/WindowServer/WindowClient.ipc
index e1b8e8398a..4e3c077a7d 100644
--- a/Servers/WindowServer/WindowClient.ipc
+++ b/Servers/WindowServer/WindowClient.ipc
@@ -1,7 +1,7 @@
 endpoint WindowClient = 4
 {
     Paint(i32 window_id, Gfx::Size window_size, Vector<Gfx::Rect> rects) =|
-    MouseMove(i32 window_id, Gfx::Point mouse_position, u32 button, u32 buttons, u32 modifiers, i32 wheel_delta) =|
+    MouseMove(i32 window_id, Gfx::Point mouse_position, u32 button, u32 buttons, u32 modifiers, i32 wheel_delta, bool is_drag, String drag_data_type) =|
     MouseDown(i32 window_id, Gfx::Point mouse_position, u32 button, u32 buttons, u32 modifiers, i32 wheel_delta) =|
     MouseDoubleClick(i32 window_id, Gfx::Point mouse_position, u32 button, u32 buttons, u32 modifiers, i32 wheel_delta) =|
     MouseUp(i32 window_id, Gfx::Point mouse_position, u32 button, u32 buttons, u32 modifiers, i32 wheel_delta) =|
diff --git a/Servers/WindowServer/WindowManager.cpp b/Servers/WindowServer/WindowManager.cpp
index 2a7d7383b1..689cb5734c 100644
--- a/Servers/WindowServer/WindowManager.cpp
+++ b/Servers/WindowServer/WindowManager.cpp
@@ -594,6 +594,21 @@ bool WindowManager::process_ongoing_drag(MouseEvent& event, Window*& hovered_win
 {
     if (!m_dnd_client)
         return false;
+
+    if (event.type() == Event::MouseMove) {
+        // We didn't let go of the drag yet, see if we should send some drag move events..
+        for_each_visible_window_from_front_to_back([&](Window& window) {
+            if (!window.rect().contains(event.position()))
+                return IterationDecision::Continue;
+            hovered_window = &window;
+            auto translated_event = event.translated(-window.position());
+            translated_event.set_drag(true);
+            translated_event.set_drag_data_type(m_dnd_data_type);
+            deliver_mouse_event(window, translated_event);
+            return IterationDecision::Break;
+        });
+    }
+
     if (!(event.type() == Event::MouseUp && event.button() == MouseButton::Left))
         return true;