PaintBrush: Switch the active layer when clicking one with move tool

This feels very intuitive and nice, although maybe we need some way to
override this behavior for the scenario where you're intending to move
something currently behind something else.

Applications/PaintBrush/ImageEditor.cpp

@@ -85,8 +85,18 @@ static GUI::MouseEvent event_adjusted_for_layer(const GUI::MouseEvent& original_
 
 void ImageEditor::mousedown_event(GUI::MouseEvent& event)
 {
-    if (!m_active_layer || !m_active_tool)
+    if (!m_active_tool)
         return;
+
+    if (m_active_tool->is_move_tool()) {
+        if (auto* other_layer = layer_at(event.position())) {
+            set_active_layer(other_layer);
+        }
+    }
+
+    if (!m_active_layer)
+        return;
+
     auto layer_event = event_adjusted_for_layer(event, *m_active_layer);
     m_active_tool->on_mousedown(*m_active_layer, layer_event, event);
 }
@@ -124,7 +134,21 @@ void ImageEditor::set_active_layer(Layer* layer)
     if (m_active_layer == layer)
         return;
     m_active_layer = layer;
-    update();
+
+    if (m_active_layer) {
+        size_t index = 0;
+        for (; index < m_image->layer_count(); ++index) {
+            if (&m_image->layer(index) == layer)
+                break;
+        }
+        if (on_active_layer_change)
+            on_active_layer_change(m_image->layer_model().index(index));
+    } else {
+        if (on_active_layer_change)
+            on_active_layer_change({});
+    }
+
+    layers_did_change();
 }
 
 void ImageEditor::set_active_tool(Tool* tool)
@@ -183,4 +207,16 @@ void ImageEditor::set_secondary_color(Color color)
         on_secondary_color_change(color);
 }
 
+Layer* ImageEditor::layer_at(const Gfx::Point& position)
+{
+    if (!m_image)
+        return nullptr;
+    for (ssize_t i = m_image->layer_count() - 1; i >= 0; --i) {
+        auto& layer = m_image->layer(i);
+        if (layer.relative_rect().contains(position))
+            return const_cast<Layer*>(&layer);
+    }
+    return nullptr;
+}
+
 }

Applications/PaintBrush/ImageEditor.h

@@ -51,6 +51,8 @@ public:
 
     void layers_did_change();
 
+    Layer* layer_at(const Gfx::Point&);
+
     Color primary_color() const { return m_primary_color; }
     void set_primary_color(Color);
 
@@ -63,6 +65,8 @@ public:
     Function<void(Color)> on_primary_color_change;
     Function<void(Color)> on_secondary_color_change;
 
+    Function<void(const GUI::ModelIndex&)> on_active_layer_change;
+
 private:
     ImageEditor();
 

Applications/PaintBrush/MoveTool.h

@@ -42,6 +42,7 @@ public:
 
 private:
     virtual const char* class_name() const override { return "MoveTool"; }
+    virtual bool is_move_tool() const override { return true; }
 
     RefPtr<Layer> m_layer_being_moved;
     Gfx::Point m_event_origin;

Applications/PaintBrush/Tool.h

@@ -48,6 +48,8 @@ public:
     virtual void on_keydown(GUI::KeyEvent&) {}
     virtual void on_keyup(GUI::KeyEvent&) {}
 
+    virtual bool is_move_tool() const { return false; }
+
     void clear() { m_editor = nullptr; }
     void setup(ImageEditor&);
 

Applications/PaintBrush/main.cpp

@@ -158,6 +158,13 @@ int main(int argc, char** argv)
 
     app.set_menubar(move(menubar));
 
+    image_editor.on_active_layer_change = [&](auto& index) {
+        if (index.is_valid())
+            layer_table_view.selection().set(index);
+        else
+            layer_table_view.selection().clear();
+    };
+
     auto image = PaintBrush::Image::create_with_size({ 640, 480 });
 
     auto bg_layer = PaintBrush::Layer::create_with_size({ 640, 480 }, "Background");