add duplicate layer

src/app_layout.cpp

@@ -170,6 +170,25 @@ void App::init_sidebar()
         title_update();
     };
 
+    layers->on_layer_duplicate = [this](Node*, int source_index) {
+        Canvas::I->layer_add(layers->m_layers.back()->m_label_text.c_str());
+        auto& dst = Canvas::I->m_layers.back();
+        auto& src = Canvas::I->m_layers[Canvas::I->m_order[source_index]];
+        for (int i = 0; i < 6; i++)
+        {
+            if (!src.m_dirty_face[i])
+                continue;
+            dst.m_rtt[i].copy(src.m_rtt[i]);
+            dst.m_dirty_face[i] = src.m_dirty_face[i];
+            dst.m_dirty_box[i] = src.m_dirty_box[i];
+            dst.m_opacity = src.m_opacity;
+            dst.m_blend_mode = src.m_blend_mode;
+            dst.m_alpha_locked = src.m_alpha_locked;
+        }
+        Canvas::I->m_unsaved = true;
+        title_update();
+    };
+
     layers->on_layer_change = [this](Node*, int old_idx, int new_idx) {
         canvas->m_canvas->m_current_layer_idx = canvas->m_canvas->m_order[new_idx];
     };