implement brush preset import

src/node_panel_brush.cpp

@@ -463,6 +463,24 @@ void NodePanelBrushPreset::init()
         root()->update();
         auto bounds = root()->GetSize() - zw(popup->get_children_rect());
         popup->SetPosition(glm::clamp(popup->m_pos, { 0, 0 }, bounds));
+        popup->on_select = [this, popup] (Node* target, int index) {
+            switch (index)
+            {
+                case 0: // download
+                    break;
+                case 1: // import
+                    App::I->pick_file({".abr", ".ABR"}, [] (std::string path) {
+                        std::thread([path] {
+                            BT_SetTerminate();
+                            App::I->stroke->import_abr(path);
+                        }).detach();
+                    });
+                    break;
+                case 2: // export
+                    break;
+            }
+            popup->destroy();
+        };
     };
 
     if (Asset::exist(App::I->data_path + "/settings/presets.bin") && !restore())