allow gui::Window to execute the passed lambda right before ImGui::Begin()

common/gui_window.hh

@@ -25,12 +25,14 @@ class Window {
   Window& operator=(const Window&) = delete;
   Window& operator=(Window&&) = delete;
 
-  bool Begin() noexcept {
+  bool Begin(const std::function<void()>& before = {}) noexcept {
     if (std::exchange(set_focus_, false)) {
       ImGui::SetNextWindowFocus();
       shown_ = true;
     }
     if (!shown_) return false;
+
+    before();
     need_end_ = true;
     return ImGui::Begin(id().c_str(), &shown_);
   }

file/system_dir.cc

@@ -205,9 +205,11 @@ void Dir::Update() noexcept {
   }
 
   // tree view window
+  const auto kInit = [em]() {
+    ImGui::SetNextWindowSize({8*em, 8*em}, ImGuiCond_FirstUseEver);
+  };
   const char* popup = nullptr;
-  ImGui::SetNextWindowSize({8*em, 8*em}, ImGuiCond_FirstUseEver);
-  if (win_.Begin()) {
+  if (win_.Begin(kInit)) {
     if (ImGui::BeginPopupContextWindow()) {
       if (ImGui::MenuItem("new")) {
         popup = "NewItemPopup";

file/system_logger.cc

@@ -146,6 +146,8 @@ void Logger::Update() noexcept {
     ImGui::OpenPopup(name);
   }
 
+  const auto em = ImGui::GetFontSize();
+
   // config popup
   if (ImGui::BeginPopup("ConfigPopup")) {
     ImGui::TextUnformatted("System/Logger Config");
@@ -172,7 +174,10 @@ void Logger::Update() noexcept {
   }
 
   // LogView
-  if (win_.Begin()) {
+  const auto kInit = [em]() {
+    ImGui::SetNextWindowSize({48*em, 16*em}, ImGuiCond_FirstUseEver);
+  };
+  if (win_.Begin(kInit)) {
     constexpr auto kTableFlags =
         ImGuiTableFlags_Resizable         |
         ImGuiTableFlags_Hideable          |