cabana: make the Signals pane a native dock panel, fix pad (#38889)

* cabana: align center tabs and keep signal panel docked

* cabana: prevent panels from docking into the tabless center

* cabana: use native docking for the Signals panel

* cabana: migrate dock tabs when loading the layout

openpilot/tools/cabana/ui/inistate.cc

@@ -107,6 +107,15 @@ std::string migrateQtState() {
   return std::string(buf.c_str());
 }
 
+void migrateDockLayout() {
+  // Show dock tabs hidden by older layouts.
+  if (const auto *center = ImGui::FindWindowSettingsByID(ImHashStr("###CenterWidget"))) {
+    if (auto *node = ImGui::DockBuilderGetNode(center->DockId)) {
+      node->LocalFlags &= ~ImGuiDockNodeFlags_NoTabBar;
+    }
+  }
+}
+
 }  // namespace
 
 void addSettingsHandler() {
@@ -123,6 +132,8 @@ void load() {
   if (settings.ui_state.empty()) settings.ui_state = migrateQtState();
   if (!settings.ui_state.empty())
     ImGui::LoadIniSettingsFromMemory(settings.ui_state.data(), settings.ui_state.size());
+
+  migrateDockLayout();
 }
 
 void applyWindowGeometry(GLFWwindow *window) {

openpilot/tools/cabana/ui/mainwin.cc

@@ -31,7 +31,7 @@
 namespace {
 // dock window ids (the visible titles change, the part after ### is the identity)
 constexpr const char *VIDEO_PANEL = "###VideoPanel";
-constexpr const char *CENTER_PANEL = "###CenterWidget";
+constexpr const char *CENTER_PANEL = "Signals###CenterWidget";
 constexpr const char *CHARTS_WINDOW = "Charts###ChartsWindow";
 }  // namespace
 
@@ -777,8 +777,6 @@ void MainWindow::drawDockspace() {
   // the status bar sits below the dockspace: reserve its height plus the item spacing between the two,
   // otherwise the host window is a few pixels taller than the viewport and scrolls
   const float status_height = full_screen_ ? 0.0f : ImGui::GetFrameHeight() + ImGui::GetStyle().ItemSpacing.y;
-  const float top_gap = full_screen_ ? 0.0f : ImGui::GetStyle().ItemSpacing.y;
-  ImGui::SetCursorPosY(ImGui::GetCursorPosY() + top_gap);
   const ImVec2 dock_size(ImGui::GetContentRegionAvail().x, ImGui::GetContentRegionAvail().y - status_height);
   const ImGuiID dock_id = ImGui::GetID("cabana_dockspace");
   if (reset_layout_ || ImGui::DockBuilderGetNode(dock_id) == nullptr ||
@@ -796,7 +794,6 @@ void MainWindow::drawDockspace() {
     ImGui::DockBuilderDockWindow(MESSAGES_PANEL_ID, left);
     ImGui::DockBuilderDockWindow(VIDEO_PANEL, right);
     ImGui::DockBuilderDockWindow(CENTER_PANEL, center);
-    ImGui::DockBuilderGetNode(center)->LocalFlags |= ImGuiDockNodeFlags_NoTabBar;
     ImGui::DockBuilderFinish(dock_id);
     reset_layout_ = false;
   }
@@ -879,13 +876,12 @@ void MainWindow::draw() {
   drawDockspace();
 
   // the central widget has no scrollbars of its own (the views inside scroll)
+  setNextPanelClass();
   if (beginPanel(CENTER_PANEL, nullptr, ImGuiWindowFlags_NoScrollbar | ImGuiWindowFlags_NoScrollWithMouse)) {
-    ImGui::BeginChild("center", ImVec2(0, 0), ImGuiChildFlags_Borders, ImGuiWindowFlags_NoScrollbar | ImGuiWindowFlags_NoScrollWithMouse);
     center_widget_.draw();
     if (auto *detail = center_widget_.getDetailWidget(); detail && help_overlay_.visible()) {
       for (const auto &[text, rect] : detail->helpRects()) help_overlay_.add(text, rect);
     }
-    ImGui::EndChild();
   }
   ImGui::End();
   // Submit the same dock windows while loading, so ImGui doesn't collapse their

openpilot/tools/cabana/ui/widgets/detailwidget.cc

@@ -280,6 +280,8 @@ void DetailWidget::drawTabWidget() {
 
 void DetailWidget::draw() {
   tabbar_.draw();
+  ImGui::BeginChild("message_content", ImVec2(0, 0), ImGuiChildFlags_Borders,
+                    ImGuiWindowFlags_NoScrollbar | ImGuiWindowFlags_NoScrollWithMouse);
   drawToolBar();
 
   if (warning_widget_visible_) {
@@ -289,6 +291,7 @@ void DetailWidget::draw() {
   }
 
   drawTabWidget();
+  ImGui::EndChild();
 
   if (edit_dlg_ && !edit_dlg_->draw()) {
     if (edit_dlg_->accepted()) {