Hide viewport overlay when other windows are docked atop of the viewport

Changed the overlay from a separate top-level window to a child window
within the viewport. This ensures the overlay is properly occluded when
other windows are docked on top of the viewport. Otherwise, other windows
such the tranfer function editor would render behind the overlay.

Author: tarcila

tsd/src/tsd/ui/imgui/windows/Viewport.cpp

@@ -36,8 +36,6 @@ Viewport::Viewport(
     : Window(app, name)
 {
   setManipulator(m);
-  m_overlayWindowName = "overlay_";
-  m_overlayWindowName += name;
   setLibrary("");
 }
 
@@ -63,6 +61,8 @@ void Viewport::buildUI()
   updateImage();
   updateCamera();
 
+  ui_menubar();
+
   ImGui::BeginDisabled(!m_deviceReadyToUse);
 
   if (m_outputPass) {
@@ -72,15 +72,16 @@ void Viewport::buildUI()
         ImVec2(1, 0));
   }
 
-  if (m_showOverlay)
-    ui_overlay();
-
-  ImGui::EndDisabled();
-
   ui_gizmo();
   ui_handleInput();
   bool didPick = ui_picking(); // Needs to happen before ui_menubar
-  ui_menubar();
+
+  // Render the overlay after input handling so it does not interfere.
+  if (m_showOverlay) {
+    ui_overlay();
+  }
+
+  ImGui::EndDisabled();
 
   if (m_anariPass && !didPick) {
     bool needIDs = appCore()->getFirstSelected().valid()
@@ -1459,19 +1460,20 @@ bool Viewport::ui_picking()
 
 void Viewport::ui_overlay()
 {
-  ImGuiIO &io = ImGui::GetIO();
-  ImVec2 windowPos = ImGui::GetWindowPos();
-  windowPos.x += 10;
-  windowPos.y += 63 * io.FontGlobalScale;
+  ImVec2 contentStart = ImGui::GetCursorStartPos();
+  ImGui::SetCursorPos(ImVec2(contentStart[0] + 2.0f, contentStart[1] + 2.0f));
 
-  ImGuiWindowFlags window_flags = ImGuiWindowFlags_NoDecoration
-      | ImGuiWindowFlags_NoDocking | ImGuiWindowFlags_AlwaysAutoResize
-      | ImGuiWindowFlags_NoSavedSettings | ImGuiWindowFlags_NoFocusOnAppearing
-      | ImGuiWindowFlags_NoNav | ImGuiWindowFlags_NoMove;
+  ImGui::PushStyleColor(ImGuiCol_ChildBg, ImVec4(0.0f, 0.0f, 0.0f, 0.7f));
 
-  ImGui::SetNextWindowPos(windowPos, ImGuiCond_Always);
+  ImGuiChildFlags childFlags = ImGuiChildFlags_Border
+      | ImGuiChildFlags_AutoResizeX | ImGuiChildFlags_AutoResizeY;
+  ImGuiWindowFlags childWindowFlags =
+      ImGuiWindowFlags_NoScrollbar | ImGuiWindowFlags_NoScrollWithMouse;
 
-  if (ImGui::Begin(m_overlayWindowName.c_str(), nullptr, window_flags)) {
+  // Render overlay as a child window within the viewport.
+  // This ensures it's properly occluded when other windows are on top.
+  if (ImGui::BeginChild(
+          "##viewportOverlay", ImVec2(0, 0), childFlags, childWindowFlags)) {
     ImGui::Text("  device: %s", m_libName.c_str());
 
     // Camera indicator
@@ -1493,7 +1495,6 @@ void Viewport::ui_overlay()
     ImGui::Text("   (max): %.2fms", m_maxFL);
 
     ImGui::Separator();
-
     ImGui::Checkbox("camera config", &m_showCameraInfo);
     if (m_showCameraInfo) {
       auto at = m_arcball->at();
@@ -1516,9 +1517,10 @@ void Viewport::ui_overlay()
         m_arcball->setFixedDistance(fixedDist);
       }
     }
-
-    ImGui::End();
   }
+  ImGui::EndChild();
+
+  ImGui::PopStyleColor();
 }
 
 bool Viewport::canShowGizmo() const
@@ -1638,7 +1640,7 @@ void Viewport::ui_gizmo()
 
 int Viewport::windowFlags() const
 {
-  return ImGuiWindowFlags_MenuBar;
+  return ImGuiWindowFlags_MenuBar | ImGuiWindowFlags_NoScrollbar;
 }
 
 void Viewport::RendererUpdateDelegate::signalParameterUpdated(

tsd/src/tsd/ui/imgui/windows/Viewport.h

@@ -184,8 +184,6 @@ struct Viewport : public Window
   float m_latestAnariFL{0.f};
   float m_minFL{std::numeric_limits<float>::max()};
   float m_maxFL{-std::numeric_limits<float>::max()};
-
-  std::string m_overlayWindowName;
 };
 
 } // namespace tsd::ui::imgui