Fix ImGui input processing

PiperOrigin-RevId: 808555760
Change-Id: Ie443143d9c058058b99786e44f27715b05c9f8ed

src/experimental/toolbox/window.cc

@@ -130,7 +130,7 @@ std::string Window::GetDropFile() {
   return tmp;
 }
 
-Window::Status Window::ProcessEvents() {
+Window::Status Window::NewFrame() {
   SDL_Event event;
   while (SDL_PollEvent(&event)) {
     ImGui_ImplSDL2_ProcessEvent(&event);
@@ -158,6 +158,15 @@ Window::Status Window::ProcessEvents() {
   return should_exit_ ? kQuitting : kRunning;
 }
 
+void Window::EndFrame() {
+  // We use ImGui for input management in addition to GUI rendering so its
+  // important to call ImGui::EndFrame even if we don't call ImGui::Render.
+  // Note ImGui::Render internally calls ImGui::EndFrame, but so long as
+  // ImGui::NewFrame has been called, ImGui::EndFrame may be called multiple
+  // times; it will be a no-op.
+  ImGui::EndFrame();
+}
+
 void Window::Present() {
   // Filament (with the exception of WebGL) handles the swapchain internally.
   if (config_ != kFilamentVulkan && config_ != kFilamentOpenGL) {

src/experimental/toolbox/window.h

@@ -50,8 +50,12 @@ class Window {
     kQuitting,
   };
 
-  // Processes all pendings window events, returning the status of the window.
-  Status ProcessEvents();
+  // Processes all pendings window events and prepares ImGui for input handling
+  // and GUI rendering. Returns the status of the window.
+  Status NewFrame();
+
+  // Finalizes ImGui input handling. Must call NewFrame first.
+  void EndFrame();
 
   // Swaps and presents the window buffer.
   void Present();