support a proper shutdown flow (#311)

Author: nmwsharp

examples/demo-app/demo_app.cpp

@@ -880,6 +880,7 @@ int main(int argc, char** argv) {
   // }
 
   std::cout << "!!!! shutdown time" << std::endl;
+  polyscope::shutdown();
 
   return 0;
 }

include/polyscope/messages.h

@@ -27,4 +27,5 @@ void exception(std::string message);
 
 // Process any warnings that have accumulated, showing them to the user and clearing the queue.
 void showDelayedWarnings();
+void clearMessages();
 } // namespace polyscope

include/polyscope/polyscope.h

@@ -60,7 +60,7 @@ void unshow();
 void frameTick();
 
 // Do shutdown work and de-initialize Polyscope
-void shutdown();
+void shutdown(bool allowMidFrameShutdown=false);
 
 // Returns true if the user has tried to exit the window at the OS level, e.g clicking the close button. Useful for
 // deciding when to exit your control loop when using frameTick()

include/polyscope/render/engine.h

@@ -442,6 +442,7 @@ class Engine {
   virtual ~Engine();
 
   // High-level control
+  virtual void shutdown() {};
   virtual void checkError(bool fatal = false) = 0;
   void buildEngineGui();
 

include/polyscope/render/mock_opengl/mock_gl_engine.h

@@ -325,6 +325,7 @@ class MockGLEngine : public Engine {
 
   // High-level control
   void initialize();
+  virtual void shutdown() override;
   void checkError(bool fatal = false) override;
 
   void swapDisplayBuffers() override;

include/polyscope/render/opengl/gl_engine_egl.h

@@ -38,6 +38,7 @@ class GLEngineEGL : public GLEngine {
 
   // High-level control
   void initialize();
+  virtual void shutdown() override;
   void swapDisplayBuffers() override;
   void checkError(bool fatal = false) override;
 

include/polyscope/render/opengl/gl_engine_glfw.h

@@ -48,6 +48,7 @@ class GLEngineGLFW : public GLEngine {
 
   // High-level control
   void initialize();
+  virtual void shutdown() override;
   void swapDisplayBuffers() override;
 
   // === Windowing and framework things

include/polyscope/slice_plane.h

@@ -111,6 +111,7 @@ class SlicePlane {
 
 SlicePlane* addSceneSlicePlane(bool initiallyVisible = false);
 void removeLastSceneSlicePlane();
+void removeAllSlicePlanes();
 void buildSlicePlaneGUI();
 
 // flag to open the slice plane menu after adding a slice plane

src/messages.cpp

@@ -235,7 +235,7 @@ void terminatingError(std::string message) {
   pushContext(func, false);
 
   // Quit the program
-  shutdown();
+  shutdown(true);
   std::exit(-1);
 }
 
@@ -281,4 +281,6 @@ void showDelayedWarnings() {
   }
 }
 
+void clearMessages() { warningMessages.clear(); }
+
 } // namespace polyscope

src/polyscope.cpp

@@ -934,14 +934,30 @@ bool windowRequestsClose() {
   return false;
 }
 
-void shutdown() {
+void shutdown(bool allowMidFrameShutdown) {
+
+  if (!allowMidFrameShutdown && contextStack.size() > 1) {
+    terminatingError("shutdown() was called mid-frame (e.g. in a per-frame callback, or UI element). This is not "
+                     "permitted, shutdown() may only be called when the main loop is not executing.");
+  }
 
-  // TODO should we make an effort to destruct everything here?
   if (options::usePrefsFile) {
     writePrefsFile();
   }
 
-  render::engine->shutdownImGui();
+  // Clear out all structures and other scene objects
+  removeAllStructures();
+  removeAllGroups();
+  removeAllSlicePlanes();
+  clearMessages();
+  state::userCallback = nullptr;
+
+  // Shut down the render engine
+  render::engine->shutdown();
+  delete render::engine;
+  render::engine = nullptr;
+  state::backend = "";
+  state::initialized = false;
 }
 
 bool registerStructure(Structure* s, bool replaceIfPresent) {