Make it possible to hide the main window

ksp_plugin_adapter/flight_planner.cs

@@ -5,7 +5,7 @@
 namespace principia {
 namespace ksp_plugin_adapter {
 
-class FlightPlanner : VesselSupervisedWindowRenderer {
+class FlightPlanner : RequiredVesselSupervisedWindowRenderer {
   public FlightPlanner(PrincipiaPluginAdapter adapter,
                        PredictedVessel predicted_vessel) : base(
       adapter,

ksp_plugin_adapter/ksp_plugin_adapter.cs

@@ -975,9 +975,10 @@ private void OnGUI() {
 
     if (hide_all_gui_ || !in_principia_scene_) {
       LockClearing();
-    } else if (main_window_.Shown()) {
+    } else if (WindowsRendering.GetInvocationList().Length > 0) {
       WindowsRendering();
     } else {
+      // There are no windows to render.
       LockClearing();
     }
   }

ksp_plugin_adapter/orbit_analyser.cs

@@ -155,7 +155,7 @@ public static bool TryParseMissionDuration(string str, out double seconds) {
   }
 }
 
-internal abstract class OrbitAnalyser : VesselSupervisedWindowRenderer {
+internal abstract class OrbitAnalyser : RequiredVesselSupervisedWindowRenderer {
   protected OrbitAnalyser(PrincipiaPluginAdapter adapter,
                           PredictedVessel predicted_vessel) : base(
       adapter,
@@ -222,6 +222,10 @@ protected override void RenderWindowContents(int window_id) {
     using (new UnityEngine.GUILayout.VerticalScope(GUILayoutWidth(12))) {
       if (should_request_analysis) {
         mission_duration_.Render(enabled : true);
+        // If the main window is hidden, make sure that the orbit analyser
+        // refreshes (not at a reduced rate).
+        last_background_analysis_time_ = null;
+        RequestAnalysis();
       }
       var multiline_style = Style.Multiline(UnityEngine.GUI.skin.label);
       float two_lines = multiline_style.CalcHeight(

ksp_plugin_adapter/window_renderer.cs

@@ -131,7 +131,7 @@ public void RenderWindow() {
       skin_ = MakeSkin(UnityEngine.GUI.skin);
     }
     UnityEngine.GUI.skin = skin_;
-    if (show_) {
+    if (Shown()) {
       // NOTE: Calling `Shrink` here (in a Layout, before drawing the window)
       // satisfies the conditions noted in its doc comment and is safe.
       Shrink();
@@ -253,7 +253,8 @@ public void Show() {
     show_ = true;
   }
 
-  public bool Shown() {
+  // Virtual because subclasses may impose extra conditions to show a window.
+  public virtual bool Shown() {
     return show_;
   }
 
@@ -386,6 +387,24 @@ protected void RenderButton(string text,
   private readonly PredictedVessel predicted_vessel_;
 }
 
+// Same as above, but the window is hidden if there is no predicted vessel.
+// This avoids displaying stray close buttons and ephemeral windows.
+internal abstract class
+    RequiredVesselSupervisedWindowRenderer : VesselSupervisedWindowRenderer {
+  protected RequiredVesselSupervisedWindowRenderer(
+      ISupervisor supervisor,
+      PredictedVessel predicted_vessel,
+      params UnityEngine.GUILayoutOption[] options) : base(
+      supervisor,
+      predicted_vessel,
+      options) {
+  }
+
+  public override bool Shown() {
+    return predicted_vessel != null && base.Shown();
+  }
+}
+
 // A window without a supervisor is effectively modal.
 internal abstract class UnsupervisedWindowRenderer : BaseWindowRenderer {
   protected UnsupervisedWindowRenderer(