A close window button.

ksp_plugin_adapter/flight_planner.cs

@@ -52,7 +52,7 @@ class FlightPlanner : VesselSupervisedWindowRenderer {
   protected override string Title =>
       L10N.CacheFormat("#Principia_FlightPlan_Title");
 
-  protected override void RenderWindow(int window_id) {
+  protected override void RenderWindowContents(int window_id) {
     // We must ensure that the GUI elements don't change between Layout and
     // Repaint.  This means that any state change must occur before Layout or
     // after Repaint.  This if statement implements the former.  It updates the

ksp_plugin_adapter/main_window.cs

@@ -142,7 +142,7 @@ internal class MainWindow : VesselSupervisedWindowRenderer {
 
   protected override string Title => "Principia";
 
-  protected override void RenderWindow(int window_id) {
+  protected override void RenderWindowContents(int window_id) {
     using (new UnityEngine.GUILayout.VerticalScope()) {
       if (!adapter_.PluginRunning()) {
         UnityEngine.GUILayout.Label(

ksp_plugin_adapter/orbit_analyser.cs

@@ -191,7 +191,7 @@ internal abstract class OrbitAnalyser : VesselSupervisedWindowRenderer {
                                                ToUpper() +
                                            orbit_description_.Substring(1);
 
-  protected override void RenderWindow(int window_id) {
+  protected override void RenderWindowContents(int window_id) {
     string vessel_guid = predicted_vessel?.id.ToString();
     if (vessel_guid == null) {
       return;

ksp_plugin_adapter/reference_frame_selector.cs

@@ -462,7 +462,7 @@ public enum FrameType {
                        Name(),
                        NavballName());
 
-  protected override void RenderWindow(int window_id) {
+  protected override void RenderWindowContents(int window_id) {
     using (new UnityEngine.GUILayout.VerticalScope()) {
       UnityEngine.GUILayout.Label(
           L10N.CacheFormat(

ksp_plugin_adapter/window_renderer.cs

@@ -267,14 +267,15 @@ internal abstract class BaseWindowRenderer : ScalingRenderer, IConfigNode {
   private UnityEngine.GUISkin skin_;
   private bool must_centre_ = true;
   private bool show_ = false;
-  private UnityEngine.Rect rectangle_;
+  protected UnityEngine.Rect rectangle_;
   private DateTime tooltip_begin_;
   private string tooltip_ = "";
   private UnityEngine.Rect tooltip_rectangle_;
 }
 
 // The supervisor of a window decides when to clear input locks, when to render
-// the window and when to delete it.
+// the window and when to delete it.  A supervised window has a “Hide” button,
+// in addition to the external toggle handled by the supervisor.
 internal abstract class SupervisedWindowRenderer : BaseWindowRenderer {
   public interface ISupervisor {
     event Action LockClearing;
@@ -291,6 +292,20 @@ public interface ISupervisor {
     supervisor_.WindowsRendering += RenderWindow;
   }
 
+  protected abstract void RenderWindowContents(int window_id);
+
+  protected sealed override void RenderWindow(int window_id) {
+    if (UnityEngine.GUI.Button(new UnityEngine.Rect(
+            x: rectangle_.width - Width(1),
+            y: 0,
+            width: Width(1),
+            height: Width(1)),
+            "×")) {
+      Hide();
+    }
+    RenderWindowContents(window_id);
+  }
+
   public void DisposeWindow() {
     supervisor_.LockClearing -= ClearLock;
     supervisor_.WindowsDisposal -= DisposeWindow;