Brightness adjustment now supports undo

Start an undo command when the drag begins, and finish it when the mouse is
released (i.e. at the same time the colour picker is updated). This avoids
flooding the undo queue with lots of useless tiny adjustment commands.

The incremental drag event is now wxEVT_SCROLL_THUMBTRACK, since an extra
wxEVT_SLIDER is emitted *after* the final wxEVT_SCROLL_CHANGED event, resulting
in a spurious new undo command being initiated which in turn prevents the
previous command from being undone.

radiant/ui/lightinspector/LightInspector.cpp

@@ -150,11 +150,26 @@ void LightInspector::setupOptionsPanel()
     findNamedObject<wxColourPickerCtrl>(this, "LightInspectorColour")->Bind(
         wxEVT_COLOURPICKER_CHANGED, &LightInspector::_onColourChange, this
     );
-    _brightnessSlider->Bind(
-        wxEVT_SLIDER, [=](wxCommandEvent&) { adjustBrightness(); }
+    _brightnessSlider->Bind( // drag in progress
+        wxEVT_SCROLL_THUMBTRACK,
+        [=](wxScrollEvent&) {
+            if (!_adjustingBrightness && !GlobalUndoSystem().operationStarted())
+            {
+                GlobalUndoSystem().start();
+                _adjustingBrightness = true;
+            }
+            adjustBrightness();
+        }
     );
-    _brightnessSlider->Bind(
-        wxEVT_SCROLL_CHANGED, [=](wxScrollEvent&) { updateColourPicker(); }
+    _brightnessSlider->Bind( // drag finished
+        wxEVT_SCROLL_CHANGED,
+        [=](wxScrollEvent&) {
+            if (_adjustingBrightness) {
+                GlobalUndoSystem().finish("Adjust light brightness");
+                _adjustingBrightness = false;
+            }
+            updateColourPicker();
+        }
     );
 
     findNamedObject<wxCheckBox>(this, "LightInspectorParallel")->Bind(wxEVT_CHECKBOX, &LightInspector::_onOptionsToggle, this);

radiant/ui/lightinspector/LightInspector.h

@@ -48,6 +48,10 @@ class LightInspector :
     // Disables callbacks if set to TRUE (during widget updates)
     bool _updateActive;
 
+    // Track if a brightness adjustment is in progress (which needs an undo
+    // command when finished)
+    bool _adjustingBrightness = false;
+
     bool _supportsAiSee;
 
     sigc::connection _selectionChanged;