Use up and down arrows to adjust brightness.

Polarity is now the right way.

power_console_common.h

@@ -46,6 +46,28 @@ class MouseWheelSlider : public Fl_Value_Slider
 				}
 				break;
 
+				case FL_KEYBOARD:
+				{
+					const auto key= Fl::event_key();
+					if( key != FL_Down and key != FL_Up )
+					{
+						return this->Fl_Value_Slider::handle( event );
+					}
+
+					const int polarity= Fl::event_key() == FL_Down ? +1 : -1;
+					const int newVal= value() + polarity * step();
+					if( newVal >= maximum()
+							and newVal <= minimum() )
+					{
+						value( newVal );
+					}
+
+					do_callback();
+
+					return 1;
+				}
+				break;
+
 				default:
 				{
 					return this->Fl_Value_Slider::handle( event );