Codechange: Move volume control slider logic to separate functions

src/widgets/slider_func.h

@@ -0,0 +1,21 @@
+/*
+ * This file is part of OpenTTD.
+ * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
+ * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/** @file slider_type.h Types related to the horizontal slider widget. */
+
+#ifndef WIDGETS_SLIDER_TYPE_H
+#define WIDGETS_SLIDER_TYPE_H
+
+#include "../window_type.h"
+#include "../gfx_func.h"
+
+
+void DrawVolumeSliderWidget(Rect r, byte value);
+bool ClickVolumeSliderWidget(Rect r, Point pt, byte &value);
+
+
+#endif /* WIDGETS_SLIDER_TYPE_H */