Introducing TweakOperator, for better tool's special mode handling

rtengine/tweakoperator.h

@@ -0,0 +1,45 @@
+/*
+ *  This file is part of RawTherapee.
+ *
+ *  Copyright (c) 2019 Jean-Christophe FRISCH <natureh.510@gmail.com>
+ *
+ *  RawTherapee 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, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  RawTherapee 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 RawTherapee.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#pragma once
+
+namespace rtengine
+{
+
+namespace procparams
+{
+
+class ProcParams;
+
+}
+
+/** This class can let objects alter the collected values of the ProcParams for a specific
+ *  purpose, e.g. displaying a preview image at a specific point in the pipeline or with
+ *  disabled tools. Before starting the rendering, the engine will call the TweakOperator
+ *  (if set) to modify the ProcParams. The untweaked one will still exist as a backup, and
+ *  can be sent back if necessary.  */
+class TweakOperator
+{
+public:
+    virtual ~TweakOperator() {}
+
+    /** Callback that will alter the ProcParams before hte image is computed. */
+    virtual void tweakParams(procparams::ProcParams& pparams) = 0;
+};
+
+}