Spot Removal tool

It is not working yet, but the GUI is (almost) done.
See issue #2239.

rtengine/alpha.cc

@@ -0,0 +1,75 @@
+/*
+ *  This file is part of RawTherapee.
+ *
+ *  Copyright (c) 2004-2010 Gabor Horvath <hgabor@rawtherapee.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/>.
+ */
+
+#include "alpha.h"
+
+namespace rtengine
+{
+
+Alpha::Alpha () {}
+
+Alpha::Alpha (int width, int height)
+{
+    if (width > 0 && height > 0) {
+        surface = Cairo::ImageSurface::create(Cairo::FORMAT_A8, width, height);
+    }
+}
+
+/*
+Alpha::~Alpha () {
+    surface->unreference();
+}
+*/
+
+void Alpha::setSize(int width, int height)
+{
+    if (width > 0 && height > 0) {
+        if (surface) {
+            if (width != getWidth() && height != getHeight()) {
+                surface.clear();  // does this delete the referenced object? Unreferencing doesn't work, since Cairo expect to have a non null refCount in the destructor!
+            } else {
+                return;
+            }
+        }
+
+        surface = Cairo::ImageSurface::create(Cairo::FORMAT_A8, width, height);
+    } else if (surface) {
+        surface.clear();
+    }
+}
+
+int Alpha::getWidth()
+{
+    if (surface) {
+        return surface->get_width();
+    }
+
+    return -1;
+}
+
+int Alpha::getHeight()
+{
+    if (surface) {
+        return surface->get_height();
+    }
+
+    return -1;
+}
+
+}