New mechanism for source update with callbacks

Similarly to Node update callbacks, sources now have SourceCallbacks called at the start of each update. Several SourceCallback are implemented to ensure thread safe update of more complex properties (mixing alpha, depth, etc.).

Source.h

@@ -4,9 +4,11 @@
 #include <string>
 #include <map>
 #include <atomic>
+#include <mutex>
 #include <list>
 
 #include "View.h"
+#include "SourceCallback.h"
 
 #define DEFAULT_MIXING_TRANSLATION -1.f, 1.f
 
@@ -23,6 +25,7 @@
 #define ICON_SOURCE_CLONE 9, 2
 #define ICON_SOURCE 12, 11
 
+class SourceCallback;
 class ImageShader;
 class MaskShader;
 class ImageProcessingShader;
@@ -56,6 +59,9 @@ public:
 
     void copy(SourceCore const& other);
 
+    // alpha transfer function
+    static float alphaFromCordinates(float x, float y);
+
 protected:
     // nodes
     std::map<View::Mode, Group*> groups_;
@@ -136,9 +142,13 @@ public:
     // a Source shall be updated before displayed (Mixing, Geometry and Layer)
     virtual void update (float dt);
 
+    // add callback to each update
+    void call(SourceCallback *callback, bool override = false);
+
     // update mode
     inline  bool active () const { return active_; }
     virtual void setActive (bool on);
+    void setActive (float threshold);
 
     // lock mode
     inline  bool locked () const { return locked_; }
@@ -178,14 +188,9 @@ public:
     void setMask (FrameBufferImage *img);
     void storeMask (FrameBufferImage *img = nullptr);
 
-    // operations on depth
+    // get properties
     float depth () const;
-    void  setDepth (float d);
-
-    // operations on alpha
-    float mix_distance ();
     float alpha () const;
-    void  setAlpha (float a);
 
     // groups for mixing
     MixingGroup *mixingGroup() const { return mixinggroup_; }
@@ -304,6 +309,8 @@ protected:
     bool  need_update_;
     float dt_;
     Workspace  workspace_;
+    std::list<SourceCallback *> update_callbacks_;
+    std::mutex access_callbacks_;
 
     // clones
     CloneList clones_;