Unified implementation of filters for CloneSources

All filters now derive from FrameBufferFilter, which is always used in a CloneSource. Default FrameBufferFilter is Passthrough filter. Others are Delay and Image filters. Implemented UI selection of filter type, XML session save and load. Linked ImageFilter to Code editor.

DelayFilter.h

@@ -0,0 +1,43 @@
+#ifndef DELAYFILTER_H
+#define DELAYFILTER_H
+
+#include <queue>
+#include <glm/glm.hpp>
+
+#include "FrameBufferFilter.h"
+
+class Surface;
+class FrameBuffer;
+
+class DelayFilter : public FrameBufferFilter
+{
+public:
+    DelayFilter();
+    ~DelayFilter();
+
+    // delay property
+    inline void setDelay(double second) { delay_ = second; }
+    inline double delay() const { return delay_; }
+
+    // implementation of FrameBufferFilter
+    Type type() const { return FrameBufferFilter::FILTER_DELAY; }
+    uint texture () const override;
+    glm::vec3 resolution () const override;
+    void update (float dt) override;
+    void draw   (FrameBuffer *input) override;
+    void accept (Visitor& v) override;
+
+private:
+    // queue of frames
+    std::queue<FrameBuffer *> frames_;
+    std::queue<double> elapsed_;
+
+    // render management
+    FrameBuffer *temp_frame_;
+
+    // time management
+    double now_;
+    double delay_;
+};
+
+#endif // DELAYFILTER_H