reworked and vastly improved snapping subsystem

app/widget/timebased/timebasedwidget.h

@@ -25,13 +25,15 @@
 
 #include "node/output/viewer/viewer.h"
 #include "timeline/timelinecommon.h"
+#include "widget/keyframeview/keyframeviewinputconnection.h"
 #include "widget/resizablescrollbar/resizabletimelinescrollbar.h"
 #include "widget/timebased/timescaledobject.h"
 #include "widget/timelinewidget/view/timelineview.h"
-#include "widget/timeruler/timeruler.h"
 
 namespace olive {
 
+class TimeRuler;
+
 class TimeBasedWidget : public TimelineScaledWidget
 {
   Q_OBJECT
@@ -54,6 +56,22 @@ public:
 
   virtual bool eventFilter(QObject* object, QEvent* event) override;
 
+  using SnapMask = uint32_t;
+  enum SnapPoints {
+    kSnapToClips = 0x1,
+    kSnapToPlayhead = 0x2,
+    kSnapToMarkers = 0x4,
+    kSnapToKeyframes = 0x8,
+    kSnapAll = UINT32_MAX
+  };
+
+  /**
+   * @brief Snaps point `start_point` that is moving by `movement` to currently existing clips
+   */
+  bool SnapPoint(const std::vector<rational> &start_times, rational *movement, SnapMask snap_points = kSnapAll);
+  void ShowSnaps(const std::vector<rational> &times);
+  void HideSnaps();
+
 public slots:
   void SetTime(const rational &time);
 
@@ -119,6 +137,10 @@ protected:
 
   void PassWheelEventsToScrollBar(QObject* object);
 
+  virtual const QVector<Block*> *GetSnapBlocks() const { return nullptr; }
+  virtual const QVector<KeyframeViewInputConnection*> *GetSnapKeyframes() const { return nullptr; }
+  virtual const std::vector<NodeKeyframe*> *GetSnapIgnoreKeyframes() const { return nullptr; }
+
 protected slots:
   /**
    * @brief Slot to center the horizontal scroll bar on the playhead's current position
@@ -141,7 +163,7 @@ signals:
   void ConnectedNodeChanged(ViewerOutput* old, ViewerOutput* now);
 
 private:
-  
+
 
   /**
    * @brief Set either in or out point to the current playhead