implemented transition moving

For dual transitions, this will shift around the mid point.

app/widget/timelinewidget/tool/tool.cpp

@@ -23,6 +23,7 @@
 #include <float.h>
 
 #include "common/range.h"
+#include "node/block/transition/transition.h"
 
 TimelineWidget::Tool::Tool(TimelineWidget *parent) :
   dragging_(false),
@@ -101,6 +102,23 @@ rational TimelineWidget::Tool::ValidateFrameMovement(rational movement, const QV
       continue;
     }
 
+    Block* block = Node::ValueToPtr<Block>(ghost->data(TimelineViewGhostItem::kAttachedBlock));
+
+    if (block && block->type() == Block::kTransition) {
+      TransitionBlock* transition = static_cast<TransitionBlock*>(block);
+
+      // Daul transitions are only allowed to move so that neither of their offsets are < 0
+      if (transition->connected_in_block() && transition->connected_out_block()) {
+        if (movement > transition->out_offset()) {
+          movement = transition->out_offset();
+        }
+
+        if (movement < -transition->in_offset()) {
+          movement = -transition->in_offset();
+        }
+      }
+    }
+
     // Prevents any ghosts from going below 0:00:00 time
     if (ghost->In() + movement < 0) {
       movement = -ghost->In();