2D Tracking - Nuke 101: Professional Compositing and Visual Effects - page 230

A green line appears in the DAG showing that a property in CornerPin2D1 is fol-
lowing a property in Tracker1 ( FIGURE 5.27 ).
Figure 5.27. The green line indicates a linking expression.
Let's have you write an expression yourself next.
10. Don't close the Expression panel. Make sure the top row is highlighted and copy
the text with Ctrl/Cmd-C.
11. Click Cancel.
12. Click CornerPin2D1's To2 Animation menu and choose Edit Expression.
13. In the Expression panel that opens, paste the copied expression into the X prop-
erty field.
14. You don't want to copy data from track1 now, so change the last digit to 2, so
you'll have parent.Tracker1.track2.
15. Do the same for the Y expression.
You have now written an expression. How liberating!
16. Perform the same steps, choosing your favorite method, on the other two proper-
ties: To3 and To4 for track3 and track4 respectively.
The Viewer should now display an image that looks like FIGURE 5.28 .
Figure 5.28. The CornerPin node positions the edges of the frame by de-
fault.