The corner pin node is used to distort an image in the compositor, but I don't like typing vector offsets manually. Can I do this with a GUI instead? In other words, can I drag around corner points on a screen, without having to re-render UV coordinates from the render engine?
You can use the Movie Clip Editor 'tracking tools' to provide the vectors.
- Open an MCE window and import your clip. Check the dimensions in the properties panel by pressing the N-key. You should see the image's Dim x and Dim y value as "Size"
- Add four trackers ctrl-click from top left clockwise to bottom left.
- Open the Compositor and add to your image a Corner Pin node.
- Then add a Track Position node / Map Range node (x2) / Combine RGB node.
- Set the Map range node for the track position x value to Dim x (from the tracker properties panel), with 0 as the minimum.
- Set the Map range node for the track position y value to Dim y, with 0 as the minimum.
- Send the Map range node 'results for x' to the RED input of the Combine RGB node
- Send the Map range node 'results for y' to the GREEN input of the Combine RGB node
Repeat for all four corners, or duplicate the group of 4 nodes 4 times.