ITransform

v1.5: added 'root warp knob to dial back the overall warp effect. added knob to define the control channel.

To get the root format's centre by default add the following callback to your init.py:

# auto center for ITransform
def setCenter():
    n = nuke.thisNode()
    n['center'].setValue((n.width() * 0.5, n.height() * 0.5))

nuke.addOnUserCreate(setCenter, nodeClass='ITransform')

v1.4: fixed non-uniform scale

v1.3: re-implemented the skew knobs which got lost when the new skew paremters where introduces in Nuke

v1.2: updated to deal with non-square pixel aspect

v1.1: added option to not crop the result and fixed expressions to work with stereo projects

ITransform uses the IDisplace node under the hood to warp an image based on a control mask.
It's quite handy for controlled warping as it let's you do anything a normal Transform node does, so it's possible to use tracking data to for animated warps etc.

The controls are just like the regular Transform node (though due to a bug in the current Nuke version the center knob may not set itself correctly upon initial node creation)