1) Just create a Transform Mask and edit it with usual Transform Tool
2) All the transformation modes are supported.
2.1) Affine transforms (Free and Perspective) have dynamic preview. That
     is you can paint on a layer and the mask will be updated dynamically
2.1) The other types are updated "statically", that is after 3 sec after
     the last change in the original layer.

Question for testers: isn't this 3 sec delay too long? Probably we should
                      make it shorter?

3) The transformation is written into the mask after you click Apply button.
4) The quality of the affine preview and the final transform (after 3 sec
   delay) differs a bit. That is expected.
5) You can also apply a transform mask onto a Clone Layer, which will
   allow you painting in 3D-perspective dynamically.

Please test it in krita-chili-kazakov branch :)

CCMAIL:kimageshop@kde.org