Some highlights:
1) The new implementation gives much better transformation quality,
   because it calculates correct offsets inside the pixel. The comparison
   of the images can be found on page [0]
2) The rotation is now 2-pass instead of 3-pass it used before. There is
   almost no difference in quality (I'm not sure that initially the third
   pass was introduced for quality reasons). This speeds up the rotation
   by 40%.
3) Some fast-path optimizations are done for the pure shear operations,
   which make up to two times better performance.
4) Implemented a simple wrapper for the progress updates
   (ProgressUpdateHelper)


[0] - http://krita.org/item/126-focus-on-transformations