I am interested in implementing Unified transform tool in GIMP. I went
through the specifications (
http://gui.gimp.org/index.php/Transformation_tool_specification) for the
same. First of all honestly speaking, I found the idea really cool and even
though I am not selected to do this project I would definitely love to see
this tool been added to gimp, as it would definitely help me a lot as a
user. Now, for the doubts regarding it.

   - In the undo section it is mentioned that until the final pixel
   recalculation is done user should be able to undo every single step, though
   after that user should be able to undo the aggregate transformation only.
   Does this means that we would have to maintain another action stack just for
   unified transformation tool, or does gimp currently also maintains two
   different stacks, one for the current tool and one global stack for actions.
   If this is the case some reference to where it happens in code would be

   - In the shaping up section, it is mentioned that the shape of
   transformation frame will change with every transformation and the
   width/height of the frame will be minimum width/height between the two
   sides/4. On the higher end it is clamped to 50 pixels, I believe that
   sometimes while doing perspective transformation this minimum distance can
   get pretty small which could make things a bit messy. Shouldn't we also have
   a limit on the minimum width of frame too, since we would have to put the
   marker for shear, and rotate also in those frames.

   - In the corners of the frame the perspective markers and the scale
   markers are a bit confusing, obv this tool is for people who know what they
   are doing, but still. I have a few ideas in my mind regarding this, I would
   try and make some images for the same and put them up in the discussion page
   ( i guess that should be fair enough).

   - How do we set up the corners of the transform frame after doing some
   transformations, they would be very easily converted into quadrilaterals,
   and sometimes pretty odd looking quadrilaterals, in which placing the
   perspective and scale markers would be even more complex.

   - How do we change the rotation axis, suppose i dont want to rotate my
   selection around the centre of the rectangle, there doesnt seems to be any
   discussion regarding this over that page. I guess a neat idea would be to
   hide the move marker when a person clicks on rotation marker on the frame
   and make rotation marker permanent, after that till the user doesn't clicks
   on any other marker on the frame it should remain in the rotation__waiting
   state only. The only problem with it would be that aa user would not be able
   to use move marker just after rotation, but to do that he would have to
   click anywhere else on the frame first.

   - How do I select a non-rectangular region for transformations?

Also, in my personal opinion, instead of changing the shape of transform
frame with every operation it would be neater to keep it always rectangular
where the size and position of rectangle is determined by the bounding box
for the current transformation area, it could be any shape. And the current
transformation area can be highlighted with dotted lines as it is done
currently with most of the selection tools. This would solve many issues
with restructuring of the frame after every transformation, and would make
things pretty simple in my opinion.

Also, I had problems understanding transformation constraints, it would be
really nice of someone to explain that.

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