Transformation tool specification

intro

This is the specification for the unified transformation tool.

This tool has been designed to achieve some very specific goals:

1. it is a tool for users who know what they are doing, at a pace of a around two actions per second; this tool stays out of their way and does not make them think;
2. it is a tool to work on pixels creatively, more by feeling than by numbers; together with point #1 we try to facilitate a positive feedback loop where the result of the last transformation input inspires the next few steps;
3. it is a tool to supersede the move, scale and shear tools, in a drive to slim down the toolbox; this means that simple things need to remain simple;
4. it is a tool to provide a more freewheeling alternative to the rotate and perspective tools; as a follow-up to this design the rotate and perspective need a serious refresh—to for instance support getting horizons really horizontal and verticals really vertical for photographers.