We talked about this with @Gasparoken. We need a new TransformationState similar to MovingPixelsState but more generic.

As a first step this new state will be internal and only for testing purposes. The state should be useful to transform a rectangular shape into any form with a transformation matrix (or maybe more). This state should be as generic as a SelectBoxState+SelectBoxDelegate (so we will need a TransformationState+TransformationDelegate too to use the transformation in something useful in the future).

This state will be useful to fix:

• Some items of Refactor internal selection manager #1459 (mainly Simple Selection Scaling & Saving Settings/Macros #1378 and Create a new selection mode for timeline and color bar/palette #1498)

• Skew transformation Skew/shear tool/transformation #71

• Free transformation Free distort transformation #1437

• And an easier way to transform rectangular-like tools like Rectangle and Ellipse (tools with a TwoPointsController). There is a point about this in Pixel-art friendly features & tweaks #1387:

  Alternative mode to create planned rectangle/ellipse shapes before the final fill/stroke. (Ref 1, Ref 2, Ref 3)

• Resize reference layers Improve "reference layer" feature #1321

Basically the state should have:

1. An input: a rectangle
2. An output: a transformation (preferably a transformation matrix and maybe a set of points for free transformation, like Transformation in PixelsMovement) and the transformed points/rectangle.

Ask to @dacap before you start working on this issue.

Notes: There are some online examples about the relationship between the transformation matrix <-> what we should see in the editor:

• http://www.senocular.com/flash/tutorials/transformmatrix/
• https://ncase.me/matrix/