General (affine) transformations, represented by an invertible linear map, its transpose, and a vector representing a translation component.

By the transpose of a linear map we mean simply the linear map corresponding to the transpose of the map's matrix representation. For example, any scale is its own transpose, since scales are represented by matrices with zeros everywhere except the diagonal. The transpose of a rotation is the same as its inverse.

The reason we need to keep track of transposes is because it turns out that when transforming a shape according to some linear map L, the shape's normal vectors transform according to L's inverse transpose. (For a more detailed explanation and proof, see https://wiki.haskell.org/Diagrams/Dev/Transformations.) This is exactly what we need when transforming bounding functions, which are defined in terms of perpendicular (i.e. normal) hyperplanes.

For more general, non-invertible transformations, see Diagrams.Deform (in diagrams-lib).

Invert a transformation.

Get the translational component of a transformation.

Apply a transformation to a vector. Note that any translational component of the transformation will not affect the vector, since vectors are invariant under translation.

Apply a transformation to a point.

Type class for things t which can be transformed.

Create a translation.

Translate by a vector.

Translate the object by the translation that sends the origin to the given point. Note that this is dual to moveOriginTo, i.e. we should have

  moveTo (origin .^+ v) === moveOriginTo (origin .^- v)
  

For types which are also Transformable, this is essentially the same as translate, i.e.

  moveTo (origin .^+ v) === translate v
  

A flipped variant of moveTo, provided for convenience. Useful when writing a function which takes a point as an argument, such as when using withName and friends.

Create a uniform scaling transformation.

Scale uniformly in every dimension by the given scalar.

Conjugate one transformation by another. conjugate t1 t2 is the transformation which performs first t1, then t2, then the inverse of t1.

Carry out some transformation "under" another one: f `underT` t first applies t, then f, then the inverse of t. For example, scaleX 2 `underT` rotation (-1/8 @@ Turn) is the transformation which scales by a factor of 2 along the diagonal line y = x.

Note that

(transform t2) underT t1 == transform (conjugate t1 t2)

for all transformations t1 and t2.

See also the isomorphisms like transformed, movedTo, movedFrom, and translated.

Use a Transformation to make an Iso between an object transformed and untransformed. This is useful for carrying out functions under another transform:

under (transformed t) f               == transform (inv t) . f . transform t
under (transformed t1) (transform t2) == transform (conjugate t1 t2)
transformed t ## a                    == transform t a
a ^. transformed t                    == transform (inv t) a

Use a vector to make an Iso between an object translated and untranslated.

under (translated v) f == translate (-v) . f . translate v
translated v ## a      == translate v a
a ^. translated v      == translate (-v) a
over (translated v) f  == translate v . f . translate (-v)

Use a Point to make an Iso between an object moved to and from that point:

under (movedTo p) f == moveTo (-p) . f . moveTo p
over (movedTo p) f  == moveTo p . f . moveTo (-p)
movedTo p           == from (movedFrom p)
movedTo p ## a      == moveTo p a
a ^. movedTo p      == moveOriginTo p a

Use a Transformation to make an Iso between an object transformed and untransformed. We have

under (movedFrom p) f == moveTo p . f . moveTo (-p)
movedFrom p           == from (movedTo p)
movedFrom p ## a      == moveOriginTo p a
a ^. movedFrom p      == moveTo p a
over (movedFrom p) f  == moveTo (-p) . f . moveTo p

Class of types which have an intrinsic notion of a "local origin", i.e. things which are not invariant under translation, and which allow the origin to be moved.

One might wonder why not just use Transformable instead of having a separate class for HasOrigin; indeed, for types which are instances of both we should have the identity

  moveOriginTo (origin .^+ v) === translate (negated v)
  

The reason is that some things (e.g. vectors, Trails) are transformable but are translationally invariant, i.e. have no origin.

Move the local origin by a relative vector.