transform

Affine 2D transformation matrix class.

The Transform class implements various transformation matrix operations, both on the matrix itself, as well as on 2D coordinates.

Transform instances are effectively immutable: all methods that operate on the transformation itself always return a new instance. This has as the interesting side effect that Transform instances are hashable, ie. they can be used as dictionary keys.

This module exports the following symbols:

Transform

this is the main class

Identity

Transform instance set to the identity transformation

Offset

Convenience function that returns a translating transformation

Scale

Convenience function that returns a scaling transformation

Example

>>> t = Transform(2, 0, 0, 3, 0, 0)
>>> t.transformPoint((100, 100))
(200, 300)
>>> t = Scale(2, 3)
>>> t.transformPoint((100, 100))
(200, 300)
>>> t.transformPoint((0, 0))
(0, 0)
>>> t = Offset(2, 3)
>>> t.transformPoint((100, 100))
(102, 103)
>>> t.transformPoint((0, 0))
(2, 3)
>>> t2 = t.scale(0.5)
>>> t2.transformPoint((100, 100))
(52.0, 53.0)
>>> import math
>>> t3 = t2.rotate(math.pi / 2)
>>> t3.transformPoint((0, 0))
(2.0, 3.0)
>>> t3.transformPoint((100, 100))
(-48.0, 53.0)
>>> t = Identity.scale(0.5).translate(100, 200).skew(0.1, 0.2)
>>> t.transformPoints([(0, 0), (1, 1), (100, 100)])
[(50.0, 100.0), (50.550167336042726, 100.60135501775433), (105.01673360427253, 160.13550177543362)]
>>>

fontTools.misc.transform.Offset(x=0, y=0)

Return the identity transformation offset by x, y.

Example

>>> Offset(2, 3)
<Transform [1 0 0 1 2 3]>
>>>

fontTools.misc.transform.Scale(x, y=None)

Return the identity transformation scaled by x, y. The ‘y’ argument may be None, which implies to use the x value for y as well.

Example

>>> Scale(2, 3)
<Transform [2 0 0 3 0 0]>
>>>

class fontTools.misc.transform.Transform(xx: float = 1, xy: float = 0, yx: float = 0, yy: float = 1, dx: float = 0, dy: float = 0)

2x2 transformation matrix plus offset, a.k.a. Affine transform. Transform instances are immutable: all transforming methods, eg. rotate(), return a new Transform instance.

Example

>>> t = Transform()
>>> t
<Transform [1 0 0 1 0 0]>
>>> t.scale(2)
<Transform [2 0 0 2 0 0]>
>>> t.scale(2.5, 5.5)
<Transform [2.5 0 0 5.5 0 0]>
>>>
>>> t.scale(2, 3).transformPoint((100, 100))
(200, 300)

Transform’s constructor takes six arguments, all of which are optional, and can be used as keyword arguments:

>>> Transform(12)
<Transform [12 0 0 1 0 0]>
>>> Transform(dx=12)
<Transform [1 0 0 1 12 0]>
>>> Transform(yx=12)
<Transform [1 0 12 1 0 0]>

Transform instances also behave like sequences of length 6:

>>> len(Identity)
6
>>> list(Identity)
[1, 0, 0, 1, 0, 0]
>>> tuple(Identity)
(1, 0, 0, 1, 0, 0)

Transform instances are comparable:

>>> t1 = Identity.scale(2, 3).translate(4, 6)
>>> t2 = Identity.translate(8, 18).scale(2, 3)
>>> t1 == t2
1

But beware of floating point rounding errors:

>>> t1 = Identity.scale(0.2, 0.3).translate(0.4, 0.6)
>>> t2 = Identity.translate(0.08, 0.18).scale(0.2, 0.3)
>>> t1
<Transform [0.2 0 0 0.3 0.08 0.18]>
>>> t2
<Transform [0.2 0 0 0.3 0.08 0.18]>
>>> t1 == t2
0

Transform instances are hashable, meaning you can use them as keys in dictionaries:

>>> d = {Scale(12, 13): None}
>>> d
{<Transform [12 0 0 13 0 0]>: None}

But again, beware of floating point rounding errors:

>>> t1 = Identity.scale(0.2, 0.3).translate(0.4, 0.6)
>>> t2 = Identity.translate(0.08, 0.18).scale(0.2, 0.3)
>>> t1
<Transform [0.2 0 0 0.3 0.08 0.18]>
>>> t2
<Transform [0.2 0 0 0.3 0.08 0.18]>
>>> d = {t1: None}
>>> d
{<Transform [0.2 0 0 0.3 0.08 0.18]>: None}
>>> d[t2]
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
KeyError: <Transform [0.2 0 0 0.3 0.08 0.18]>

count(value, /)

Return number of occurrences of value.

dx: float

Alias for field number 4

dy: float

Alias for field number 5

index(value, start=0, stop=9223372036854775807, /)

Return first index of value.

Raises ValueError if the value is not present.

inverse()

Return the inverse transformation.

Example

>>> t = Identity.translate(2, 3).scale(4, 5)
>>> t.transformPoint((10, 20))
(42, 103)
>>> it = t.inverse()
>>> it.transformPoint((42, 103))
(10.0, 20.0)
>>>

reverseTransform(other)

Return a new transformation, which is the other transformation transformed by self. self.reverseTransform(other) is equivalent to other.transform(self).

Example

>>> t = Transform(2, 0, 0, 3, 1, 6)
>>> t.reverseTransform((4, 3, 2, 1, 5, 6))
<Transform [8 6 6 3 21 15]>
>>> Transform(4, 3, 2, 1, 5, 6).transform((2, 0, 0, 3, 1, 6))
<Transform [8 6 6 3 21 15]>
>>>

rotate(angle)

Return a new transformation, rotated by ‘angle’ (radians).

Example

>>> import math
>>> t = Transform()
>>> t.rotate(math.pi / 2)
<Transform [0 1 -1 0 0 0]>
>>>

scale(x=1, y=None)

Return a new transformation, scaled by x, y. The ‘y’ argument may be None, which implies to use the x value for y as well.

Example

>>> t = Transform()
>>> t.scale(5)
<Transform [5 0 0 5 0 0]>
>>> t.scale(5, 6)
<Transform [5 0 0 6 0 0]>
>>>

skew(x=0, y=0)

Return a new transformation, skewed by x and y.

Example

>>> import math
>>> t = Transform()
>>> t.skew(math.pi / 4)
<Transform [1 0 1 1 0 0]>
>>>

toPS()

Return a PostScript representation

Example

>>> t = Identity.scale(2, 3).translate(4, 5)
>>> t.toPS()
'[2 0 0 3 8 15]'
>>>

transform(other)

Return a new transformation, transformed by another transformation.

Example

>>> t = Transform(2, 0, 0, 3, 1, 6)
>>> t.transform((4, 3, 2, 1, 5, 6))
<Transform [8 9 4 3 11 24]>
>>>

transformPoint(p)

Transform a point.

Example

>>> t = Transform()
>>> t = t.scale(2.5, 5.5)
>>> t.transformPoint((100, 100))
(250.0, 550.0)

transformPoints(points)

Transform a list of points.

Example

>>> t = Scale(2, 3)
>>> t.transformPoints([(0, 0), (0, 100), (100, 100), (100, 0)])
[(0, 0), (0, 300), (200, 300), (200, 0)]
>>>

transformVector(v)

Transform an (dx, dy) vector, treating translation as zero.

Example

>>> t = Transform(2, 0, 0, 2, 10, 20)
>>> t.transformVector((3, -4))
(6, -8)
>>>

transformVectors(vectors)

Transform a list of (dx, dy) vector, treating translation as zero.

Example

>>> t = Transform(2, 0, 0, 2, 10, 20)
>>> t.transformVectors([(3, -4), (5, -6)])
[(6, -8), (10, -12)]
>>>

translate(x=0, y=0)

Return a new transformation, translated (offset) by x, y.

Example

>>> t = Transform()
>>> t.translate(20, 30)
<Transform [1 0 0 1 20 30]>
>>>

xx: float

Alias for field number 0

xy: float

Alias for field number 1

yx: float

Alias for field number 2

yy: float

Alias for field number 3