plot::Transform2d

Affine linear transformation of 2D objects

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Syntax

plot::Transform2d(<b2d>, A2d, obj1, <obj2,...>, <a = amin .. amax>, options)

Description

plot::Transform2d(b, A, objects) with a vector b and a matrix A applies the affine linear transformation $$x\to Ax+b$$ to 2D objects.

The transformation matrix A can be specified by a list of lists, with the sublists representing the rows.

[[A1, 1, A1, 2, …], [A2, 1, A2, 2, …], …]

A plain list [A1, 1, A1, 2, A2, 1, A2, 2] represents the matrix row by row.

Transform objects can transform several graphical objects simultaneously. Plotting the transform object renders all graphical objects inside.

Transformed objects have a tendency to overestimate their ViewingBox. In such cases, specify a suitable ViewingBox explicitly.

Transformation objects can be used inside transformation objects. If they are animated, the animations run simultaneously.

Animated transform objects are rather “cheap” concerning computing and storing costs. For more complex graphical objects, it is more efficient to use an animated transform object than to redefine the object for each frame.

The function op allows to extract the graphical objects inside a transformation object.

Attributes

Attribute	Purpose	Default Value
AffectViewingBox	influence of objects on the ViewingBox of a scene	TRUE
Frames	the number of frames in an animation	50
Matrix2d	transformation matrices	[1, 0, 0, 1]
Name	the name of a plot object (for browser and legend)
ParameterEnd	end value of the animation parameter
ParameterName	name of the animation parameter
ParameterBegin	initial value of the animation parameter
ParameterRange	range of the animation parameter
Shift	shift vector	[0, 0]
ShiftX	shift vector	0
ShiftY	shift vector	0
TimeEnd	end time of the animation	10.0
TimeBegin	start time of the animation	0.0
TimeRange	the real time span of an animation	0.0 .. 10.0

Examples

Example 1

Visualize a linear transformation $$x\to Ax$$ without shift:

x1 := plot::Arrow2d([0, 0], [1/3, 1], Color = RGB::Red):
x2 := plot::Arrow2d([0, 0], [1, 1], Color = RGB::Green):
x3 := plot::Arrow2d([0, 0], [1, 1/3], Color = RGB::Blue):
A :=  matrix([[1, -2], [-2, 1]]):
plot(plot::Scene2d(x1, x2, x3),
     plot::Scene2d(plot::Transform2d(A, x1, x2, x3)),
     Scaling = Constrained, Layout = Horizontal):

delete x1, x2, x3, A:

Parameters

b2d	The 2D shift vector: a list with 2 entries. Also vectors generated by matrix and arrays are accepted. The entries must be numerical values or arithmetical expressions of the animation paramater a. b2d is equivalent to the attribute Shift.
A2d	The 2D transformation matrix: a 2×2 matrix, a 2×2 array, a list of 2 lists, or a plain list with 4 entries. The entries must be numerical values or arithmetical expressions of the animation paramater a. A2d is equivalent to the attribute Matrix2d.
obj1, obj2, …	Plot objects
a	Animation parameter, specified as a = amin..amax, where amin is the initial parameter value, and amax is the final parameter value.