ClassCurve

1. summary Draw functions and parametric curves
2. labels Reference,Version1

_(This page applies only to the 1.x branch of SVGFig.)_

class Curve

Curve draws a Python callable as a path. Curves are adaptively sampled, meaning that the function is evaluated at more points near corners and along curves and at fewer points along straight segments. If the function is discontinuous (like a step function), the path will be a broken line.

The sampling algorithm starts at the endpoints and bisects until three consecutive points are nearly linear, or until reaching a recursion limit.

Arguments

• Curve(f, low, high, loop, attribute=value)*

	f		_*required*_		a Python callable or string in the form "f(t), g(t)"
	low, high		_*required*_		left and right endpoints
	loop		_default_=False		if True, connect the endpoints
	attribute=value pairs		_keyword list_		SVG attributes

The function must take one argument and return two values. If it is a string, it will be passed to [DefFuncRtoR2 funcRtoR2]. For complex functions, use an explicit call to [DefFuncRtoC funcRtoC] and for real functions, use an explicit call to [DefFuncRtoR funcRtoR], which return a function in the right format.

The following are all equivalent:

• `Curve(lambda t: t, t2, 0, 1)`
• `Curve("t, t2", 0, 1)`
• `Curve(funcRtoR2("t, t2"), 0, 1)`
• `Curve(funcRtoC("t + (1j)*t2"), 0, 1)`
• `Curve(funcRtoR("x2"), 0, 1)`

SVG method

Curve has an *SVG* method, as described in [GeneralPrimitive General features for all primitives].

Path method

Curve has a *Path* method, as described in [GeneralPrimitive General features for all primitives].

Defaults

Curve has the following defaults, as described in [GeneralPrimitive General features for all primitives].

	random_sampling		True		if False, bisect with a point exactly halfway between pairs of points; if True, randomly choose a point between 30% and 70%
	recursion_limit		15		number of subdivisions before giving up; if 15, sampling algorithm can visit _at most_ 2^15^ points
	linearity_limit		0.05		maximum deviation (in SVG units) from a straight line
	discontinuity_limit		5		minimum deviation (in SVG units) between points that is considered continuous

Special data members

After the Curve has been evaluated with *SVG* or *Path*, it gains a new data memeber, `last_samples`. This is an iterable of Curve.Sample objects:

>>> c = Curve(funcRtoR("x**2"), 0, 1)
>>> c.SVG()
>>> for s in c.last_samples:
...     print s.x, s.y, s.X, s.Y
...

Curve.Sample has four data members, `x`, `y`, `X`, `Y`. These are coordinates in local (lowercase) and global (uppercase) coordinates. If a coordinate is `None`, there is a break in the curve, due to a discontinuity in the supplied function.

This iterable is actually a doubly-linked list, not a Python construct, connected through data members called `left` and `right`.