Package gaphas :: Module constraint

Module constraint

This module contains several flavors of constraint classes. Each has a method Constraint.solve_for(name) and a method Constraint.mark_dirty(v). These methods are used by the constraint solver (solver.Solver) to set the variables.

Variables should be of type solver.Variable.

See classes' documentation below for constraints description and for examples of their usage.

EqualsConstraint: Make 'a' and 'b' equal.
LessThanConstraint: Ensure one variable stays smaller than the other.
CenterConstraint: Ensures a Variable is kept between two other variables.
EquationConstraint: Solve a linear equation.
BalanceConstraint: Keeps three variables in line, maintaining a specific ratio.
LineConstraint: Solves the equation where a line is connected to a line or side at a specific point.

New constraint class should derive from Constraint class abstract class and implement Constraint.solve_for(Variable) method to update a variable with appropriate value.

Version: $Revision: 1794 $

Classes
	Constraint Constraint base class.
	EqualsConstraint Constraint, which ensures that two arguments `a` and `b` are equal, for example >>> from solver import Variable >>> a, b = Variable(1.0), Variable(2.0) >>> eq = EqualsConstraint(a, b) >>> eq.solve_for(a) >>> a Variable(2, 20) >>> a.value = 10.8 >>> eq.solve_for(b) >>> b Variable(10.8, 20)
	CenterConstraint Simple Constraint, takes three arguments: 'a', 'b' and center.
	LessThanConstraint Ensure `smaller` is less than `bigger`.
	EquationConstraint Equation solver using attributes and introspection.
	BalanceConstraint Ensure that a variable `v` is between values specified by `band` and in distance proportional from `band[0]`.
	LineConstraint Ensure a point is kept on a line.

Variables
	EPSILON = `1e-006`
	ITERLIMIT = `1000`