2d-spiral functions. Includes archimedean and logarithmic generic spirals. Useful to draw spiral paths in canvas, svg etc.

Usage

var spiral = require('spiral-2d/logarithmic');

//paint spiral curve in canvas
context.beginPath();
var center = [50, 50];
context.moveTo(center[0], center[1]);
for (var angle = 0; angle <= Math.PI * 4; angle+=0.01) {
	var coords = spiral(center, angle);
	context.lineTo(coords[0], coords[1]);
}
context.stroke();

//fill spiral sector
context.beginPath();
var center = [center[0], center[1]];
context.moveTo(spiral(center, Math.PI * 2));
for (var angle = Math.PI * 2; angle <= Math.PI * 3; angle+=0.01) {
	var coords = spiral(center, angle);
	context.lineTo(coords[0], coords[1]);
}
context.lineTo(spiral(center, Math.PI * 5));
for (var angle = Math.PI * 5; angle >= Math.PI * 4; angle-=0.01) {
	var coords = spiral(center, angle);
	context.lineTo(coords[0], coords[1]);
}
context.lineTo(spiral(center, Math.PI * 2));
context.fill();

API

//include the whole module (logarithmic spiral by default)
var spiral = require('spiral-2d');

//or include just part
var archimedean = require('spiral-2d/archimedean');
var logarithmic = require('spiral-2d/logarithmic');

//get coordinates of a spiral point for passed params
logarithmic(centerXY, angleInRadians, a, b);
archimedean(centerXY, angleInRadians, a, b, c?);

//get radius of spiral params
logarithmic.radius(angleInRadians, a, b);
archimedean.radius(angleInRadians, a, b, c?);

//get angle of spiral params
logarithmic.angle(radius, a, b);
archimedean.angle(radius, a, b, c?);

//get a/b properies of spirals (to adjust size etc)
logarithmic.a(radius, angle, b);
archimedean.a(radius, angle, b, c?);
logarithmic.b(radius, angle, a);
archimedean.b(radius, angle, a, c?);

Most of spirals fall into one of two kinds of generic spirals:

//Golden, or fibonacci spiral https://en.wikipedia.org/wiki/Golden_spiral
logarithmic(center, angle, a, 0.3063489);

//Hyperbolic spiral https://en.wikipedia.org/wiki/Hyperbolic_spiral
archimedean(center, angle, 0, a, -1);

//Fermat’s spiral https://en.wikipedia.org/wiki/Fermat%27s_spiral
archimedean(center, angle, 0, 1, 2);

//Lituus https://en.wikipedia.org/wiki/Lituus_(mathematics)
archimedean(center, angle, 0, 1, -2);

TODO

• Euler spiral
• Involute