Velocitr, velocity and drag helper
4th Jan 2013
I needed a way of applying velocity and drag to a new UI I am putting together, much like the one I built in to jQuery.kinetic. So I have pulled it out in to a simple reusable object.
I have called it Velocitr and it's source is on Github.
Usage
// create an instance
var v = new Velocitr();
// set starting point
v.move(30, true);
// move
v.move(50);
// get velocity
assert(v.velocity).equals(20);
// apply drag
v.drag = 0.9 // => default
v.decelerate()
assert(v.velocity).equals(18);
Chaining
var v = new Velocitr();
v.move(30, true)
.move(60)
.decelerate();
assert(v.velocity).equals(27);
Tests
It comes with a suite of tests which are written with the help of QUnit and Pavlov and can be found in the test/ folder.
I have written a few QUnit tests but this is the first time I used Pavlov and I much prefer the syntax.
Here's a little taster.
pavlov.specify('Velocitr', function(){
describe('velocitr', function(){
it('should cap the velocity', function(){
var v = new Velocitr();
v.set(30);
assert(v.velocity).equals(30);
v.set(100);
assert(v.velocity).equals(40);
v.set(-100);
assert(v.velocity).equals(-40);
});
it('should create positive velocity when moved forward', function(){
var v = new Velocitr();
v.move(30);
assert(v.velocity).equals(30);
v.move(-30, true);
v.move(-10);
assert(v.velocity).equals(20);
});
it('should be able to chain', function(){
var v = new Velocitr();
v.move(30, true)
.move(60)
.decelerate();
assert(v.velocity).equals(27);
});
});
});
Enjoy
I thought this might be useful for others wanting a similar functionality.