Transformations

c.translate(0, 0) c.rotate(Math.PI*2/5) c.scale(1.0, 1.0) 

To rotate along origin:

c.translate(ox, oy) c.rotate(theta) c.translate(-ox, -oy) 

To scale along origin:

c.translate(-ox*x, -oy*y) c.scale(x, y) c.translate(ox/x, oy/y) 

See MDN: Transformations.