[whatwg] canvas 2d's ellipse

Rik Cabanier cabanier at gmail.com
Tue Apr 30 14:20:09 PDT 2013

People on the blink team are starting to implement 'ellipse' [1].
Looking at this API, I have a couple of questions:

1. Why are most of the parameters not optional?
Currently, none of the parameter to ellipse are optional.
So, if you want to draw a simple circle, you have to supply 8 parameters,
even though only 3 are needed.
All other calls have anticlockwise optional, why not ellipse?

2. when is an ellipse closed?
It's not clear from the prose if there is ever a 'closepath'. So, if you
have square end caps, you will see a discontinuity unless you call

3. the following lines are somewhat confusing:

If the anticlockwise argument false and endAngle-startAngle is equal to or
greater than 2π, or, if the anticlockwise argument is true
andstartAngle-endAngle is equal to or greater than 2π, then the arc is the
whole circumference of this ellipse.


Since the points are on the ellipse, as opposed to being simply angles from
zero, the arc can never cover an angle greater than 2π radians.

Why not simply say that the angles define the points on the ellips and draw
the arc between them? That seems more clear.


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