[cairo] Shouldn't Cairo use/offer degrees rather than radians?

[David Kastrup]

David Kastrup <dak at gnu.org> writes:

> Lawrence D'Oliveiro <ldo at geek-central.gen.nz> writes:
>
>> On Fri, 30 Jun 2017 07:02:36 +0200, David Kastrup wrote:
>>
>>> Lawrence D'Oliveiro <ldo at geek-central.gen.nz> writes:
>>> 
>>>> On Thu, 29 Jun 2017 08:08:04 +0200, David Kastrup wrote:
>>>>  
>>>>> It replaces a sin(x)/cos(x) pair by a sin(x)/sin(pi/2-x) pair.  The
>>>>> largest cumulative effect is at pi/4.  
>>>>
>>>> So you introduce a kink at π/4. How is this any better, again?  
>>> 
>>> There is no kink.  None at all.
>>
>> No kink? Have a look--here’s your kink, at π/4.
>
> I have no idea what you are plotting here.  Your "fake" does not look
> like a _function_ of either axis, and it also doesn't have the symmetry
> of the sin/cos pairing of my code.  So if it is neither a function in
> isolation nor the actual value pair, what is it?
>
> Care to show the program you are generating your plots with?

And show the units it is working with?

Cutting this a bit short: can we actually skip the part where you are
trying to show, using bravado and ad-hoc arguments, to show that I am
incompetent and don't know what I am talking about?

If you are worried about the added jitter due to the _internal_
implementation using the built-in sin/cos with radians as arguments,
I can of course add a post-correction stage (about doubling the
computational cost, of course) that will use the addition theorem in
order to get the full resolution of angles provided by the different
rasterization of degrees and radians.  But that's sort of pointless as
it will add precision amounting to something like 2^-53 .

-- 
David Kastrup