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

David Kastrup dak at gnu.org
Tue Jun 27 15:46:50 UTC 2017

Simon Budig <simon at budig.de> writes:

> Hi David.
> I understand that this is kind of a clash of philosophies here, and
> the mathematician in me very much sympathize with you in the sense,
> that exact representations are helpful and important.
> But the computer scientist in me thinks, that sometimes "good enough"
> is good enough...

It wasn't good enough for PostScript, and it wasn't good enough for
METAFONT, and its author Donald Knuth basically _founded_ computer
science as a discipline.  It wasn't good enough for SVG.  CSS is
neutral: you have to specify one of "deg, grad, rad, turn" as unit but
most tutorials will tell you only about "deg".

The "good enough" faction are engineers.  And even they tend to prefer
degrees for angles...

Cairo really is the odd man out in graphics software.  I wasn't really
talking about removing the existing calls, just adding ones working with
degrees and working _exactly_ where multiples of 90 degrees are

And "good enough" doesn't really cut it in graphics software either when
we are talking about line thicknesses.  An epsilon of difference may
easily fatten or thin a line by a whole pixel.  You don't want any
jaggies anywhere when turning by 90 degrees.

David Kastrup

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