[cairo] Adding cairo_shear and family

[Travis Griggs]

On Jan 11, 2009, at 12:56 PM, M Joonas Pihlaja wrote:

>
> On Sun, 11 Jan 2009, Behdad Esfahbod wrote:
>
>> I think the API is mainly designed to be used with either nonzero  
>> sx or sy,
>> not both.
>
> Sure.  Still, the docs shouldn't say it's doing an x-shear and a
> y-shear at the same time because the operation can't be
> represented as any kind of shearing at all (it doesn't preserve
> area unless one of sx, sy is zero.)
>
>> I like having the exact matrix in there.  We don't do that for
>> rotate, scale, and translate because they are obvious.
>
> During a discussion on #cairo a while back I was told that we
> don't use matrices in the docs because that would nail down a
> specific interpretation for the action of the CTM:  Is it from
> the left on column vectors vs. from the right on row vectors?
> Right now there's no place in the docs that suggests either
> interpretation, so even just saying that cairo_shear() multiplies
> the CTM by some other matrix is ambiguous.
>
>> I don't like the idea of separate calls.
>
> Me neither, but it's no fun having an operation that does
> something else that what it says in the name either. ;)
>
> How about something like
>
>   cairo_shear(cr, angle, scale);
>
> This would shear by the given amount along the axis given as an
> angle from the x-axis.



Hey, I kinda like that. Nice suggestion.

--
Travis Griggs
Objologist
I patented thinking... and I still can't find anyone infringing.