[NTG-context] graphics

Mikael P. Sundqvist mickep at gmail.com
Fri Dec 7 09:06:03 CET 2018

On Tue, Dec 4, 2018 at 6:03 PM Hans Hagen <j.hagen at xs4all.nl> wrote:
> Hi,
> As most mechanism are reasonable okay now we can look into what future
> versions of ConteXt should provide in terms of functionality. The
> (luatex) engine is also more of less finished or at least stable in
> terms of functionality.
> One possible area of further development is graphics so I'd like to know
> if there are (reasonable) demands for more graphics support using
> metapost. Alan and I are on-and-off working on some extensions and one
> of the things we discuss is visualization of data. The question is of
> course what should be done in the lua/mp/tex combination and what
> externally but the combination has some advantages. There has been
> presentations and discussions at the last meeting and graphics is always
> a nice topic, and also kind of rewarding in terms of development.
> Of course other demands can be formulated too, but these then need to
> come with well defined descriptions (or mockup examples).
> Hans
> -----------------------------------------------------------------
>                                            Hans Hagen | PRAGMA ADE
>                Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
>         tel: 038 477 53 69 | www.pragma-ade.nl | www.pragma-pod.nl
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I don't know if what I describe below is along the lines you ask for,
but here comes two wishes:

1) Full support for drawing implicit curve plots. For some curves,
like a lemniscate
(https://en.wikipedia.org/wiki/Lemniscate_of_Bernoulli) one can easily
succeed by using a parametrisation, but sometimes one end up with
equations and to find a parametrisation might be difficult (not to say
impossible). I asked about this a while ago and got a simple solution
working for that curve, but I think a general working solution would
be neat. I think the bernoulli lemniscate could be a good test curve,
since it intersect itself.

2) Support for transforming images in a more general way. With the
zscaled, slanted, ... we are able to transform any object in an affine
way. It would be nice to be able to transform any object in a more
general way (i.e. by a mapping defined by the user). The example code
below shows what happens in the complex plane with a grid and a curve
when the mapping z to z^2 is applied. Perhaps I am missing something,
but I'm not able to apply this to a piece of text for example, or to
apply it directly to a picture. Instead, I have to loop over all
separate paths. I think the ideal would be to have a "ftransformed"
(or with some other name), and then just define a function (as fun in
the example below), and then be able to do "draw X ftransformed fun;",
where X is some(any?) general object. Is that doable?


%%% Example code

def fun(expr x,y) = (x**2-y**2,2*x*y) enddef;

def sq(expr kv,s) =
fun(xpart point 0 along kv,ypart point 0 along kv)
  for i=s step s until 1: -- fun(xpart point i along kv,ypart point i
along kv) endfor

path rp;
rp = (0,-0.8)..(0.7,-0.2)..(0.7,0.6){dir
150}..(-0.7,0.4)..(-0.4,-0.5){dir 0}..cycle;

% Draw the original grid and the path
for i = -1 step 1/10 until 1+eps:
 for j = -1 step 1/10 until 1+eps:
  draw ((i,-1)--(i,1)) scaled u;
  draw ((-1,j)--(1,j)) scaled u;

draw rp scaled u withcolor darkred withpen pencircle scaled 2bp;

% Draw the grid and curve after map z->z^2
draw image(
for i = -1 step 1/10 until 1+eps:
 for j = 0 step 1/10 until 1+eps:
  draw (sq(((i,0)--(i,1)),1/100)) scaled u;
  draw (sq(((-1,j)--(1,j)),1/100)) scaled u;
draw (sq(rp,1/100)) scaled u withcolor darkred withpen pencircle scaled 2bp;
) xshifted 2.5u;


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