Add a new primitive: linear-transform-graphics

[monaqa]

(graphics version of #218.)

This PR adds a new primitive
linear-transform-graphics: float -> float -> float -> float -> graphics -> graphics.
gr-origin |> linear-transform-graphics a b c d is evaluated to a graphics value into which the gr-origin is transformed with the following formula:

Combining linear-transform-graphics with shift-graphics, you can implement any graphics-to-graphics affine transform (rotation, scaling, reflection, etc.).

This PR also provides two functions, rotate-graphics and scale-graphics, in gr package.

There are two differences between linear-transform-path and linear-transform-graphics:

• linear-transform-graphics can transform any inline-boxes using draw-text primitive.
• When you transform a stroke with linear-transform-graphics command, the stroke thickness is changed (unless a congruence transformation).

[monaqa]

Code example:

@require: stdjareport
@require: gr

let-inline ctx \test deg =
  let width = 1cm in
  let height = 3cm in
  inline-graphics width height 0pt (fun ((x, y) as pt) -> (
    let path = Gr.polygon pt [(x +' width, y); (x +' width, y +' height)] in
    let center = (x +' width *' 0.5, y +' height *' 0.5) in
    [
      stroke 0.5pt Color.black path;
      stroke 1pt Color.red path |> Gr.rotate-graphics center deg;
    ]
  ))
in

document (|
  title = {Linear Transformation of graphics};
  author = {\@monaqa};
  show-title = true;
  show-toc = false;
|) '<
  +p{
    ${30^\circ}: \test(30.0);
  }
  +p{
    ${60^\circ}: \test(60.0);
  }
  +p{
    ${120^\circ}: \test(120.0);
  }
  +p{
    ${300^\circ}: \test(300.0);
  }
>

Result:

(Since rotation is part of the congruent transformation, the result appears to be the same as when using linear-transform-path.)

[monaqa]

I forgot to mention this change: https://github.com/gfngfn/SATySFi/pull/241/files#diff-ff6ba46343bcea35973ad4d439f43e94L217-R261

In the previous code, the coordinates specified by the cm command are applied to all subsequent text (because the cm command precedes the q command). So I switched the order of the two commands.
Since the cm command currently performs only identity transformation, discarding this changes will not cause any problems.

[gfngfn]

Looks very well-written, and I confirmed that the modified implementation indeed works as expected! (especially the composition of transformations and the rotation of texts)

@require: stdjareport
@require: gr

let-inline ctx \test deg =
  let width = 1cm in
  let height = 3cm in
  inline-graphics width height 0pt (fun ((x, y) as pt) -> (
    let path = Gr.polygon pt [(x +' width, y); (x +' width, y +' height)] in
    let center = (x +' width *' 0.5, y +' height *' 0.5) in
    let gr-text = draw-text (x, y) (read-inline ctx {あいう}) in
    [
      stroke 0.5pt Color.black path;
      stroke 1pt Color.red path |> Gr.rotate-graphics center deg;
      stroke 1pt Color.blue path |> Gr.rotate-graphics center deg |> Gr.rotate-graphics center deg;
      gr-text;
      gr-text |> Gr.rotate-graphics center deg;
      gr-text |> Gr.rotate-graphics center deg |> Gr.rotate-graphics center deg;
    ]
  ))
in

document (|
  title = {Linear Transformation of graphics};
  author = {\@monaqa};
  show-title = true;
  show-toc = false;
|) '<
  +p{${30^\circ}: \test(30.0);}
  +p{${60^\circ}: \test(60.0);}
  +p{${120^\circ}: \test(120.0);}
  +p{${300^\circ}: \test(300.0);}
>

Thank you so much for enhancement!