Re: Centering a stencil on another stencil

[Paul Morris]

> On Aug 11, 2015, at 8:23 PM, Thomas Morley <address@hidden> wrote:
>> 
>> I'm still not happy with the example, because the second stencil, the
>> circle, is centered already.

Ah, right, so your two squares example is better than the circle one.  Lets use 
it for the LSR snippet.

>> As a thought I extended the coding to get the possibility of a
>> centered stencil in both directions in one go:

Makes sense, although I think I’d prefer two separate functions (see below), 
following the pattern of ly:stencil-translate and ly:stencil-translate-axis. 
For one thing that prevents someone from trying (center-stencil-on-stencil #f 
square circle) with your combined function, with an invalid argument of #f.

%%%%%%%%%%%%%%%%%%%%%%%%%

\version "2.19.22"

#(define (center-stencil-on-stencil-axis axis stil-a stil-b)
   "Return a copy of stencil @var{stil-b} that has been
   moved so it is centered on stencil @var{stil-a} on
   @var{axis}. @var{axis} is 0 for X axis, 1 for Y axis."
   (ly:stencil-translate-axis
    (ly:stencil-aligned-to stil-b axis CENTER)
    (interval-center (ly:stencil-extent stil-a axis))
    axis))

% one way:

#(define (center-stencil-on-stencil stil-a stil-b)
   "Return a copy of stencil @var{stil-b} that has been
   moved so it is centered on stencil @var{stil-a} on
   both X and Y axes."
   (center-stencil-on-stencil-axis Y stil-a
     (center-stencil-on-stencil-axis X stil-a stil-b)))

% but your way is probably better:

#(define (center-stencil-on-stencil stil-a stil-b)
   "Return a copy of stencil @var{stil-b} that has been
   moved so it is centered on stencil @var{stil-a} on
   both X and Y axes."
   (ly:stencil-translate
    (centered-stencil stil-b)
    (cons
     (interval-center (ly:stencil-extent stil-a X))
     (interval-center (ly:stencil-extent stil-a Y)))))

test =
#(define-scheme-function (parser location stil-1 stil-2)
   (ly:stencil? ly:stencil?)
   #{
     \markup
     \override #'(word-space . 3)
     \line {
       \stencil #(ly:stencil-add stil-1 stil-2)
       \stencil #(ly:stencil-add stil-1
                   (center-stencil-on-stencil-axis X stil-1 stil-2))
       \stencil #(ly:stencil-add stil-1
                   (center-stencil-on-stencil-axis Y stil-1 stil-2))
       \stencil #(ly:stencil-add stil-1
                   (center-stencil-on-stencil stil-1 stil-2))
     }
   #})

square =
#(make-connected-path-stencil
  '((0 0) (4 0) (4 4) (0 4) (0 0))
  0.4 1 1 #f #f)

green-square =
#(stencil-with-color (make-filled-box-stencil '(0 . 2) '(0 . 2)) green)

circle =
#(stencil-with-color (make-circle-stencil 1 0.3 #f) green)

\test #square #circle
\test #square #green-square

%%%%%%%%%%%%%%%%%%%%%%%%%


I don’t think we need both circle and square examples in the LSR snippet. 
In that case we can simplify by not including the test function?
Either way \override #'(word-space . 3) is a nice improvement.
Let me know what you think and I’ll update the LSR snippet.

Cheers,
-Paul