Re: Drawing boxes around grobs

[Aaron Hill]

On 2020-02-08 1:36 pm, Thomas Morley wrote:
> #(define (box-stencil stencil thickness padding color)
>   "Add a box around @var{stencil}, producing a new stencil."
>   (let* ((x-ext (interval-widen (ly:stencil-extent stencil 0) padding))
>          (y-ext (interval-widen (ly:stencil-extent stencil 1) padding))
>          (y-rule
>            (stencil-with-color
>              (make-filled-box-stencil (cons 0 thickness) y-ext) color))
>          (x-rule
>            (stencil-with-color
>              (make-filled-box-stencil
>                   (interval-widen x-ext thickness) (cons 0 thickness)) 
> color)))
>     (set! stencil (ly:stencil-combine-at-edge stencil X 1 y-rule 
> padding))
>     (set! stencil (ly:stencil-combine-at-edge stencil X -1 y-rule 
> padding))
>     (set! stencil (ly:stencil-combine-at-edge stencil Y 1 x-rule 0.0))
>     (set! stencil (ly:stencil-combine-at-edge stencil Y -1 x-rule 0.0))
>     stencil))

You can restore the behavior of things like stem attachment by 
outputting the modified stencil with the original extents:

%%%%
#(define (box-stencil stencil thickness padding color)
  "Add a box around @var{stencil}, producing a new stencil."
  (let* ((x-ext-orig (ly:stencil-extent stencil X))
         (y-ext-orig (ly:stencil-extent stencil Y))
         (x-ext (interval-widen x-ext-orig padding))
         (y-ext (interval-widen y-ext-orig padding))
         (y-rule
           (stencil-with-color
             (make-filled-box-stencil (cons 0 thickness) y-ext) color))
         (x-rule
           (stencil-with-color
             (make-filled-box-stencil
                  (interval-widen x-ext thickness) (cons 0 thickness)) 
color)))
    (set! stencil (ly:stencil-combine-at-edge stencil X 1 y-rule 
padding))
    (set! stencil (ly:stencil-combine-at-edge stencil X -1 y-rule 
padding))
    (set! stencil (ly:stencil-combine-at-edge stencil Y 1 x-rule 0.0))
    (set! stencil (ly:stencil-combine-at-edge stencil Y -1 x-rule 0.0))
    (ly:make-stencil (ly:stencil-expr stencil) x-ext-orig y-ext-orig)))
%%%%

Users of the function might want to choose between using the original 
dimensions and the larger ones, so an additional parameter would 
probably be necessary.


-- Aaron Hill