+(define*-public (stencil-whiteout
+ stil #:optional (thickness 0.3) (color white)
+ (angle-increments 16) (radial-increments 1))
+ "This function works by creating a series of white or @var{color}
+stencils radially offset from the original stencil with angles from
+0 to 2*pi, at an increment of @code{angle-inc}, and with radii
+from @code{radial-inc} to @var{thickness}. @var{thickness} is how big
+the white outline is in staff-spaces. @var{radial-increments} is how
+many copies of the white stencil we make on our way out to thickness.
+@var{angle-increments} is how many copies of the white stencil
+we make between 0 and 2*pi."
+ (if (or (not (positive? angle-increments))
+ (not (positive? radial-increments)))
+ (begin
+ (ly:warning "Both angle-increments and radial-increments must be positive numbers.")
+ stil)
+ (let* ((2pi 6.283185307)
+ (angle-inc (/ 2pi angle-increments))
+ (radial-inc (/ thickness radial-increments)))
+
+ (define (circle-plot ang dec radius original-stil new-stil)
+ ;; ang (angle) and dec (decrement) are in radians, not degrees
+ (if (<= ang 0)
+ new-stil
+ (circle-plot (- ang dec) dec radius original-stil
+ (ly:stencil-add
+ new-stil
+ (ly:stencil-translate original-stil
+ (cons
+ (* radius (cos ang))
+ (* radius (sin ang))))))))
+
+ (define (radial-plot radius original-stil new-stil)
+ (if (<= radius 0)
+ new-stil
+ (ly:stencil-add new-stil
+ (radial-plot
+ (- radius radial-inc)
+ original-stil
+ (circle-plot 2pi angle-inc
+ radius original-stil empty-stencil)))))
+
+ (let ((whiteout-expr
+ (ly:stencil-expr
+ (stencil-with-color
+ (radial-plot thickness stil empty-stencil)
+ color))))
+ (ly:stencil-add
+ (ly:make-stencil
+ `(delay-stencil-evaluation ,(delay whiteout-expr)))
+ stil)))))
+
+(define*-public (stencil-whiteout-box stencil
+ #:optional (thickness 0) (blot 0) (color white))
+ "@var{thickness} is how far in staff-spaces the white outline
+extends past the extents of @var{stencil}."