plot-interactive-overlays-attempt2.rkt

#lang racket
;; Updated plot library required, https://github.com/alex-hhh/plot/tree/ah/interactive-overlays
(require plot pict)

;; Helper function to add a pict as a plot overlay -- don't want to add "pict"
;; as a dependency to the "plot" package
(define (add-pict-overlay plot-snip x y pict)
  (send plot-snip add-general-overlay x y
        (lambda (dc x y) (draw-pict pict dc x y))
        (pict-width pict)
        (pict-height pict)))

;; Will be called when the mouse moves over the plot SNIP. X and Y are the
;; mouse position in plot coordinates and they will be #f if the cursor is
;; outside of the actual plot area
(define (on-hover snip event x y)
  (when (and x y)
    ;; ... but only if we are still inside the plot area
    (define sx (sin x))                 ; the function value at X
    (send snip set-overlay-renderers (list (vrule x) (hrule sx)))
    (send snip refresh-overlays)))

;; Create the plot snip and add the hover callback
(define snip (plot-snip (function sin) #:x-min -10 #:x-max 10))
(send snip set-mouse-callback on-hover)

snip

I tried to fix this, but no success yet. Happy to talk more.

I figured it out, the problem was that the plot functions set their own clipping region and have to be passed the correct plot bounds and dc areas. I updated the draw function to use the region received by the snip draw method, see racket/plot#37 for more details. This was not a problem for the original implementation, because I did not change the clipping region in that case.