Plot interactive overlay demo

plot-interactive-overlay-demo.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 x y)
  ;; Clear previous overlays, as we'll set up new ones ...
  (send snip clear-overlays)

  (when (and x y)
    ;; ... but only if we are still inside the plot area
    
    (define sx (sin x))                 ; the function value at X

    ;; Draw a cross line at the current function position, xrule is more
    ;; efficient than drawing both a vrule or a hrule
    (send snip add-xrule-overlay x sx)

    ;; Or we could draw the lines separately...
    ;; (send snip add-vrule-overlay x)
    ;; (send snip add-hrule-overlay sx)

    ;; Add a marker at the current function position, we also provide a label
    ;; with the function value
    (send snip add-mark-overlay x sx #:radius 10 #:label (~r sx #:precision 2))

    ;; Add a picture at the current mouse location
    (define p (vl-append (text (format "X Value ~a" (~r x #:precision 2)))
                         (text (format "Y Value ~a" (~r sx #:precision 2)))))
    (add-pict-overlay snip x y p))

  ;; Finally, refresh the plot
  (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

Another use case for this feature: the two plots are "linked" so that hovering the mouse on one plot will update the "current" line on both of them.

Interactive overlays on a histogram plot