🚀 go-pugleaf

This is my first attempt at writing a mouse-tracker.  I'm not sure whether I'm
doing things in the best way, so if you could comment/correct I'd be grateful.
--Hans

This is for e/lisp code.
I want to highlight the following list structure whenever the mouse is over a
left parenthesis.  I just want to look at the mouse motion event, and then pass
it on to the next motion event handler on the stack.
Questions:
	- How to pass on to the next event handler?  I kludged this below, but
	is this the best way?
	- This is expensive code to run, tracking the mouse all the time.  Any
	way to speed it up?
	- Should I be using drag zones for the highlighting?

--------------------snip, snip------------------------------------------------

(defvar running-epoch (boundp 'epoch::version))
;;; mouse-tracking:  live action following the mouse
;;; --------------
;;; highlights a list if looking-at one.  Does _not_ copy it into kill buffer
;;; until you mouse-left.
;;;
;;; mousing is defined in the epoch manual, "Mouse Events"

(require 'motion)

(defvar mouse-tracker-drag-zone nil)

;;; the motion event handler:  if over a list in a lisp-mode buffer, hilite.
(defun mouse-tracker (type value screen)
  (let ((epoch::event-handler-abort nil)
	)
    (save-excursion
      (save-window-excursion
	(let ((point (coords-to-point (elt value 0)(elt value 1) (current-screen))))
	  (when point
		(mouse::set-point point)
		(when ;; am I interested in event?
		 (or (equal mode-name "Emacs-Lisp")
		     (equal mode-name "Lisp"))
		      (if (looking-at "(")
			  (progn
			    (call-interactively 'set-mark-command)
			    (condition-case nil 
				(forward-sexp)
			      (error ))
			    (when mouse-tracker-drag-zone
				  (delete-zone mouse-tracker-drag-zone))
			    (setq mouse-tracker-drag-zone (add-zone (point) (mark)
								    motion::style)))
			(when mouse-tracker-drag-zone
			      (delete-zone mouse-tracker-drag-zone)))
		      )
		))))
    
    ;; and pass on event to next handler
    (let* ((myself (pop-event 'motion))
	   (next-handler (pop-event 'motion)))
      (push-event 'motion next-handler)
      (funcall next-handler type value screen)
      (push-event 'motion myself))
    
    ;; keep feeding myself fresh events
    (epoch::query-pointer) 
    
    ))

(defun add-mouse-tracker-handler ()
  (push-event 'motion 'mouse-tracker))

(defun remove-mouse-tracker-handler ()
  "be careful!  must follow previous push-event!"
  (pop-event 'motion))

(when running-epoch
      (add-mouse-tracker-handler))