Flickering Line (redraw / grread / grdraw)

[dlbsurveysuk]

I found this routine on The Swamp that dynamically draws an irregular polygon (I've removed some extraneous following code, added the pickbox stuff and modified the grdraw line).

When the mouse is moved, the line flickers. I'm assuming this is due to the combination of redraw/grread/grdraw.

Can the code be modified to stop this flickering?

Thanks.

(defun c:DPOLY (/ PT PTLIST SS)

  ; Clone Select CP
  ; by ElpanovEvgeniy
  ; (2006-05-11 11:05:52)
  ; (lst-ent-wp)

(setq OPB (getvar "PICKBOX"))

(setq PTLIST (list (setq PT (getpoint "Specify first point : "))))

(princ "\nSpecify next point : ")
(princ)
(setvar "PICKBOX" 0)

  (while

     (setq PT (progn
                          (while (and (setq PT (grread 5)) (= (car PT) 5))
                                (redraw)

                                (mapcar
                                     (function
                                          (lambda (X1 X2)
                                              (grdraw X1 X2 255 0) ;;; (grdraw x1 x2 6 5) ;;;
                                          )
                                     )
                                  (cons (cadr PT) PTLIST)
                                  (append PTLIST (cdr PT))
                                )
                           )

                        (if (listp (cadr PT))
                            (cadr PT))
      )            )

      (setq PTLIST (cons PT PTLIST))

  )

(redraw)
(setvar "PICKBOX" OPB)
(princ)
)

[ronjonp]

No flicker here. Perhaps it's your video card?

[dlbsurveysuk]

Hmm interesting. I don't get any flickering with anything else. If I perform a polygonal crop of a point cloud, which this routine visually emulates, there is no flicker at all...

[dlbsurveysuk]

I can see if I move the mouse a tiny bit and stop, the line has one fast flicker like it's a slow redraw?

[komondormrex]

also no flickering.

and i would recommend you do not touch system variables. pickbox in that case. you'd better switch off pickbox with grread argument. see correction below.

(defun c:DPOLY (/ PT PTLIST SS)
	; Clone Select CP
	; by ElpanovEvgeniy
	; (2006-05-11 11:05:52)
	; (lst-ent-wp)
	(setq PTLIST (list (setq PT (getpoint "Specify first point : "))))
	(princ "\nSpecify next point : ")
	(princ)
	(while
		(setq PT (progn
		          (while (and (setq PT (grread t 5 0)) (= (car PT) 5))
		                (redraw)
		                (mapcar
		                     (function
		                          (lambda (X1 X2)
		                              (grdraw X1 X2 1 0) ;;; (grdraw x1 x2 6 5) ;;;
		                          )
		                     )
		                  (cons (cadr PT) PTLIST)
		                  (append PTLIST (cdr PT))
		                )
		           )
		           (if (listp (cadr PT))
		                    (cadr PT)
			   )
		      ) 
		)
		(setq PTLIST (cons PT PTLIST))
	)
	(redraw)
	(princ)
)

[komondormrex]

that flickering may also be when grdraw draws slant lines due to pixel approximation.

[Kent1Cooper]

I don't get any flicker, either from your original or @komondormrex 's edited version.  But what is it supposed to do?  I notice it has a localized variable SS that is never set or used.

[Sea-Haven]

Just a comment may be helpful.

Have a client in last few days similar problem, used grread with brand new laptop, LT 2024, the mess of the boxes appearing was a problem, did not want to try to fix his laptop, graphics card or windows problem, so used (command "Rectang" "pause" "pause") then got boundingbox, min, max and erased the box. 

[dlbsurveysuk]

Thanks for the reply. Yes I had considered something along the lines of your idea for a rectangular selection, and also a polyline for a polygonal selection.

I'm hoping to use this routine in another Lisp for cropping point clouds https://forums.autodesk.com/t5/visual-lisp-autolisp-and-general/lisp-to-crop-a-point-cloud-fails-to-... This would mean that sometimes the number of vertices could run into the teens.

The flicker is only slightly annoying and is something I can live with until hopefully a solution presents itself...