PostScript atan error

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PostScript atan error

Postby TedWalther » Wed Jul 12, 2017 6:08 am

Hi. On macOS Sierra, I am using postscript.lsp (newlisp 10.7.0)

In the function drawto, there is a line
Code: Select all
  newy ypos sub newx xpos sub atan neg 90 add /orient exch def


So I generate my postscript instructions with ps:render. Then it comes time to convert the postscript file to a PDF so I can view it, and sometimes it gives an error, other times it doesn't. I make minor tweaks to my output code and the error goes away. But when the error is there, it stays until I change the code, but I never figured out what change I made to avoid the error.

But anyways, I can read postscript a little, but that line doesn't make sense to me. Why is it in there? When I hand edit the postscript file to comment out that line, I can create the PDF without problem.

Sample code that shows the error:

Code: Select all
(define pi (mul 4 (atan 1)))
(define (rad d) (mul d (div pi 180)))
(define (deg r) (mul r (div 180 pi)))

(module "postscript.lsp")

;; I work in inches as my base unit (72 points per inch), but scale things down
;; by scalefactor so they fit on a regular sheet of paper.

(define scalefactor 4)
(ps:scale (div 72 scalefactor) (div 72 scalefactor))

(define ¼ 0.25)
(define ½ 0.5)
(define origx (mul ½ 8.5 scalefactor))
(define origy (mul ½ 11 scalefactor))
(define my-goto (lambda (x y) (ps:goto (add x origx) (add y origy))))
(define my-drawto (lambda (x y) (ps:drawto (add x origx) (add y origy))))

;; https://math.stackexchange.com/questions/76099/polar-form-of-a-superellipse
;; answered Oct 26 2011 at 17:03 by Ross Millikan
;; polar coordinate form of a superellipse
;; r = ab/(|b cos theta|^n + |a sin theta|^n)^(1/n)
;; a is half the height
;; b is half the width
;; n is the exponent of the superellipse
(define super-ellipse-radius (lambda (a b n theta)
  (div (mul a b)
       (pow (add (pow (abs (mul b (cos theta))) n)
                 (pow (abs (mul a (sin theta))) n))
            (div n)))))

(define draw-super-ellipse (lambda (a b n)
  (letn (anglestep (rad 0.1)
         ab (mul a b)
         startr (super-ellipse-radius a b n 0)
         startx (mul startr (cos 0))
         starty (mul startr (sin 0)))
    (my-goto startx starty)
    (for (theta anglestep (mul 2 pi) anglestep)
      (let (r (super-ellipse-radius a b n theta))
        (my-drawto (mul r (cos theta)) (mul r (sin theta)))))
    (my-drawto startx starty))))

(draw-super-ellipse (mul 7 (sqrt 2)) 7 2.718)

(ps:render "standing-desk2.ps")
(! "pstopdf standing-desk2.ps")

(exit)



And here is the error when trying to open the file (macOS auto-converts it to PDF, and pstopdf also has this error:

Code: Select all
%%[ Error: undefinedresult; OffendingCommand: atan; ErrorInfo: CharOffsets %%[ Flushing: rest of job (to end-of-file) will be ignored ]%%
%%[ Warning: PostScript error. No PDF file produced. ] %%
pstopdf failed on file standing-desk2.ps with error code -31000
Cavemen in bearskins invaded the ivory towers of Artificial Intelligence. Nine months later, they left with a baby named newLISP. The women of the ivory towers wept and wailed. "Abomination!" they cried.
TedWalther
 
Posts: 602
Joined: Mon Feb 05, 2007 1:04 am
Location: Abbotsford, BC

Re: PostScript atan error

Postby TedWalther » Wed Jul 12, 2017 6:10 am

I think I found the error. The "atan" is bombing out when drawto is called from a point, to the identical point. So I changed my code a little to guarantee drawto isn't called when the start and end points are identical. Now it works.
Cavemen in bearskins invaded the ivory towers of Artificial Intelligence. Nine months later, they left with a baby named newLISP. The women of the ivory towers wept and wailed. "Abomination!" they cried.
TedWalther
 
Posts: 602
Joined: Mon Feb 05, 2007 1:04 am
Location: Abbotsford, BC

Re: PostScript atan error

Postby georgecraft » Fri Sep 07, 2018 9:43 am

Hi! I am glad you were able to include and outline all these features. They are necessary to consider for the beginners, like I am!
georgecraft
 
Posts: 1
Joined: Fri Sep 07, 2018 9:41 am


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