[texhax] MetaFont Online Display driver

[Daniel H. Luecking]

Igor Liferenko, on Tue, Jun 20, 2017 at 05:45:17 CEST wrote:

>It seems strange to me that using semicolon after "showit" causes
>an extra call to blankrectangle() and updatescreen() functions from
>online display driver.

showit; expands to
  openit; display currentpicture inwindow currentwindow;

I guess both openit and display update the screen.

If the semicolon is omitted, MF does not yet know what
window the display command is supposed to display in.
There could something on the next line that continues the
command. For example,
  display currentpicture inwindow currentwindow
   - 1;

And so MF is not executing display, but waiting for more input.
If you supply a semicolon at the * prompt, I bet you would see
another updatescreen.

Cheers,
Dan

Daniel H. Luecking, Graduate Coordinator
Dept. of Mathematical Sciences
University of Arkansas
Fayetteville, AR, USA

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