Re: [TCLCORE] is there a 16-bit limit on canvas coordinates?

[Paul M. <pa...@sa...>]

dr...@hw... writes:

> Paul Mackerras <pa...@sa...> wrote:
> > 
> > Is it possible that line segments that are more than 32768 (or 65536)
> > pixels high could cause a problem?
> > 
> 
> There is code in place that is suppose to handle this.
> (Specifically the TkCanvTranslatePath() routine in tkCanvUtil.c.)
> And as far as anybody knows, it works.  But we are suggesting
> that perhaps you have found a bug.  To fix it, though, we really
> need to catch it in the act of failing....

I finally got around to capturing and reducing an example where it
fails.  If you run the script below, it will create a window showing a
canvas that should have just a single line running from top to bottom.
However, in addition to the real line, it also displays a straight
vertical line starting at the top of the canvas.

I tried varying the last y coordinate.  On a Linux/ppc64 machine with
tk8.5a2, it fails for 29419.5 but not for anything less (even
29419.499999).  On a Linux/x86 machine with tk8.4, the threshold was
29648.5.  Interesting that it isn't 32768...

Also, I just checked that it fails with current CVS.

Paul.

#!/bin/sh
# -*- tcl -*- \
exec wish "$0" -- "$@"

scrollbar .s -command ".c yview" -highlightthickness 0
pack .s -side right -fill y
canvas .c -width 200 -height 350 -bg white -bd 0 \
	-yscrollincr 15 -yscrollcommand ".s set"
pack .c -side top -fill both -expand 1
bind .c <ButtonRelease-4> ".c yview scroll -5 units"
bind .c <ButtonRelease-5> ".c yview scroll 5 units"
bind . q {destroy .}

.c create line {25.5 280.5 40.5 295.5 55.5 310.5 55.5 325.5
    70.5 340.5 70.5 1780.5 85.5 1795.5 85.5 1825.5 100.5 1840.5
    115.5 1855.5 115.5 2050.5 130.5 2065.5 130.5 2425.5
    115.5 2440.5 115.5 2635.5 100.5 2650.5
    100.5 29980} -width 2 -fill red

.c conf -scrollregion {0 0 0 30000}