#895 Canvas inconsistantly draws lines on Linux/UNIX

[Brent B. Welch]

OriginalBugID: 4195 Bug
Version: 8.3
SubmitDate: '2000-02-16'
LastModified: '2000-02-16'
Severity: MED
Status: UnAssn
Submitter: ericm
ChangedBy: ericm
OS: Linux-Red Hat

I want to create a line like this in the canvas (# indicates a
colored pixel):

#
#
#
#
#

If I draw it from the bottom to the top, ala

.c create line 50 50 52 48 52 30

It omits one pixel at the top of the diagonal, giving me this:

#
#

#
#

If I draw it from the top, it draws correctly:

.c create line 52 30 52 48 50 50

These two commands should produce visually indistinguishable
lines. The first command should not omit the pixel at the top
of the diagonal.

- eric

[Peter Caffin]

Logged In: YES
user_id=2029956
Originator: NO

Tested with:

########################
pack [canvas .c]
# Broken
.c create line 50 50 52 48 52 30
# Works
.c create line 152 130 152 148 150 150
########################

The only difference being a 1 prepended to all numbers in the second example, to make it easier to view the two side by side in the same canvas.

I can confirm the effect still exists in Tk 8.5.2 (teapot) on Linux. A similar but different effect appears on Windows XP. It doesn't act as expected on either platform. I haven't tested on Mac.