Arjen Markus (22 november 2018) Today I realised that you do not need to put a canvas in a top level window (manage it) to still use it. Ordinarily I do something like:
pack [canvas .c] ... draw graphical objects
But you can simply do:
canvas .c # Draw a line ... .c create line 10 100 200 200 -fill blue -width 5
The canvas may not be visible, but it does contain the line, as you will see if you put it into a top level window or the like:
pack .c
Easy to try in a "wish" console.
At first sight, this does not to be very useful, but it also works with pdf4tcl:
# plotlinpr.tcl --
# Simple plot of linear programming problem
#
package require pdf4tcl
#
# DO NOT pack the canvas, only create it ...
#
#pack [canvas .c -bg white -width 400 -height 300]
canvas .c -bg white -width 400 -height 300
.c create line 50 250 350 250 -width 4
.c create line 50 250 50 50 -width 4
.c create text 200 270 -text "X"
.c create text 30 150 -text "Y" -angle 90
.c create text 150 40 -text "Constraints" -fill blue
.c create line 50 100 350 200 -fill blue
.c create line 150 50 275 250 -fill blue
.c create text 180 170 -text "Optimum" -fill red
.c create line 90 50 332 250 -fill red -width 4
after 1000 {
set pdf1 [::pdf4tcl::new %AUTO% -paper {12.0c 8.0c}]
$pdf1 canvas .c -width 13.4c
$pdf1 write -file linear_programming.pdf
set go 1
}So this trick allows you to produce pictures in the background.