Arjen Markus Drawing programs often have a scale on top and to the right to indicate the position of the cursor. I thought it would be nice to explore how to do that in Tcl. The script below is very rudimentary, but it shows the principle.
package require Tk
canvas .c -background white
pack .c -fill both
bind .c <Motion> {movePointer %x %y}
.c create line 10 10 10 20 -fill red -width 3 -tags pointerx
.c create line 10 10 20 10 -fill blue -width 3 -tags pointery
proc movePointer {xcrd ycrd} {
.c coords pointerx $xcrd 10 $xcrd 20
.c coords pointery 10 $ycrd 20 $ycrd
}