posting by Roger E Critchlow on Aug 17, 1999 --Create a window, $w, with an analog dial of $diameter pixels, background color $bg, foreground color $fg, and middleground color $mg. The dial will update the frequency stored in the global named $var between minimum value $min and maximum value $max. Grab the dial anywhere with the left mouse button and spin, the marker that spins is only there to give you some rotational feedback. The concentric regions marked on the dial give different update speeds depending on which region you grab with the mouse. The mouse is tracked anywhere on the screen as long as the button remains depressed, so you can get nice fine adjustments by pulling the mouse way outside the dial. proc dial {w var min max diameter bg fg mg} {
# create the dial canvas
canvas $w -width $diameter -height $diameter -bg $bg \
-highlightthickness 0
# create a data array
upvar \#0 $w data
# cleanup the data array
bind $w <Destroy> [list unset $w]
# save arguments
foreach v {w var min max diameter bg fg mg} {
set data($v) [set $v]
}
# compute some values
set data(x0) [expr {$diameter/2}]
set data(y0) [expr {$diameter/2}]
set data(r0) [expr {($diameter-10)/2}]
set data(dr) [expr {$data(r0)/5}]
set data(mark-theta) 250
set data(2pi) [expr {2*atan2(0,-1)}]
# create the dial disk
$w create oval 5 5 [expr {$diameter-5}] [expr {$diameter-5}] \
-fill $fg -outline $mg -width 4 \
-tags dial
# mark the resolution radii with concentric circles
foreach d {2 3 4} {
set r [expr {$d*$data(dr)}]
$w create oval \
[expr {$data(x0)-$r}] [expr {$data(y0)-$r}] \
[expr {$data(x0)+$r}] [expr {$data(y0)+$r}] \
-fill {} -outline $mg -width 4 \
-tags dial
}
# draw a rotating marker
$w create line $data(x0) $data(y0) $data(x0) 5 \
-width 4 -fill $mg -arrow last \
-tags {dial mark}
# press binding
$w bind dial <ButtonPress-1> {dial-press %W %x %y}
# motion binding
$w bind dial <B1-Motion> {dial-motion %W %x %y}
# return our window
return $w
}
proc dial-press {w x y} {
# bind to data array
upvar \#0 $w data
# determine radius and theta
set x [expr {$x-$data(x0)}]
set y [expr {$data(y0)-$y}]
set data(r) [expr {sqrt($x*$x+$y*$y)}]
set data(theta) [expr {int(1000*atan2($y,$x)/$data(2pi))}]
# compute frequency update for this radius
# this assumes the 1000 counts/rev done below
switch [expr {int(($data(r0)-$data(r))/$data(dr))}] {
0 {
set data(kHz/count) 0.01; # 10 kHz/rev
}
1 {
set data(kHz/count) 0.1; # 100 kHz/rev
}
2 {
set data(kHz/count) 1; # 1 MHz/rev
}
default {
set data(kHz/count) 10; # 10 MHz/rev
}
}
}
proc dial-motion {w x y} {
# bind to data array
upvar \#0 $w data
# compute dtheta
set x [expr {$x-$data(x0)}]
set y [expr {$data(y0)-$y}]
set dtheta [expr {(int(1000*atan2($y,$x)/$data(2pi))-$data(theta))%1000}]
if {$dtheta > 500} { set dtheta [expr {$dtheta-1000}] }
# update theta
set data(theta) [expr {($data(theta)+$dtheta)%1000}]
# update marker
set data(mark-theta) [expr {$data(mark-theta)+$dtheta}]
set t [expr {$data(2pi)*$data(mark-theta)/1000}]
$w coords mark $data(x0) $data(y0) \
[expr {$data(r0)*cos($t)+$data(x0)}] \
[expr {$data(y0)-$data(r0)*sin($t)}]
# update frequency
upvar \#0 $data(var) frequency
set f [expr {$frequency-$dtheta*$data(kHz/count)}]
if {$f < $data(min)} {
set f $data(min)
} elseif {$f > $data(max)} {
set f $data(max)
}
# update frequency variable
set frequency [format %12.2f $f]
}
# Here's some demo code:
set bg \#4f4f4f
set fg grey
set mg white
set frequency 15000.00
. configure -bg $bg
pack [frame .f -bg $bg] -side top -fill x
pack [label .f.l -font {-size 32} -width 9 -anchor e \
-textvar frequency -bg $bg -fg $mg] -side left
pack [label .f.hz -font {-size 32} -text "kHz" -bg $bg -fg $mg] -side left
pack [dial .d frequency 0.00 30000.0 200 $bg $fg $mg] -side topuniquename 2014jan27For those who do not have the facilities or time to implement the code above, here is an image of the dial and needle that are drawn on a Tk 'canvas' --- which is packed below a 'frame' widget containing a couple of 'label' widgets.
