Gerhard Reithofer 2010-05-24 - Years ago I've seen an implementation of dials on a SGI workstation, which was very easy to use, because it is not necessary to target as exact as for hand based dials.
Also simple linear mouse movements can be used instead of circular ones.<<br>>
Shift- or Ctrl-key to control the dial sensitivity of the mouse movement.<<br>>
!!!!!!
[Another (rotated) dials widget]
!!!!!!
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======
 #
 # rdial.tcl
 #
 # Contents: a "rotated" dial widget or thumbnail "roller" dial
 # Date: Son May 23, 2010
 #
 # Abstract
 #   A mouse dragable "dial" widget from the side view - visible
 #   is the knurled area - Shift & Ctrl changes the sensitivity 
 #
 # Copyright (c) Gerhard Reithofer, Tech-EDV 2010-05
 #
 # The author  hereby grant permission to use,  copy, modify, distribute,
 # and  license this  software  and its  documentation  for any  purpose,
 # provided that  existing copyright notices  are retained in  all copies
 # and that  this notice  is included verbatim  in any  distributions. No
 # written agreement, license, or royalty  fee is required for any of the
 # authorized uses.  Modifications to this software may be copyrighted by
 # their authors and need not  follow the licensing terms described here,
 # provided that the new terms are clearly indicated on the first page of
 # each file where they apply.
 #
 # IN NO  EVENT SHALL THE AUTHOR  OR DISTRIBUTORS BE LIABLE  TO ANY PARTY
 # FOR  DIRECT, INDIRECT, SPECIAL,  INCIDENTAL, OR  CONSEQUENTIAL DAMAGES
 # ARISING OUT  OF THE  USE OF THIS  SOFTWARE, ITS DOCUMENTATION,  OR ANY
 # DERIVATIVES  THEREOF, EVEN  IF THE  AUTHOR  HAVE BEEN  ADVISED OF  THE
 # POSSIBILITY OF SUCH DAMAGE.
 #
 # THE  AUTHOR  AND DISTRIBUTORS  SPECIFICALLY  DISCLAIM ANY  WARRANTIES,
 # INCLUDING,   BUT   NOT  LIMITED   TO,   THE   IMPLIED  WARRANTIES   OF
 # MERCHANTABILITY,    FITNESS   FOR    A    PARTICULAR   PURPOSE,    AND
 # NON-INFRINGEMENT.  THIS  SOFTWARE IS PROVIDED  ON AN "AS  IS" BASIS,
 # AND  THE  AUTHOR  AND  DISTRIBUTORS  HAVE  NO  OBLIGATION  TO  PROVIDE
 # MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
 #
 # Syntax:
 #   rdial::create w ?-width wid? ?-height hgt?  ?-value floatval?
 #        ?-bg|-background bcol? ?-fg|-foreground fcol? ?-step step?
 #        ?-slow sfact? ?-fast ffact? ?-orient horizontal|vertical?
 #
 
 # using {*}, can be replaced by eval
 package require Tk 8.5
 
 namespace eval rdial {
    variable d2r
    variable canv
    variable sfact
    variable ssize
    variable sector 88
    variable ovalue
    variable callback ""

    # a few constants to reduce expr
    set d2r [expr {atan(1.0)/45.0}]
    set ssize [expr {sin($sector*$d2r)}]

    # widget default values  
    array set def {
        background "#dfdfdf"
        foreground "black"
        orient horizontal callback ""
        width 80 height  8
        step  10 value 0.0
        slow 0.1 fast 10
    }

    proc err_out {err {msg ""}} {
        if {$msg eq ""} {
            set msg "must be -bg, -background, -fg, -foreground,\
                    -width, -height, -value, -slow, -fast -orient or -step"
        }
        error "$err: $msg"
    }

    # configure method - writeonly
    proc configure {w nopt val args} {
        variable opt
        variable canv
        variable ssize
        variable sfact

        if {[llength $args]%2} {
            err_out "invalid syntax" \
                    "must be \"configure opt arg ?opt arg? ...\""
        }

        set args [linsert $args 0 $nopt $val]
        foreach {o arg} $args {
            if {[string index $o 0] ne "-"} {
                err_out "invalid option \"$nopt\""
            }
            switch -- $o {
                "-bg" {set o "-background"}
                "-fg" {set o "-foreground"}
            }
            set okey [string range $o 1 end]
            if {[info exists opt($okey,$w)]<0} {
                err_out "unknown option \"$o\""
            }
            if {$o eq "-width" || $o eq "-height"} {
                $canv($w) configure $o $arg
            }
            set opt($okey,$w) $arg
            if {$o eq "-width"} {
                set sfact($w) [expr {$ssize*2/$opt(width,$w)}]
            }
        }
        draw $w $opt(value,$w)
    }

    # cget method
    proc cget {w nopt} {
        variable opt
        switch -- $nopt {
            "-bg" {set nopt "-background"}
            "-fg" {set nopt "-foreground"}
        }
        set okey [string range $nopt 1 end]
        if {[info exists opt($okey,$w)]<0 &&
            [string index $nopt 0] ne "-"} {
            err_out "unknown option \"$nopt\""
        }
        return $opt($okey,$w)
    }

    # draw the thumb wheel view
    proc draw {w val} {
        variable opt
        variable d2r
        variable canv
        variable ssize
        variable sfact
        variable sector

        # every value is maped to the visible sector
        set mod [expr {$val-$sector*int($val/$sector)}]

        set stp $opt(step,$w)
        set wid $opt(width,$w)
        set hgt $opt(height,$w)
        set dfg $opt(foreground,$w)
        set dbg $opt(background,$w)

        $canv($w) delete all
        if {$opt(orient,$w) eq "horizontal"} {
           $canv($w) create rectangle 0 0 $wid $hgt -fill $dbg
            # from normalized value to left end
            for {set ri $mod} {$ri>=-$sector} {set ri [expr {$ri-$stp}]} {
                set offs [expr {($ssize+sin($ri*$d2r))/$sfact($w)}]
                $canv($w) create line $offs 0 $offs $hgt -fill $dfg
            }
            # from normalized value to right end
            for {set ri [expr {$mod+$stp}]} {$ri<=$sector} {set ri [expr {$ri+$stp}]} {
                set offs [expr {($ssize+sin($ri*$d2r))/$sfact($w)}]
                $canv($w) create line $offs 0 $offs $hgt -fill $dfg
            }
        } else {
           $canv($w) create rectangle 0 0 $hgt $wid -fill $dbg
            # from normalized value to upper end
            for {set ri $mod} {$ri>=-$sector} {set ri [expr {$ri-$stp}]} {
                set offs [expr {($ssize+sin($ri*$d2r))/$sfact($w)}]
                $canv($w) create line 0 $offs $hgt $offs -fill $dfg
            }
            # from normalized value to upper end
            for {set ri [expr {$mod+$stp}]} {$ri<=$sector} {set ri [expr {$ri+$stp}]} {
                set offs [expr {($ssize+sin($ri*$d2r))/$sfact($w)}]
                $canv($w) create line 0 $offs $hgt $offs -fill $dfg
            }
        }
        # let's return the widget/canvas  
        set opt(value,$w) $val
    }

    proc drag {w coord {mode 0}} {
        variable opt
        variable ovalue

        # calculate new value
        if {$opt(orient,$w) eq "horizontal"} {
            set diff [expr {$coord-$ovalue($w)}]
        } else  {
            set diff [expr {$ovalue($w)-$coord}]
        }
        if {$mode<0} {
            set diff [expr {$diff*$opt(slow,$w)}]
        } elseif {$mode>0} {
            set diff [expr {$diff*$opt(fast,$w)}]
        } else  {
            set diff [expr {$diff}]
        }
        set opt(value,$w) [expr {$opt(value,$w)+$diff}]

        # call callback if defined...
        if {$opt(callback,$w) ne ""} {
            {*}$opt(callback,$w) $opt(value,$w)
        }

        # draw knob with new angle
        draw $w $opt(value,$w)
        # store "old" value for diff
        set ovalue($w) $coord
    }

    proc create {w args} {
        variable def
        variable d2r
        variable opt
        variable canv
        variable ssize
        variable sfact
        variable sector

        set opt_list [array names def]
        # set default values
        foreach {d} $opt_list {
            set opt($d,$w) $def($d)
        }
        # handle command paramters 
        foreach {tmp arg} $args {
            set o [string range $tmp 1 end]
            switch -- $o {
                "bg" {set o background}
                "fg" {set o foreground}
            }
            if {[lsearch $opt_list $o]<0 ||
                [string index $tmp 0] ne "-"} {
                err_out "bad option \"$o\""
            }
            set opt($o,$w) $arg
        }

        # width specific scale constant
        set sfact($w) [expr {$ssize*2/$opt(width,$w)}]

        # just for laziness ;)
        set nsc [namespace current]
        set wid $opt(width,$w)
        set hgt $opt(height,$w)
        set bgc $opt(background,$w)

        # create canvas and bindings
        if {$opt(orient,$w) eq "horizontal"} {
            set canv($w) [canvas $w -width $wid -height $hgt]
            # standard bindings
            bind $canv($w) <ButtonPress-1> [list set ${nsc}::ovalue(%W) %x]
            bind $canv($w) <B1-Motion>       [list ${nsc}::drag %W %x]
            bind $canv($w) <ButtonRelease-1> [list ${nsc}::drag %W %x]
            # fine movement
            bind $canv($w) <Shift-ButtonPress-1> [list set ${nsc}::ovalue(%W) %x]
            bind $canv($w) <Shift-B1-Motion>       [list ${nsc}::drag %W %x -1]
            bind $canv($w) <Shift-ButtonRelease-1> [list ${nsc}::drag %W %x -1]
            # course movement
            bind $canv($w) <Control-ButtonPress-1> [list set ${nsc}::ovalue(%W) %x]
            bind $canv($w) <Control-B1-Motion>       [list ${nsc}::drag %W %x 1]
            bind $canv($w) <Control-ButtonRelease-1> [list ${nsc}::drag %W %x 1]
        } else {
            set canv($w) [canvas $w -width $hgt -height $wid]
            # standard bindings
            bind $canv($w) <ButtonPress-1> [list set ${nsc}::ovalue(%W) %y]
            bind $canv($w) <B1-Motion>       [list ${nsc}::drag %W %y]
            bind $canv($w) <ButtonRelease-1> [list ${nsc}::drag %W %y]
            # fine movement
            bind $canv($w) <Shift-ButtonPress-1> [list set ${nsc}::ovalue(%W) %y]
            bind $canv($w) <Shift-B1-Motion>       [list ${nsc}::drag %W %y -1]
            bind $canv($w) <Shift-ButtonRelease-1> [list ${nsc}::drag %W %y -1]
            # course movement
            bind $canv($w) <Control-ButtonPress-1> [list set ${nsc}::ovalue(%W) %y]
            bind $canv($w) <Control-B1-Motion>       [list ${nsc}::drag %W %y 1]
            bind $canv($w) <Control-ButtonRelease-1> [list ${nsc}::drag %W %y 1]
        }

        # draw insides
        draw $w $opt(value,$w)
        return $w
    }
 }

 #-------- test & demo
 if {[info script] eq $argv0} {
    array set disp_value {rs -30.0 rh 120.0 rv 10.0}
    proc rndcol {} {
        set col "#"
        for {set i 0} {$i<3} {incr i} {
            append col [format "%02x" [expr {int(rand()*230)+10}]]
        }
        return $col
    }
    proc set_rand_col {} {
        rdial::configure .rs -fg [rndcol] -bg [rndcol]
    }
    proc show_value {which v} {
        set val [rdial::cget .$which -value]
        set ::disp_value($which) [format "%.1f" $val]
        switch -- $which {
            "rh" {
                if {abs($val)<30} return
                rdial::configure .rs -width [expr {abs($val)}]
            }
            "rv" {
                if {abs($val)<5}  return
                rdial::configure .rs -height [expr {abs($val)}]

            }
            "rs" {
                if {!(int($val)%10)} set_rand_col
            }
        }
    }
    label .lb -text "Use mouse button with Shift &\nControl for dragging the dials"
    label .lv -textvariable disp_value(rv)
    rdial::create .rv -callback {show_value rv} -value $disp_value(rv)\
            -width 200 -step 5 -bg blue -fg white
    label .lh -textvariable disp_value(rh)
    rdial::create .rh -callback {show_value rh} -value $disp_value(rh)\
            -width $disp_value(rh) -height 20 -fg blue -bg yellow -orient vertical
    label .ls -textvariable disp_value(rs)
    rdial::create .rs -callback {show_value rs} -width $disp_value(rh) \
            -height $disp_value(rv) -value $disp_value(rh)
    pack {*}[winfo children .]
    wm minsize . 220 300
 }
======

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