snapMode

$canvaseditor snapMode on: manages control-button-1 pointer to snap to nearest dot. Is invoked on move, scale, rotate, and shear action.
$canvaseditor snapMode off: manages control-button-1 to do nothing. Invoked on finish transformation.

obj method canvaseditor snapMode {{onOff on}} {
  set canvas [my canvas]
  if {$onOff} then {
    bind $canvas <<ControlClick>>  [list apply [list {x y} {
      proc pointerXY {} "list $x $y"
    } [namespace current]] %x %y]
    bind $canvas <<ControlClick>> +[list apply [list self {
      set found [$self nearestDot -unselected]
      $self memory found $found
      set foundx [$found cget -x]
      set foundy [$found cget -y]
      #
      set currentBind [bind [my canvas] <Motion>]
      #
      lappend map
      if {[regexp {\[[^\]]+\mcanvasx\M[^\]]+\]} $currentBind cmdx]} then {
        lappend map $cmdx $foundx
      }
      if {[regexp {\[[^\]]+\mcanvasy\M[^\]]+\]} $currentBind cmdy]} then {
        lappend map $cmdy $foundy
      }
      #
      set cmd [string map $map $currentBind]
      eval $cmd
      $self finishTransform
    } [namespace current]] $self]
    bind $canvas <<ShiftControlClick>> [bind $canvas <<ControlClick>>]
    bind $canvas <<ShiftControlClick>> +[list apply {
      self {
        $self withUndo connectWarpedLineToDot [$self memory found]
      }
    } $self]
    bind $canvas <<ControlClick>> +break 
    bind $canvas <<ShiftControlClick>> +break
  } else {
    bind $canvas <<ControlClick>> ""
    bind $canvas <<ShiftControlClick>> ""
  }
}