shearMode

$canvaseditor shearmode mode: manages canvas bindings to shear selected objects along arbitrary axis
obj method canvaseditor shearMode {{mode parallel}} {
  set canvas [my canvas]
  $self selected dots storeXY
  $self selected calcCenter
  #
  set axis [$self calcAxis]
  set p0 [$axis firstDot]
  set p1 [$axis lastDot]
  #
  set cx [$p0 cget -x]
  set cy [$p0 cget -y]
  set ex [$p1 cget -x]
  set ey [$p1 cget -y]
  set dx [- $ex $cx]  
  set dy [- $ey $cy]
  set phi [- [atan2 $dx $dy] [atan2 1 0]]
  #
  set nDot [$self nearestDot -selected -end]
  set x0 [$nDot cget -x]
  set y0 [$nDot cget -y]
  #
  $self memory currentDot $nDot
  $self memory transformation "shear diagonal $mode"
  #
  if {[distToLine $cx $cy $ex $ey $x0 $y0] < 1} then {
    return -code error "Too close to axis!"
  }
  #
  set dot [new dot $x0 $y0]
  #
  $self memory before [$self undoRedoCode]
  #
  $self pointerToDot $nDot
  $self memory currentDot $nDot
  $self selected blink off
  $self basicBindings off
  $self statusLine Shear objects diagonal $mode
  $self snapMode on
  $axis dots show
  switch -exact -- $mode {
    horizontal {
      set motionBinding [subst -nocommand {
          $dot configure -x [$self canvasx %x] -y $y0
          $self shearSelection $dot $nDot $cx $cy $phi $mode
        }]
    }
    vertical {
      set motionBinding [subst -nocommand {
          $dot configure -x $x0 -y [$self canvasy %y]
          $self shearSelection $dot $nDot $cx $cy $phi $mode
        }]
    }
    default {
      set motionBinding [subst -nocommand {
          $dot configure -x [$self canvasx %x] -y [$self canvasy %y]
          $self shearSelection $dot $nDot $cx $cy $phi $mode
        }]
    }
  }
  after idle [list bind $canvas <Motion> $motionBinding]
  bind $canvas <<Click>> "
    $self finishTransform
    $dot destroy
    $axis dots show no
    "
}