text: import warnings
  from functools import reduce
  from ..Qt import QtGui, QtCore, isQObjectAlive
  from ..GraphicsScene import GraphicsScene
  from ..Point import Point
  from .. import functions as fn
  import weakref
  import operator
  from ..util.lru_cache import LRUCache
  
  
  class GraphicsItem(object):
      """
      **Bases:** :class:`object`
  
      Abstract class providing useful methods to GraphicsObject and GraphicsWidget.
      (This is required because we cannot have multiple inheritance with QObject subclasses.)
  
      A note about Qt's GraphicsView framework:
  
      The GraphicsView system places a lot of emphasis on the notion that the graphics within the scene should be device independent--you should be able to take the same graphics and display them on screens of different resolutions, printers, export to SVG, etc. This is nice in principle, but causes me a lot of headache in practice. It means that I have to circumvent all the device-independent expectations any time I want to operate in pixel coordinates rather than arbitrary scene coordinates. A lot of the code in GraphicsItem is devoted to this task--keeping track of view widgets and device transforms, computing the size and shape of a pixel in local item coordinates, etc. Note that in item coordinates, a pixel does not have to be square or even rectangular, so just asking how to increase a bounding rect by 2px can be a rather complex task.
      """
      _pixelVectorGlobalCache = LRUCache(100, 70)
  
      def __init__(self, register=None):
          if not hasattr(self, '_qtBaseClass'):
              for b in self.__class__.__bases__:
                  if issubclass(b, QtGui.QGraphicsItem):
                      self.__class__._qtBaseClass = b
                      break
          if not hasattr(self, '_qtBaseClass'):
              raise Exception('Could not determine Qt base class for GraphicsItem: %s' % str(self))
  
          self._pixelVectorCache = [None, None]
          self._viewWidget = None
          self._viewBox = None
          self._connectedView = None
          self._exportOpts = False   ## If False, not currently exporting. Otherwise, contains dict of export options.
          self._cachedView = None
          if register is not None and register:
              warnings.warn(
                  "'register' argument is deprecated and does nothing, will be removed in 0.13",
                  DeprecationWarning, stacklevel=2
              )
  
      def getViewWidget(self):
          """
          Return the view widget for this item. 
          
          If the scene has multiple views, only the first view is returned.
          The return value is cached; clear the cached value with forgetViewWidget().
          If the view has been deleted by Qt, return None.
          """
          if self._viewWidget is None:
              scene = self.scene()
              if scene is None:
                  return None
              views = scene.views()
              if len(views) < 1:
                  return None
              self._viewWidget = weakref.ref(self.scene().views()[0])
              
          v = self._viewWidget()
          if v is not None and not isQObjectAlive(v):
              return None
              
          return v
      
      def forgetViewWidget(self):
          self._viewWidget = None
      
      def getViewBox(self):
          """
          Return the first ViewBox or GraphicsView which bounds this item's visible space.
          If this item is not contained within a ViewBox, then the GraphicsView is returned.
          If the item is contained inside nested ViewBoxes, then the inner-most ViewBox is returned.
          The result is cached; clear the cache with forgetViewBox()
          """
          if self._viewBox is None:
              p = self
              while True:
                  try:
                      p = p.parentItem()
                  except RuntimeError:  ## sometimes happens as items are being removed from a scene and collected.
                      return None
                  if p is None:
                      vb = self.getViewWidget()
                      if vb is None:
                          return None
                      else:
                          self._viewBox = weakref.ref(vb)
                          break
                  if hasattr(p, 'implements') and p.implements('ViewBox'):
                      self._viewBox = weakref.ref(p)
                      break
          return self._viewBox()  ## If we made it this far, _viewBox is definitely not None
  
      def forgetViewBox(self):
          self._viewBox = None
          
      def deviceTransform(self, viewportTransform=None):
          """
          Return the transform that converts local item coordinates to device coordinates (usually pixels).
          Extends deviceTransform to automatically determine the viewportTransform.
          """
          if viewportTransform is None:
              view = self.getViewWidget()
              if view is None:
                  return None
              viewportTransform = view.viewportTransform()
          dt = self._qtBaseClass.deviceTransform(self, viewportTransform)
          
          #xmag = abs(dt.m11())+abs(dt.m12())
          #ymag = abs(dt.m21())+abs(dt.m22())
          #if xmag * ymag == 0: 
          if dt.determinant() == 0:  ## occurs when deviceTransform is invalid because widget has not been displayed
              return None
          else:
              return dt
          
      def viewTransform(self):
          """Return the transform that maps from local coordinates to the item's ViewBox coordinates
          If there is no ViewBox, return the scene transform.
          Returns None if the item does not have a view."""
          view = self.getViewBox()
          if view is None:
              return None
          if hasattr(view, 'implements') and view.implements('ViewBox'):
              tr = self.itemTransform(view.innerSceneItem())
              if isinstance(tr, tuple):
                  tr = tr[0]   ## difference between pyside and pyqt
              return tr
          else:
              return self.sceneTransform()
              #return self.deviceTransform(view.viewportTransform())
  
  
  
      def getBoundingParents(self):
          """Return a list of parents to this item that have child clipping enabled."""
          p = self
          parents = []
          while True:
              p = p.parentItem()
              if p is None:
                  break
              if p.flags() & self.ItemClipsChildrenToShape:
                  parents.append(p)
          return parents
      
      def viewRect(self):
          """Return the visible bounds of this item's ViewBox or GraphicsWidget,
          in the local coordinate system of the item."""
          if self._cachedView is not None:
              return self._cachedView
  
          # Note that in cases of early returns here, the view cache stays empty (None).
          view = self.getViewBox()
          if view is None:
              return None
          bounds = self.mapRectFromView(view.viewRect())
          if bounds is None:
              return None
  
          bounds = bounds.normalized()
          
          self._cachedView = bounds
              
          ## nah.
          #for p in self.getBoundingParents():
              #bounds &= self.mapRectFromScene(p.sceneBoundingRect())
  
          return bounds
          
          
          
      def pixelVectors(self, direction=None):
          """Return vectors in local coordinates representing the width and height of a view pixel.
          If direction is specified, then return vectors parallel and orthogonal to it.
          
          Return (None, None) if pixel size is not yet defined (usually because the item has not yet been displayed)
          or if pixel size is below floating-point precision limit.
          """
          
          ## This is an expensive function that gets called very frequently.
          ## We have two levels of cache to try speeding things up.
          
          dt = self.deviceTransform()
          if dt is None:
              return None, None
              
          ## Ignore translation. If the translation is much larger than the scale
          ## (such as when looking at unix timestamps), we can get floating-point errors.
          dt.setMatrix(dt.m11(), dt.m12(), 0, dt.m21(), dt.m22(), 0, 0, 0, 1)
          
          if direction is None:
              direction = QtCore.QPointF(1, 0)
          elif direction.manhattanLength() == 0:
              raise Exception("Cannot compute pixel length for 0-length vector.")
  
          key = (dt.m11(), dt.m21(), dt.m12(), dt.m22(), direction.x(), direction.y())
  
          ## check local cache
          if key == self._pixelVectorCache[0]:
              return tuple(map(Point, self._pixelVectorCache[1]))  ## return a *copy*
  
          ## check global cache
          pv = self._pixelVectorGlobalCache.get(key, None)
          if pv is not None:
              self._pixelVectorCache = [key, pv]
              return tuple(map(Point,pv))  ## return a *copy*
          
          ## attempt to re-scale direction vector to fit within the precision of the coordinate system
          ## Here's the problem: we need to map the vector 'direction' from the item to the device, via transform 'dt'.
          ## In some extreme cases, this mapping can fail unless the length of 'direction' is cleverly chosen.
          ## Example:
          ##   dt = [ 1, 0,    2 
          ##          0, 2, 1e20
          ##          0, 0,    1 ]
          ## Then we map the origin (0,0) and direction (0,1) and get:
          ##    o' = 2,1e20
          ##    d' = 2,1e20  <-- should be 1e20+2, but this can't be represented with a 32-bit float
          ##    
          ##    |o' - d'|  == 0    <-- this is the problem.
          
          ## Perhaps the easiest solution is to exclude the transformation column from dt. Does this cause any other problems?
          
          #if direction.x() == 0:
              #r = abs(dt.m32())/(abs(dt.m12()) + abs(dt.m22()))
              ##r = 1.0/(abs(dt.m12()) + abs(dt.m22()))
          #elif direction.y() == 0:
              #r = abs(dt.m31())/(abs(dt.m11()) + abs(dt.m21()))
              ##r = 1.0/(abs(dt.m11()) + abs(dt.m21()))
          #else:
              #r = ((abs(dt.m32())/(abs(dt.m12()) + abs(dt.m22()))) * (abs(dt.m31())/(abs(dt.m11()) + abs(dt.m21()))))**0.5
          #if r == 0:
              #r = 1.  ## shouldn't need to do this; probably means the math above is wrong?
          #directionr = direction * r
          directionr = direction
          
          ## map direction vector onto device
          #viewDir = Point(dt.map(directionr) - dt.map(Point(0,0)))
          #mdirection = dt.map(directionr)
          dirLine = QtCore.QLineF(QtCore.QPointF(0,0), directionr)
          viewDir = dt.map(dirLine)
          if viewDir.length() == 0:
              return None, None   ##  pixel size cannot be represented on this scale
             
          ## get unit vector and orthogonal vector (length of pixel)
          #orthoDir = Point(viewDir[1], -viewDir[0])  ## orthogonal to line in pixel-space
          try:  
              normView = viewDir.unitVector()
              #normView = viewDir.norm()  ## direction of one pixel orthogonal to line
              normOrtho = normView.normalVector()
              #normOrtho = orthoDir.norm()
          except:
              raise Exception("Invalid direction %s" %directionr)
              
          ## map back to item 
          dti = fn.invertQTransform(dt)
          #pv = Point(dti.map(normView)-dti.map(Point(0,0))), Point(dti.map(normOrtho)-dti.map(Point(0,0)))
          pv = Point(dti.map(normView).p2()), Point(dti.map(normOrtho).p2())
          self._pixelVectorCache[1] = pv
          self._pixelVectorCache[0] = dt
          self._pixelVectorGlobalCache[key] = pv
          return self._pixelVectorCache[1]
      
          
      def pixelLength(self, direction, ortho=False):
          """Return the length of one pixel in the direction indicated (in local coordinates)
          If ortho=True, then return the length of one pixel orthogonal to the direction indicated.
          
          Return None if pixel size is not yet defined (usually because the item has not yet been displayed).
          """
          normV, orthoV = self.pixelVectors(direction)
          if normV == None or orthoV == None:
              return None
          if ortho:
              return orthoV.length()
          return normV.length()
          
  
      def pixelSize(self):
          ## deprecated
          v = self.pixelVectors()
          if v == (None, None):
              return None, None
          return (v[0].x()**2+v[0].y()**2)**0.5, (v[1].x()**2+v[1].y()**2)**0.5
  
      def pixelWidth(self):
          ## deprecated
          vt = self.deviceTransform()
          if vt is None:
              return 0
          vt = fn.invertQTransform(vt)
          return vt.map(QtCore.QLineF(0, 0, 1, 0)).length()
          
      def pixelHeight(self):
          ## deprecated
          vt = self.deviceTransform()
          if vt is None:
              return 0
          vt = fn.invertQTransform(vt)
          return vt.map(QtCore.QLineF(0, 0, 0, 1)).length()
          #return Point(vt.map(QtCore.QPointF(0, 1))-vt.map(QtCore.QPointF(0, 0))).length()
          
          
      def mapToDevice(self, obj):
          """
          Return *obj* mapped from local coordinates to device coordinates (pixels).
          If there is no device mapping available, return None.
          """
          vt = self.deviceTransform()
          if vt is None:
              return None
          return vt.map(obj)
          
      def mapFromDevice(self, obj):
          """
          Return *obj* mapped from device coordinates (pixels) to local coordinates.
          If there is no device mapping available, return None.
          """
          vt = self.deviceTransform()
          if vt is None:
              return None
          if isinstance(obj, QtCore.QPoint):
              obj = QtCore.QPointF(obj)
          vt = fn.invertQTransform(vt)
          return vt.map(obj)
  
      def mapRectToDevice(self, rect):
          """
          Return *rect* mapped from local coordinates to device coordinates (pixels).
          If there is no device mapping available, return None.
          """
          vt = self.deviceTransform()
          if vt is None:
              return None
          return vt.mapRect(rect)
  
      def mapRectFromDevice(self, rect):
          """
          Return *rect* mapped from device coordinates (pixels) to local coordinates.
          If there is no device mapping available, return None.
          """
          vt = self.deviceTransform()
          if vt is None:
              return None
          vt = fn.invertQTransform(vt)
          return vt.mapRect(rect)
      
      def mapToView(self, obj):
          vt = self.viewTransform()
          if vt is None:
              return None
          return vt.map(obj)
          
      def mapRectToView(self, obj):
          vt = self.viewTransform()
          if vt is None:
              return None
          return vt.mapRect(obj)
          
      def mapFromView(self, obj):
          vt = self.viewTransform()
          if vt is None:
              return None
          vt = fn.invertQTransform(vt)
          return vt.map(obj)
  
      def mapRectFromView(self, obj):
          vt = self.viewTransform()
          if vt is None:
              return None
          vt = fn.invertQTransform(vt)
          return vt.mapRect(obj)
  
      def pos(self):
          return Point(self._qtBaseClass.pos(self))
      
      def viewPos(self):
          return self.mapToView(self.mapFromParent(self.pos()))
      
      def parentItem(self):
          ## PyQt bug -- some items are returned incorrectly.
          return GraphicsScene.translateGraphicsItem(self._qtBaseClass.parentItem(self))
          
      def setParentItem(self, parent):
          ## Workaround for Qt bug: https://bugreports.qt-project.org/browse/QTBUG-18616
          if parent is not None:
              pscene = parent.scene()
              if pscene is not None and self.scene() is not pscene:
                  pscene.addItem(self)
          return self._qtBaseClass.setParentItem(self, parent)
      
      def childItems(self):
          ## PyQt bug -- some child items are returned incorrectly.
          return list(map(GraphicsScene.translateGraphicsItem, self._qtBaseClass.childItems(self)))
  
  
      def sceneTransform(self):
          ## Qt bug: do no allow access to sceneTransform() until 
          ## the item has a scene.
          
          if self.scene() is None:
              return self.transform()
          else:
              return self._qtBaseClass.sceneTransform(self)
  
  
      def transformAngle(self, relativeItem=None):
          """Return the rotation produced by this item's transform (this assumes there is no shear in the transform)
          If relativeItem is given, then the angle is determined relative to that item.
          """
          if relativeItem is None:
              relativeItem = self.parentItem()
              
  
          tr = self.itemTransform(relativeItem)
          if isinstance(tr, tuple):  ## difference between pyside and pyqt
              tr = tr[0]
          #vec = tr.map(Point(1,0)) - tr.map(Point(0,0))
          vec = tr.map(QtCore.QLineF(0,0,1,0))
          #return Point(vec).angle(Point(1,0))
          return vec.angleTo(QtCore.QLineF(vec.p1(), vec.p1()+QtCore.QPointF(1,0)))
          
      #def itemChange(self, change, value):
          #ret = self._qtBaseClass.itemChange(self, change, value)
          #if change == self.ItemParentHasChanged or change == self.ItemSceneHasChanged:
              #print "Item scene changed:", self
              #self.setChildScene(self)  ## This is bizarre.
          #return ret
  
      #def setChildScene(self, ch):
          #scene = self.scene()
          #for ch2 in ch.childItems():
              #if ch2.scene() is not scene:
                  #print "item", ch2, "has different scene:", ch2.scene(), scene
                  #scene.addItem(ch2)
                  #QtGui.QApplication.processEvents()
                  #print "   --> ", ch2.scene()
              #self.setChildScene(ch2)
  
      def parentChanged(self):
          """Called when the item's parent has changed. 
          This method handles connecting / disconnecting from ViewBox signals
          to make sure viewRangeChanged works properly. It should generally be 
          extended, not overridden."""
          self._updateView()
          
  
      def _updateView(self):
          ## called to see whether this item has a new view to connect to
          ## NOTE: This is called from GraphicsObject.itemChange or GraphicsWidget.itemChange.
  
          if not hasattr(self, '_connectedView'):
              # Happens when Python is shutting down.
              return
  
          ## It is possible this item has moved to a different ViewBox or widget;
          ## clear out previously determined references to these.
          self.forgetViewBox()
          self.forgetViewWidget()
          
          ## check for this item's current viewbox or view widget
          view = self.getViewBox()
          #if view is None:
              ##print "  no view"
              #return
  
          oldView = None
          if self._connectedView is not None:
              oldView = self._connectedView()
              
          if view is oldView:
              #print "  already have view", view
              return
  
          ## disconnect from previous view
          if oldView is not None:
              for signal, slot in [('sigRangeChanged', self.viewRangeChanged),
                                   ('sigDeviceRangeChanged', self.viewRangeChanged), 
                                   ('sigTransformChanged', self.viewTransformChanged), 
                                   ('sigDeviceTransformChanged', self.viewTransformChanged)]:
                  try:
                      getattr(oldView, signal).disconnect(slot)
                  except (TypeError, AttributeError, RuntimeError):
                      # TypeError and RuntimeError are from pyqt and pyside, respectively
                      pass
              
              self._connectedView = None
  
          ## connect to new view
          if view is not None:
              #print "connect:", self, view
              if hasattr(view, 'sigDeviceRangeChanged'):
                  # connect signals from GraphicsView
                  view.sigDeviceRangeChanged.connect(self.viewRangeChanged)
                  view.sigDeviceTransformChanged.connect(self.viewTransformChanged)
              else:
                  # connect signals from ViewBox
                  view.sigRangeChanged.connect(self.viewRangeChanged)
                  view.sigTransformChanged.connect(self.viewTransformChanged)
              self._connectedView = weakref.ref(view)
              self.viewRangeChanged()
              self.viewTransformChanged()
          
          ## inform children that their view might have changed
          self._replaceView(oldView)
          
          self.viewChanged(view, oldView)
          
      def viewChanged(self, view, oldView):
          """Called when this item's view has changed
          (ie, the item has been added to or removed from a ViewBox)"""
          pass
          
      def _replaceView(self, oldView, item=None):
          if item is None:
              item = self
          for child in item.childItems():
              if isinstance(child, GraphicsItem):
                  if child.getViewBox() is oldView:
                      child._updateView()
                          #self._replaceView(oldView, child)
              else:
                  self._replaceView(oldView, child)
          
          
  
      def viewRangeChanged(self):
          """
          Called whenever the view coordinates of the ViewBox containing this item have changed.
          """
          pass
      
      def viewTransformChanged(self):
          """
          Called whenever the transformation matrix of the view has changed.
          (eg, the view range has changed or the view was resized)
          Invalidates the viewRect cache.
          """
          self._cachedView = None
      
      #def prepareGeometryChange(self):
          #self._qtBaseClass.prepareGeometryChange(self)
          #self.informViewBoundsChanged()
          
      def informViewBoundsChanged(self):
          """
          Inform this item's container ViewBox that the bounds of this item have changed.
          This is used by ViewBox to react if auto-range is enabled.
          """
          view = self.getViewBox()
          if view is not None and hasattr(view, 'implements') and view.implements('ViewBox'):
              view.itemBoundsChanged(self)  ## inform view so it can update its range if it wants
      
      def childrenShape(self):
          """Return the union of the shapes of all descendants of this item in local coordinates."""
          childs = self.allChildItems()
          shapes = [self.mapFromItem(c, c.shape()) for c in self.allChildItems()]
          return reduce(operator.add, shapes)
      
      def allChildItems(self, root=None):
          """Return list of the entire item tree descending from this item."""
          if root is None:
              root = self
          tree = []
          for ch in root.childItems():
              tree.append(ch)
              tree.extend(self.allChildItems(ch))
          return tree
      
      
      def setExportMode(self, export, opts=None):
          """
          This method is called by exporters to inform items that they are being drawn for export
          with a specific set of options. Items access these via self._exportOptions.
          When exporting is complete, _exportOptions is set to False.
          """
          if opts is None:
              opts = {}
          if export:
              self._exportOpts = opts
              #if 'antialias' not in opts:
                  #self._exportOpts['antialias'] = True
          else:
              self._exportOpts = False
      
      #def update(self):
          #self._qtBaseClass.update(self)
          #print "Update:", self
  
      def getContextMenus(self, event):
          return [self.getMenu()] if hasattr(self, "getMenu") else []
  