Skip to main content
`Ctrl`+`K`

# Source code for pyqtgraph.graphicsItems.GraphicsItem

    __all__ = ['GraphicsItem']

    import operator
    import weakref
    from collections import OrderedDict
    from functools import reduce
    from math import hypot
    from typing import Optional
    from xml.etree.ElementTree import Element

    from .. import functions as fn
    from ..GraphicsScene import GraphicsScene
    from ..Point import Point
    from ..Qt import QtCore, QtWidgets, isQObjectAlive

    # Recipe from https://docs.python.org/3.8/library/collections.html#collections.OrderedDict
    # slightly adapted for Python 3.7 compatibility
    class LRU(OrderedDict):
        'Limit size, evicting the least recently looked-up key when full'

        def __init__(self, maxsize=128, *args, **kwds):
            self.maxsize = maxsize
            super().__init__(*args, **kwds)

        def __getitem__(self, key):
            value = super().__getitem__(key)
            self.move_to_end(key)
            return value

        def __setitem__(self, key, value):
            if key in self:
                self.move_to_end(key)
            super().__setitem__(key, value)
            if len(self) > self.maxsize:
                oldest = next(iter(self))
                del self[oldest]

    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 = LRU(100)

        def __init__(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

        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):
            """
            Return the transform that converts local item coordinates to device coordinates (usually pixels).
            """
            if (view := self.getViewWidget()) is None:
                return None
            viewportTransform = view.viewportTransform()
            dt = self.deviceTransform(viewportTransform)

            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'):
                return self.itemTransform(view.innerSceneItem())[0]
            else:
                return self.sceneTransform()

        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.GraphicsItemFlag.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.

            if (dt := self.deviceTransform_()) 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] = key
            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 is None or orthoV is 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 (hypot(v[0].x(), v[0].y()), hypot(v[1].x(), v[1].y()))  # lengths

        def pixelWidth(self):
            ## deprecated
            if (vt := self.deviceTransform_()) is None:
                return 0
            vt = fn.invertQTransform(vt)
            return vt.map(QtCore.QLineF(0, 0, 1, 0)).length()

        def pixelHeight(self):
            ## deprecated
            if (vt := self.deviceTransform_()) 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.
            """
            if (vt := self.deviceTransform_()) 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.
            """
            if (vt := self.deviceTransform_()) 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.
            """
            if (vt := self.deviceTransform_()) 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.
            """
            if (vt := self.deviceTransform_()) 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 viewPos(self):
            return self.mapToView(self.mapFromParent(self.pos()))

        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)[0]
            vec = tr.map(QtCore.QLineF(0,0,1,0))
            return vec.angleTo(QtCore.QLineF(vec.p1(), vec.p1()+QtCore.QPointF(1,0)))

        def changeParent(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:
                Device = 'Device' if hasattr(oldView, 'sigDeviceRangeChanged') else ''
                for signal, slot in [(f'sig{Device}RangeChanged', self.viewRangeChanged),
                                     (f'sig{Device}TransformChanged', 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)"""

        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)

        @QtCore.Slot()
        def viewRangeChanged(self):
            """
            Called whenever the view coordinates of the ViewBox containing this item have changed.
            """

            # when this is called, _cachedView is not invalidated.
            # this means that for functions overriding viewRangeChanged, viewRect() may be stale.

        @QtCore.Slot()
        def viewTransformChanged(self):
            """
            Called whenever the transformation matrix of the view has changed.
            For example, when the view range has changed or the view was resized.
            Invalidates the viewRect cache.
            """
            self._cachedView = None

        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."""
            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 getContextMenus(self, event):
            return [self.getMenu()] if hasattr(self, "getMenu") else []

        def generateSvg(
                self,
                nodes: dict[str, Element]
        ) -> Optional[tuple[Element, list[Element]]]:
            """Method to override to manually specify the SVG writer mechanism.

            Parameters
            ----------
            nodes
                Dictionary keyed by the name of graphics items and the XML
                representation of the the item that can be written as valid
                SVG.

            Returns
            -------
            tuple
                First element is the top level group for this item. The
                second element is a list of xml Elements corresponding to the
                child nodes of the item.
            None
                Return None if no XML is needed for rendering

            Raises
            ------
            NotImplementedError
                override method to implement in subclasses of GraphicsItem

            See Also
            --------
            pyqtgraph.exporters.SVGExporter._generateItemSvg
                The generic and default implementation

            """
            raise NotImplementedError