# Source code for pyqtgraph.graphicsItems.AxisItem

    from ..Qt import QtGui, QtCore
    from ..python2_3 import asUnicode
    import numpy as np
    from ..Point import Point
    from .. import debug as debug
    import weakref
    from .. import functions as fn
    from .. import getConfigOption
    from .GraphicsWidget import GraphicsWidget

    __all__ = ['AxisItem']
    class AxisItem(GraphicsWidget):
        """
        GraphicsItem showing a single plot axis with ticks, values, and label.
        Can be configured to fit on any side of a plot, and can automatically synchronize its displayed scale with ViewBox items.
        Ticks can be extended to draw a grid.
        If maxTickLength is negative, ticks point into the plot.
        """

        def __init__(self, orientation, pen=None, linkView=None, parent=None, maxTickLength=-5, showValues=True):
            """
            ==============  ===============================================================
            **Arguments:**
            orientation     one of 'left', 'right', 'top', or 'bottom'
            maxTickLength   (px) maximum length of ticks to draw. Negative values draw
                            into the plot, positive values draw outward.
            linkView        (ViewBox) causes the range of values displayed in the axis
                            to be linked to the visible range of a ViewBox.
            showValues      (bool) Whether to display values adjacent to ticks
            pen             (QPen) Pen used when drawing ticks.
            ==============  ===============================================================
            """

            GraphicsWidget.__init__(self, parent)
            self.label = QtGui.QGraphicsTextItem(self)
            self.picture = None
            self.orientation = orientation
            if orientation not in ['left', 'right', 'top', 'bottom']:
                raise Exception("Orientation argument must be one of 'left', 'right', 'top', or 'bottom'.")
            if orientation in ['left', 'right']:
                self.label.rotate(-90)

            self.style = {
                'tickTextOffset': [5, 2],  ## (horizontal, vertical) spacing between text and axis
                'tickTextWidth': 30,  ## space reserved for tick text
                'tickTextHeight': 18,
                'autoExpandTextSpace': True,  ## automatically expand text space if needed
                'tickFont': None,
                'stopAxisAtTick': (False, False),  ## whether axis is drawn to edge of box or to last tick
                'textFillLimits': [  ## how much of the axis to fill up with tick text, maximally.
                    (0, 0.8),    ## never fill more than 80% of the axis
                    (2, 0.6),    ## If we already have 2 ticks with text, fill no more than 60% of the axis
                    (4, 0.4),    ## If we already have 4 ticks with text, fill no more than 40% of the axis
                    (6, 0.2),    ## If we already have 6 ticks with text, fill no more than 20% of the axis
                    ],
                'showValues': showValues,
                'tickLength': maxTickLength,
                'maxTickLevel': 2,
                'maxTextLevel': 2,
            }

            self.textWidth = 30  ## Keeps track of maximum width / height of tick text
            self.textHeight = 18

            # If the user specifies a width / height, remember that setting
            # indefinitely.
            self.fixedWidth = None
            self.fixedHeight = None

            self.labelText = ''
            self.labelUnits = ''
            self.labelUnitPrefix=''
            self.labelStyle = {}
            self.logMode = False
            self.tickFont = None

            self._tickLevels = None  ## used to override the automatic ticking system with explicit ticks
            self._tickSpacing = None  # used to override default tickSpacing method
            self.scale = 1.0
            self.autoSIPrefix = True
            self.autoSIPrefixScale = 1.0

            self.setRange(0, 1)

            if pen is None:
                self.setPen()
            else:
                self.setPen(pen)

            self._linkedView = None
            if linkView is not None:
                self.linkToView(linkView)

            self.showLabel(False)

            self.grid = False
            #self.setCacheMode(self.DeviceCoordinateCache)

        def setStyle(self, **kwds):
            """
            Set various style options.

            =================== =======================================================
            Keyword Arguments:
            tickLength          (int) The maximum length of ticks in pixels.
                                Positive values point toward the text; negative
                                values point away.
            tickTextOffset      (int) reserved spacing between text and axis in px
            tickTextWidth       (int) Horizontal space reserved for tick text in px
            tickTextHeight      (int) Vertical space reserved for tick text in px
            autoExpandTextSpace (bool) Automatically expand text space if the tick
                                strings become too long.
            tickFont            (QFont or None) Determines the font used for tick
                                values. Use None for the default font.
            stopAxisAtTick      (tuple: (bool min, bool max)) If True, the axis
                                line is drawn only as far as the last tick.
                                Otherwise, the line is drawn to the edge of the
                                AxisItem boundary.
            textFillLimits      (list of (tick #, % fill) tuples). This structure
                                determines how the AxisItem decides how many ticks
                                should have text appear next to them. Each tuple in
                                the list specifies what fraction of the axis length
                                may be occupied by text, given the number of ticks
                                that already have text displayed. For example::

                                    [(0, 0.8), # Never fill more than 80% of the axis
                                     (2, 0.6), # If we already have 2 ticks with text,
                                               # fill no more than 60% of the axis
                                     (4, 0.4), # If we already have 4 ticks with text,
                                               # fill no more than 40% of the axis
                                     (6, 0.2)] # If we already have 6 ticks with text,
                                               # fill no more than 20% of the axis

            showValues          (bool) indicates whether text is displayed adjacent
                                to ticks.
            =================== =======================================================

            Added in version 0.9.9
            """
            for kwd,value in kwds.items():
                if kwd not in self.style:
                    raise NameError("%s is not a valid style argument." % kwd)

                if kwd in ('tickLength', 'tickTextOffset', 'tickTextWidth', 'tickTextHeight'):
                    if not isinstance(value, int):
                        raise ValueError("Argument '%s' must be int" % kwd)

                if kwd == 'tickTextOffset':
                    if self.orientation in ('left', 'right'):
                        self.style['tickTextOffset'][0] = value
                    else:
                        self.style['tickTextOffset'][1] = value
                elif kwd == 'stopAxisAtTick':
                    try:
                        assert len(value) == 2 and isinstance(value[0], bool) and isinstance(value[1], bool)
                    except:
                        raise ValueError("Argument 'stopAxisAtTick' must have type (bool, bool)")
                    self.style[kwd] = value
                else:
                    self.style[kwd] = value

            self.picture = None
            self._adjustSize()
            self.update()

        def close(self):
            self.scene().removeItem(self.label)
            self.label = None
            self.scene().removeItem(self)

        def setGrid(self, grid):
            """Set the alpha value (0-255) for the grid, or False to disable.

            When grid lines are enabled, the axis tick lines are extended to cover
            the extent of the linked ViewBox, if any.
            """
            self.grid = grid
            self.picture = None
            self.prepareGeometryChange()
            self.update()

        def setLogMode(self, log):
            """
            If *log* is True, then ticks are displayed on a logarithmic scale and values
            are adjusted accordingly. (This is usually accessed by changing the log mode
            of a :func:`PlotItem <pyqtgraph.PlotItem.setLogMode>`)
            """
            self.logMode = log
            self.picture = None
            self.update()

        def setTickFont(self, font):
            self.tickFont = font
            self.picture = None
            self.prepareGeometryChange()
            ## Need to re-allocate space depending on font size?

            self.update()

        def resizeEvent(self, ev=None):
            #s = self.size()

            ## Set the position of the label
            nudge = 5
            br = self.label.boundingRect()
            p = QtCore.QPointF(0, 0)
            if self.orientation == 'left':
                p.setY(int(self.size().height()/2 + br.width()/2))
                p.setX(-nudge)
            elif self.orientation == 'right':
                p.setY(int(self.size().height()/2 + br.width()/2))
                p.setX(int(self.size().width()-br.height()+nudge))
            elif self.orientation == 'top':
                p.setY(-nudge)
                p.setX(int(self.size().width()/2. - br.width()/2.))
            elif self.orientation == 'bottom':
                p.setX(int(self.size().width()/2. - br.width()/2.))
                p.setY(int(self.size().height()-br.height()+nudge))
            self.label.setPos(p)
            self.picture = None

        def showLabel(self, show=True):
            """Show/hide the label text for this axis."""
            #self.drawLabel = show
            self.label.setVisible(show)
            if self.orientation in ['left', 'right']:
                self._updateWidth()
            else:
                self._updateHeight()
            if self.autoSIPrefix:
                self.updateAutoSIPrefix()

        def setLabel(self, text=None, units=None, unitPrefix=None, **args):
            """Set the text displayed adjacent to the axis.

            ==============  =============================================================
            **Arguments:**
            text            The text (excluding units) to display on the label for this
                            axis.
            units           The units for this axis. Units should generally be given
                            without any scaling prefix (eg, 'V' instead of 'mV'). The
                            scaling prefix will be automatically prepended based on the
                            range of data displayed.
            **args          All extra keyword arguments become CSS style options for
                            the <span> tag which will surround the axis label and units.
            ==============  =============================================================

            The final text generated for the label will look like::

                <span style="...options...">{text} (prefix{units})</span>

            Each extra keyword argument will become a CSS option in the above template.
            For example, you can set the font size and color of the label::

                labelStyle = {'color': '#FFF', 'font-size': '14pt'}
                axis.setLabel('label text', units='V', **labelStyle)

            """
            if text is not None:
                self.labelText = text
                self.showLabel()
            if units is not None:
                self.labelUnits = units
                self.showLabel()
            if unitPrefix is not None:
                self.labelUnitPrefix = unitPrefix
            if len(args) > 0:
                self.labelStyle = args
            self.label.setHtml(self.labelString())
            self._adjustSize()
            self.picture = None
            self.update()

        def labelString(self):
            if self.labelUnits == '':
                if not self.autoSIPrefix or self.autoSIPrefixScale == 1.0:
                    units = ''
                else:
                    units = asUnicode('(x%g)') % (1.0/self.autoSIPrefixScale)
            else:
                #print repr(self.labelUnitPrefix), repr(self.labelUnits)
                units = asUnicode('(%s%s)') % (asUnicode(self.labelUnitPrefix), asUnicode(self.labelUnits))

            s = asUnicode('%s %s') % (asUnicode(self.labelText), asUnicode(units))

            style = ';'.join(['%s: %s' % (k, self.labelStyle[k]) for k in self.labelStyle])

            return asUnicode("<span style='%s'>%s</span>") % (style, asUnicode(s))

        def _updateMaxTextSize(self, x):
            ## Informs that the maximum tick size orthogonal to the axis has
            ## changed; we use this to decide whether the item needs to be resized
            ## to accomodate.
            if self.orientation in ['left', 'right']:
                mx = max(self.textWidth, x)
                if mx > self.textWidth or mx < self.textWidth-10:
                    self.textWidth = mx
                    if self.style['autoExpandTextSpace'] is True:
                        self._updateWidth()
                        #return True  ## size has changed
            else:
                mx = max(self.textHeight, x)
                if mx > self.textHeight or mx < self.textHeight-10:
                    self.textHeight = mx
                    if self.style['autoExpandTextSpace'] is True:
                        self._updateHeight()
                        #return True  ## size has changed

        def _adjustSize(self):
            if self.orientation in ['left', 'right']:
                self._updateWidth()
            else:
                self._updateHeight()

        def setHeight(self, h=None):
            """Set the height of this axis reserved for ticks and tick labels.
            The height of the axis label is automatically added.

            If *height* is None, then the value will be determined automatically
            based on the size of the tick text."""
            self.fixedHeight = h
            self._updateHeight()

        def _updateHeight(self):
            if not self.isVisible():
                h = 0
            else:
                if self.fixedHeight is None:
                    if not self.style['showValues']:
                        h = 0
                    elif self.style['autoExpandTextSpace'] is True:
                        h = self.textHeight
                    else:
                        h = self.style['tickTextHeight']
                    h += self.style['tickTextOffset'][1] if self.style['showValues'] else 0
                    h += max(0, self.style['tickLength'])
                    if self.label.isVisible():
                        h += self.label.boundingRect().height() * 0.8
                else:
                    h = self.fixedHeight

            self.setMaximumHeight(h)
            self.setMinimumHeight(h)
            self.picture = None

        def setWidth(self, w=None):
            """Set the width of this axis reserved for ticks and tick labels.
            The width of the axis label is automatically added.

            If *width* is None, then the value will be determined automatically
            based on the size of the tick text."""
            self.fixedWidth = w
            self._updateWidth()

        def _updateWidth(self):
            if not self.isVisible():
                w = 0
            else:
                if self.fixedWidth is None:
                    if not self.style['showValues']:
                        w = 0
                    elif self.style['autoExpandTextSpace'] is True:
                        w = self.textWidth
                    else:
                        w = self.style['tickTextWidth']
                    w += self.style['tickTextOffset'][0] if self.style['showValues'] else 0
                    w += max(0, self.style['tickLength'])
                    if self.label.isVisible():
                        w += self.label.boundingRect().height() * 0.8  ## bounding rect is usually an overestimate
                else:
                    w = self.fixedWidth

            self.setMaximumWidth(w)
            self.setMinimumWidth(w)
            self.picture = None

        def pen(self):
            if self._pen is None:
                return fn.mkPen(getConfigOption('foreground'))
            return fn.mkPen(self._pen)

        def setPen(self, *args, **kwargs):
            """
            Set the pen used for drawing text, axes, ticks, and grid lines.
            If no arguments are given, the default foreground color will be used
            (see :func:`setConfigOption <pyqtgraph.setConfigOption>`).
            """
            self.picture = None
            if args or kwargs:
                self._pen = fn.mkPen(*args, **kwargs)
            else:
                self._pen = fn.mkPen(getConfigOption('foreground'))
            self.labelStyle['color'] = '#' + fn.colorStr(self._pen.color())[:6]
            self.setLabel()
            self.update()

        def setScale(self, scale=None):
            """
            Set the value scaling for this axis.

            Setting this value causes the axis to draw ticks and tick labels as if
            the view coordinate system were scaled. By default, the axis scaling is
            1.0.
            """
            # Deprecated usage, kept for backward compatibility
            if scale is None:
                scale = 1.0
                self.enableAutoSIPrefix(True)

            if scale != self.scale:
                self.scale = scale
                self.setLabel()
                self.picture = None
                self.update()

        def enableAutoSIPrefix(self, enable=True):
            """
            Enable (or disable) automatic SI prefix scaling on this axis.

            When enabled, this feature automatically determines the best SI prefix
            to prepend to the label units, while ensuring that axis values are scaled
            accordingly.

            For example, if the axis spans values from -0.1 to 0.1 and has units set
            to 'V' then the axis would display values -100 to 100
            and the units would appear as 'mV'

            This feature is enabled by default, and is only available when a suffix
            (unit string) is provided to display on the label.
            """
            self.autoSIPrefix = enable
            self.updateAutoSIPrefix()

        def updateAutoSIPrefix(self):
            if self.label.isVisible():
                (scale, prefix) = fn.siScale(max(abs(self.range[0]*self.scale), abs(self.range[1]*self.scale)))
                if self.labelUnits == '' and prefix in ['k', 'm']:  ## If we are not showing units, wait until 1e6 before scaling.
                    scale = 1.0
                    prefix = ''
                self.setLabel(unitPrefix=prefix)
            else:
                scale = 1.0

            self.autoSIPrefixScale = scale
            self.picture = None
            self.update()

        def setRange(self, mn, mx):
            """Set the range of values displayed by the axis.
            Usually this is handled automatically by linking the axis to a ViewBox with :func:`linkToView <pyqtgraph.AxisItem.linkToView>`"""
            if any(np.isinf((mn, mx))) or any(np.isnan((mn, mx))):
                raise Exception("Not setting range to [%s, %s]" % (str(mn), str(mx)))
            self.range = [mn, mx]
            if self.autoSIPrefix:
                self.updateAutoSIPrefix()
            self.picture = None
            self.update()

        def linkedView(self):
            """Return the ViewBox this axis is linked to"""
            if self._linkedView is None:
                return None
            else:
                return self._linkedView()

        def linkToView(self, view):
            """Link this axis to a ViewBox, causing its displayed range to match the visible range of the view."""
            oldView = self.linkedView()
            self._linkedView = weakref.ref(view)
            if self.orientation in ['right', 'left']:
                if oldView is not None:
                    oldView.sigYRangeChanged.disconnect(self.linkedViewChanged)
                view.sigYRangeChanged.connect(self.linkedViewChanged)
            else:
                if oldView is not None:
                    oldView.sigXRangeChanged.disconnect(self.linkedViewChanged)
                view.sigXRangeChanged.connect(self.linkedViewChanged)

            if oldView is not None:
                oldView.sigResized.disconnect(self.linkedViewChanged)
            view.sigResized.connect(self.linkedViewChanged)

        def linkedViewChanged(self, view, newRange=None):
            if self.orientation in ['right', 'left']:
                if newRange is None:
                    newRange = view.viewRange()[1]
                if view.yInverted():
                    self.setRange(*newRange[::-1])
                else:
                    self.setRange(*newRange)
            else:
                if newRange is None:
                    newRange = view.viewRange()[0]
                if view.xInverted():
                    self.setRange(*newRange[::-1])
                else:
                    self.setRange(*newRange)

        def boundingRect(self):
            linkedView = self.linkedView()
            if linkedView is None or self.grid is False:
                rect = self.mapRectFromParent(self.geometry())
                ## extend rect if ticks go in negative direction
                ## also extend to account for text that flows past the edges
                tl = self.style['tickLength']
                if self.orientation == 'left':
                    rect = rect.adjusted(0, -15, -min(0,tl), 15)
                elif self.orientation == 'right':
                    rect = rect.adjusted(min(0,tl), -15, 0, 15)
                elif self.orientation == 'top':
                    rect = rect.adjusted(-15, 0, 15, -min(0,tl))
                elif self.orientation == 'bottom':
                    rect = rect.adjusted(-15, min(0,tl), 15, 0)
                return rect
            else:
                return self.mapRectFromParent(self.geometry()) | linkedView.mapRectToItem(self, linkedView.boundingRect())

        def paint(self, p, opt, widget):
            profiler = debug.Profiler()
            if self.picture is None:
                try:
                    picture = QtGui.QPicture()
                    painter = QtGui.QPainter(picture)
                    specs = self.generateDrawSpecs(painter)
                    profiler('generate specs')
                    if specs is not None:
                        self.drawPicture(painter, *specs)
                        profiler('draw picture')
                finally:
                    painter.end()
                self.picture = picture
            #p.setRenderHint(p.Antialiasing, False)   ## Sometimes we get a segfault here ???
            #p.setRenderHint(p.TextAntialiasing, True)
            self.picture.play(p)

        def setTicks(self, ticks):
            """Explicitly determine which ticks to display.
            This overrides the behavior specified by tickSpacing(), tickValues(), and tickStrings()
            The format for *ticks* looks like::

                [
                    [ (majorTickValue1, majorTickString1), (majorTickValue2, majorTickString2), ... ],
                    [ (minorTickValue1, minorTickString1), (minorTickValue2, minorTickString2), ... ],
                    ...
                ]

            If *ticks* is None, then the default tick system will be used instead.
            """
            self._tickLevels = ticks
            self.picture = None
            self.update()

        def setTickSpacing(self, major=None, minor=None, levels=None):
            """
            Explicitly determine the spacing of major and minor ticks. This
            overrides the default behavior of the tickSpacing method, and disables
            the effect of setTicks(). Arguments may be either *major* and *minor*,
            or *levels* which is a list of (spacing, offset) tuples for each
            tick level desired.

            If no arguments are given, then the default behavior of tickSpacing
            is enabled.

            Examples::

                # two levels, all offsets = 0
                axis.setTickSpacing(5, 1)
                # three levels, all offsets = 0
                axis.setTickSpacing([(3, 0), (1, 0), (0.25, 0)])
                # reset to default
                axis.setTickSpacing()
            """

            if levels is None:
                if major is None:
                    levels = None
                else:
                    levels = [(major, 0), (minor, 0)]
            self._tickSpacing = levels
            self.picture = None
            self.update()

        def tickSpacing(self, minVal, maxVal, size):
            """Return values describing the desired spacing and offset of ticks.

            This method is called whenever the axis needs to be redrawn and is a
            good method to override in subclasses that require control over tick locations.

            The return value must be a list of tuples, one for each set of ticks::

                [
                    (major tick spacing, offset),
                    (minor tick spacing, offset),
                    (sub-minor tick spacing, offset),
                    ...
                ]
            """
            # First check for override tick spacing
            if self._tickSpacing is not None:
                return self._tickSpacing

            dif = abs(maxVal - minVal)
            if dif == 0:
                return []

            ## decide optimal minor tick spacing in pixels (this is just aesthetics)
            optimalTickCount = max(2., np.log(size))

            ## optimal minor tick spacing
            optimalSpacing = dif / optimalTickCount

            ## the largest power-of-10 spacing which is smaller than optimal
            p10unit = 10 ** np.floor(np.log10(optimalSpacing))

            ## Determine major/minor tick spacings which flank the optimal spacing.
            intervals = np.array([1., 2., 10., 20., 100.]) * p10unit
            minorIndex = 0
            while intervals[minorIndex+1] <= optimalSpacing:
                minorIndex += 1

            levels = [
                (intervals[minorIndex+2], 0),
                (intervals[minorIndex+1], 0),
                #(intervals[minorIndex], 0)    ## Pretty, but eats up CPU
            ]

            if self.style['maxTickLevel'] >= 2:
                ## decide whether to include the last level of ticks
                minSpacing = min(size / 20., 30.)
                maxTickCount = size / minSpacing
                if dif / intervals[minorIndex] <= maxTickCount:
                    levels.append((intervals[minorIndex], 0))
                return levels

            ##### This does not work -- switching between 2/5 confuses the automatic text-level-selection
            ### Determine major/minor tick spacings which flank the optimal spacing.
            #intervals = np.array([1., 2., 5., 10., 20., 50., 100.]) * p10unit
            #minorIndex = 0
            #while intervals[minorIndex+1] <= optimalSpacing:
                #minorIndex += 1

            ### make sure we never see 5 and 2 at the same time
            #intIndexes = [
                #[0,1,3],
                #[0,2,3],
                #[2,3,4],
                #[3,4,6],
                #[3,5,6],
            #][minorIndex]

            #return [
                #(intervals[intIndexes[2]], 0),
                #(intervals[intIndexes[1]], 0),
                #(intervals[intIndexes[0]], 0)
            #]

        def tickValues(self, minVal, maxVal, size):
            """
            Return the values and spacing of ticks to draw::

                [
                    (spacing, [major ticks]),
                    (spacing, [minor ticks]),
                    ...
                ]

            By default, this method calls tickSpacing to determine the correct tick locations.
            This is a good method to override in subclasses.
            """
            minVal, maxVal = sorted((minVal, maxVal))

            minVal *= self.scale
            maxVal *= self.scale
            #size *= self.scale

            ticks = []
            tickLevels = self.tickSpacing(minVal, maxVal, size)
            allValues = np.array([])
            for i in range(len(tickLevels)):
                spacing, offset = tickLevels[i]

                ## determine starting tick
                start = (np.ceil((minVal-offset) / spacing) * spacing) + offset

                ## determine number of ticks
                num = int((maxVal-start) / spacing) + 1
                values = (np.arange(num) * spacing + start) / self.scale
                ## remove any ticks that were present in higher levels
                ## we assume here that if the difference between a tick value and a previously seen tick value
                ## is less than spacing/100, then they are 'equal' and we can ignore the new tick.
                values = list(filter(lambda x: all(np.abs(allValues-x) > spacing*0.01), values) )
                allValues = np.concatenate([allValues, values])
                ticks.append((spacing/self.scale, values))

            if self.logMode:
                return self.logTickValues(minVal, maxVal, size, ticks)

            #nticks = []
            #for t in ticks:
                #nvals = []
                #for v in t[1]:
                    #nvals.append(v/self.scale)
                #nticks.append((t[0]/self.scale,nvals))
            #ticks = nticks

            return ticks

        def logTickValues(self, minVal, maxVal, size, stdTicks):

            ## start with the tick spacing given by tickValues().
            ## Any level whose spacing is < 1 needs to be converted to log scale

            ticks = []
            for (spacing, t) in stdTicks:
                if spacing >= 1.0:
                    ticks.append((spacing, t))

            if len(ticks) < 3:
                v1 = int(np.floor(minVal))
                v2 = int(np.ceil(maxVal))
                #major = list(range(v1+1, v2))

                minor = []
                for v in range(v1, v2):
                    minor.extend(v + np.log10(np.arange(1, 10)))
                minor = [x for x in minor if x>minVal and x<maxVal]
                ticks.append((None, minor))
            return ticks

        def tickStrings(self, values, scale, spacing):
            """Return the strings that should be placed next to ticks. This method is called
            when redrawing the axis and is a good method to override in subclasses.
            The method is called with a list of tick values, a scaling factor (see below), and the
            spacing between ticks (this is required since, in some instances, there may be only
            one tick and thus no other way to determine the tick spacing)

            The scale argument is used when the axis label is displaying units which may have an SI scaling prefix.
            When determining the text to display, use value*scale to correctly account for this prefix.
            For example, if the axis label's units are set to 'V', then a tick value of 0.001 might
            be accompanied by a scale value of 1000. This indicates that the label is displaying 'mV', and
            thus the tick should display 0.001 * 1000 = 1.
            """
            if self.logMode:
                return self.logTickStrings(values, scale, spacing)

            places = max(0, np.ceil(-np.log10(spacing*scale)))
            strings = []
            for v in values:
                vs = v * scale
                if abs(vs) < .001 or abs(vs) >= 10000:
                    vstr = "%g" % vs
                else:
                    vstr = ("%%0.%df" % places) % vs
                strings.append(vstr)
            return strings

        def logTickStrings(self, values, scale, spacing):
            return ["%0.1g"%x for x in 10 ** np.array(values).astype(float)]

        def generateDrawSpecs(self, p):
            """
            Calls tickValues() and tickStrings() to determine where and how ticks should
            be drawn, then generates from this a set of drawing commands to be
            interpreted by drawPicture().
            """
            profiler = debug.Profiler()

            #bounds = self.boundingRect()
            bounds = self.mapRectFromParent(self.geometry())

            linkedView = self.linkedView()
            if linkedView is None or self.grid is False:
                tickBounds = bounds
            else:
                tickBounds = linkedView.mapRectToItem(self, linkedView.boundingRect())

            if self.orientation == 'left':
                span = (bounds.topRight(), bounds.bottomRight())
                tickStart = tickBounds.right()
                tickStop = bounds.right()
                tickDir = -1
                axis = 0
            elif self.orientation == 'right':
                span = (bounds.topLeft(), bounds.bottomLeft())
                tickStart = tickBounds.left()
                tickStop = bounds.left()
                tickDir = 1
                axis = 0
            elif self.orientation == 'top':
                span = (bounds.bottomLeft(), bounds.bottomRight())
                tickStart = tickBounds.bottom()
                tickStop = bounds.bottom()
                tickDir = -1
                axis = 1
            elif self.orientation == 'bottom':
                span = (bounds.topLeft(), bounds.topRight())
                tickStart = tickBounds.top()
                tickStop = bounds.top()
                tickDir = 1
                axis = 1
            #print tickStart, tickStop, span

            ## determine size of this item in pixels
            points = list(map(self.mapToDevice, span))
            if None in points:
                return
            lengthInPixels = Point(points[1] - points[0]).length()
            if lengthInPixels == 0:
                return

            # Determine major / minor / subminor axis ticks
            if self._tickLevels is None:
                tickLevels = self.tickValues(self.range[0], self.range[1], lengthInPixels)
                tickStrings = None
            else:
                ## parse self.tickLevels into the formats returned by tickLevels() and tickStrings()
                tickLevels = []
                tickStrings = []
                for level in self._tickLevels:
                    values = []
                    strings = []
                    tickLevels.append((None, values))
                    tickStrings.append(strings)
                    for val, strn in level:
                        values.append(val)
                        strings.append(strn)

            ## determine mapping between tick values and local coordinates
            dif = self.range[1] - self.range[0]
            if dif == 0:
                xScale = 1
                offset = 0
            else:
                if axis == 0:
                    xScale = -bounds.height() / dif
                    offset = self.range[0] * xScale - bounds.height()
                else:
                    xScale = bounds.width() / dif
                    offset = self.range[0] * xScale

            xRange = [x * xScale - offset for x in self.range]
            xMin = min(xRange)
            xMax = max(xRange)

            profiler('init')

            tickPositions = [] # remembers positions of previously drawn ticks

            ## compute coordinates to draw ticks
            ## draw three different intervals, long ticks first
            tickSpecs = []
            for i in range(len(tickLevels)):
                tickPositions.append([])
                ticks = tickLevels[i][1]

                ## length of tick
                tickLength = self.style['tickLength'] / ((i*0.5)+1.0)

                lineAlpha = 255 / (i+1)
                if self.grid is not False:
                    lineAlpha *= self.grid/255. * np.clip((0.05  * lengthInPixels / (len(ticks)+1)), 0., 1.)

                for v in ticks:
                    ## determine actual position to draw this tick
                    x = (v * xScale) - offset
                    if x < xMin or x > xMax:  ## last check to make sure no out-of-bounds ticks are drawn
                        tickPositions[i].append(None)
                        continue
                    tickPositions[i].append(x)

                    p1 = [x, x]
                    p2 = [x, x]
                    p1[axis] = tickStart
                    p2[axis] = tickStop
                    if self.grid is False:
                        p2[axis] += tickLength*tickDir
                    tickPen = self.pen()
                    color = tickPen.color()
                    color.setAlpha(lineAlpha)
                    tickPen.setColor(color)
                    tickSpecs.append((tickPen, Point(p1), Point(p2)))
            profiler('compute ticks')

            if self.style['stopAxisAtTick'][0] is True:
                stop = max(span[0].y(), min(map(min, tickPositions)))
                if axis == 0:
                    span[0].setY(stop)
                else:
                    span[0].setX(stop)
            if self.style['stopAxisAtTick'][1] is True:
                stop = min(span[1].y(), max(map(max, tickPositions)))
                if axis == 0:
                    span[1].setY(stop)
                else:
                    span[1].setX(stop)
            axisSpec = (self.pen(), span[0], span[1])

            textOffset = self.style['tickTextOffset'][axis]  ## spacing between axis and text
            #if self.style['autoExpandTextSpace'] is True:
                #textWidth = self.textWidth
                #textHeight = self.textHeight
            #else:
                #textWidth = self.style['tickTextWidth'] ## space allocated for horizontal text
                #textHeight = self.style['tickTextHeight'] ## space allocated for horizontal text

            textSize2 = 0
            textRects = []
            textSpecs = []  ## list of draw

            # If values are hidden, return early
            if not self.style['showValues']:
                return (axisSpec, tickSpecs, textSpecs)

            for i in range(min(len(tickLevels), self.style['maxTextLevel']+1)):
                ## Get the list of strings to display for this level
                if tickStrings is None:
                    spacing, values = tickLevels[i]
                    strings = self.tickStrings(values, self.autoSIPrefixScale * self.scale, spacing)
                else:
                    strings = tickStrings[i]

                if len(strings) == 0:
                    continue

                ## ignore strings belonging to ticks that were previously ignored
                for j in range(len(strings)):
                    if tickPositions[i][j] is None:
                        strings[j] = None

                ## Measure density of text; decide whether to draw this level
                rects = []
                for s in strings:
                    if s is None:
                        rects.append(None)
                    else:
                        br = p.boundingRect(QtCore.QRectF(0, 0, 100, 100), QtCore.Qt.AlignCenter, asUnicode(s))
                        ## boundingRect is usually just a bit too large
                        ## (but this probably depends on per-font metrics?)
                        br.setHeight(br.height() * 0.8)

                        rects.append(br)
                        textRects.append(rects[-1])

                if len(textRects) > 0:
                    ## measure all text, make sure there's enough room
                    if axis == 0:
                        textSize = np.sum([r.height() for r in textRects])
                        textSize2 = np.max([r.width() for r in textRects])
                    else:
                        textSize = np.sum([r.width() for r in textRects])
                        textSize2 = np.max([r.height() for r in textRects])
                else:
                    textSize = 0
                    textSize2 = 0

                if i > 0:  ## always draw top level
                    ## If the strings are too crowded, stop drawing text now.
                    ## We use three different crowding limits based on the number
                    ## of texts drawn so far.
                    textFillRatio = float(textSize) / lengthInPixels
                    finished = False
                    for nTexts, limit in self.style['textFillLimits']:
                        if len(textSpecs) >= nTexts and textFillRatio >= limit:
                            finished = True
                            break
                    if finished:
                        break

                #spacing, values = tickLevels[best]
                #strings = self.tickStrings(values, self.scale, spacing)
                # Determine exactly where tick text should be drawn
                for j in range(len(strings)):
                    vstr = strings[j]
                    if vstr is None: ## this tick was ignored because it is out of bounds
                        continue
                    vstr = asUnicode(vstr)
                    x = tickPositions[i][j]
                    #textRect = p.boundingRect(QtCore.QRectF(0, 0, 100, 100), QtCore.Qt.AlignCenter, vstr)
                    textRect = rects[j]
                    height = textRect.height()
                    width = textRect.width()
                    #self.textHeight = height
                    offset = max(0,self.style['tickLength']) + textOffset
                    if self.orientation == 'left':
                        textFlags = QtCore.Qt.TextDontClip|QtCore.Qt.AlignRight|QtCore.Qt.AlignVCenter
                        rect = QtCore.QRectF(tickStop-offset-width, x-(height/2), width, height)
                    elif self.orientation == 'right':
                        textFlags = QtCore.Qt.TextDontClip|QtCore.Qt.AlignLeft|QtCore.Qt.AlignVCenter
                        rect = QtCore.QRectF(tickStop+offset, x-(height/2), width, height)
                    elif self.orientation == 'top':
                        textFlags = QtCore.Qt.TextDontClip|QtCore.Qt.AlignCenter|QtCore.Qt.AlignBottom
                        rect = QtCore.QRectF(x-width/2., tickStop-offset-height, width, height)
                    elif self.orientation == 'bottom':
                        textFlags = QtCore.Qt.TextDontClip|QtCore.Qt.AlignCenter|QtCore.Qt.AlignTop
                        rect = QtCore.QRectF(x-width/2., tickStop+offset, width, height)

                    #p.setPen(self.pen())
                    #p.drawText(rect, textFlags, vstr)
                    textSpecs.append((rect, textFlags, vstr))
            profiler('compute text')

            ## update max text size if needed.
            self._updateMaxTextSize(textSize2)

            return (axisSpec, tickSpecs, textSpecs)

        def drawPicture(self, p, axisSpec, tickSpecs, textSpecs):
            profiler = debug.Profiler()

            p.setRenderHint(p.Antialiasing, False)
            p.setRenderHint(p.TextAntialiasing, True)

            ## draw long line along axis
            pen, p1, p2 = axisSpec
            p.setPen(pen)
            p.drawLine(p1, p2)
            p.translate(0.5,0)  ## resolves some damn pixel ambiguity

            ## draw ticks
            for pen, p1, p2 in tickSpecs:
                p.setPen(pen)
                p.drawLine(p1, p2)
            profiler('draw ticks')

            ## Draw all text
            if self.tickFont is not None:
                p.setFont(self.tickFont)
            p.setPen(self.pen())
            for rect, flags, text in textSpecs:
                p.drawText(rect, flags, text)
                #p.drawRect(rect)
            profiler('draw text')

        def show(self):
            GraphicsWidget.show(self)
            if self.orientation in ['left', 'right']:
                self._updateWidth()
            else:
                self._updateHeight()

        def hide(self):
            GraphicsWidget.hide(self)
            if self.orientation in ['left', 'right']:
                self._updateWidth()
            else:
                self._updateHeight()

        def wheelEvent(self, ev):
            if self.linkedView() is None:
                return
            if self.orientation in ['left', 'right']:
                self.linkedView().wheelEvent(ev, axis=1)
            else:
                self.linkedView().wheelEvent(ev, axis=0)
            ev.accept()

        def mouseDragEvent(self, event):
            if self.linkedView() is None:
                return
            if self.orientation in ['left', 'right']:
                return self.linkedView().mouseDragEvent(event, axis=1)
            else:
                return self.linkedView().mouseDragEvent(event, axis=0)

        def mouseClickEvent(self, event):
            if self.linkedView() is None:
                return
            return self.linkedView().mouseClickEvent(event)