biopython/Bio/Graphics/GenomeDiagram/_LinearDrawer.py

# Copyright 2003-2008 by Leighton Pritchard.  All rights reserved.
# Revisions copyright 2008-2009 by Peter Cock.
#
# This file is part of the Biopython distribution and governed by your
# choice of the "Biopython License Agreement" or the "BSD 3-Clause License".
# Please see the LICENSE file that should have been included as part of this
# package.
#
# Contact:       Leighton Pritchard, The James Hutton Institute,
#                Invergowrie, Dundee, Scotland, DD2 5DA, UK
#                Leighton.Pritchard@hutton.ac.uk
################################################################################

"""Linear Drawer module.

Provides:
 - LinearDrawer -  Drawing object for linear diagrams

For drawing capabilities, this module uses reportlab to draw and write
the diagram: http://www.reportlab.com
"""

# ReportLab imports

from math import ceil

from reportlab.graphics.shapes import Drawing
from reportlab.graphics.shapes import Group
from reportlab.graphics.shapes import Line
from reportlab.graphics.shapes import Polygon
from reportlab.graphics.shapes import String
from reportlab.lib import colors

from ._AbstractDrawer import _stroke_and_fill_colors

# GenomeDiagram imports
from ._AbstractDrawer import AbstractDrawer
from ._AbstractDrawer import angle2trig
from ._AbstractDrawer import deduplicate
from ._AbstractDrawer import draw_arrow
from ._AbstractDrawer import draw_box
from ._AbstractDrawer import draw_cut_corner_box
from ._AbstractDrawer import intermediate_points
from ._FeatureSet import FeatureSet
from ._GraphSet import GraphSet


class LinearDrawer(AbstractDrawer):
    """Linear Drawer.

    Inherits from:
     - AbstractDrawer

    Attributes:
     - tracklines    Boolean for whether to draw lines delineating tracks
     - pagesize      Tuple describing the size of the page in pixels
     - x0            Float X co-ord for leftmost point of drawable area
     - xlim          Float X co-ord for rightmost point of drawable area
     - y0            Float Y co-ord for lowest point of drawable area
     - ylim          Float Y co-ord for topmost point of drawable area
     - pagewidth     Float pixel width of drawable area
     - pageheight    Float pixel height of drawable area
     - xcenter       Float X co-ord of center of drawable area
     - ycenter       Float Y co-ord of center of drawable area
     - start         Int, base to start drawing from
     - end           Int, base to stop drawing at
     - length        Int, size of sequence to be drawn
     - fragments     Int, number of fragments into which to divide the
       drawn sequence
     - fragment_size Float (0->1) the proportion of the fragment height to
       draw in
     - track_size    Float (0->1) the proportion of the track height to
       draw in
     - drawing       Drawing canvas
     - drawn_tracks  List of ints denoting which tracks are to be drawn
     - current_track_level   Int denoting which track is currently being
       drawn
     - fragment_height   Float total fragment height in pixels
     - fragment_bases    Int total fragment length in bases
     - fragment_lines    Dictionary of top and bottom y-coords of fragment,
       keyed by fragment number
     - fragment_limits   Dictionary of start and end bases of each fragment,
       keyed by fragment number
     - track_offsets     Dictionary of number of pixels that each track top,
       center and bottom is offset from the base of a fragment, keyed by track
     - cross_track_links List of tuples each with four entries (track A,
       feature A, track B, feature B) to be linked.

    """

    def __init__(
        self,
        parent=None,
        pagesize="A3",
        orientation="landscape",
        x=0.05,
        y=0.05,
        xl=None,
        xr=None,
        yt=None,
        yb=None,
        start=None,
        end=None,
        tracklines=0,
        fragments=10,
        fragment_size=None,
        track_size=0.75,
        cross_track_links=None,
    ):
        """Initialize.

        Arguments:
         - parent    Diagram object containing the data that the drawer draws
         - pagesize  String describing the ISO size of the image, or a tuple
           of pixels
         - orientation   String describing the required orientation of the
           final drawing ('landscape' or 'portrait')
         - x         Float (0->1) describing the relative size of the X
           margins to the page
         - y         Float (0->1) describing the relative size of the Y
           margins to the page
         - xl        Float (0->1) describing the relative size of the left X
           margin to the page (overrides x)
         - xl        Float (0->1) describing the relative size of the left X
           margin to the page (overrides x)
         - xr        Float (0->1) describing the relative size of the right X
           margin to the page (overrides x)
         - yt        Float (0->1) describing the relative size of the top Y
           margin to the page (overrides y)
         - yb        Float (0->1) describing the relative size of the lower Y
           margin to the page (overrides y)
         - start     Int, the position to begin drawing the diagram at
         - end       Int, the position to stop drawing the diagram at
         - tracklines    Boolean flag to show (or not) lines delineating tracks
           on the diagram
         - fragments Int, the number of equal fragments into which the
           sequence should be divided for drawing
         - fragment_size Float(0->1) The proportion of the available height
           for the fragment that should be taken up in drawing
         - track_size    The proportion of the available track height that
           should be taken up in drawing
         - cross_track_links List of tuples each with four entries (track A,
           feature A, track B, feature B) to be linked.
        """
        # Use the superclass' instantiation method
        AbstractDrawer.__init__(
            self,
            parent,
            pagesize,
            orientation,
            x,
            y,
            xl,
            xr,
            yt,
            yb,
            start,
            end,
            tracklines,
            cross_track_links,
        )

        # Useful measurements on the page
        self.fragments = fragments
        if fragment_size is not None:
            self.fragment_size = fragment_size
        else:
            if self.fragments == 1:
                # For single fragments, default to full height
                self.fragment_size = 1
            else:
                # Otherwise keep a 10% gap between fragments
                self.fragment_size = 0.9
        self.track_size = track_size

    def draw(self):
        """Draw a linear diagram of the data in the parent Diagram object."""
        # Instantiate the drawing canvas
        self.drawing = Drawing(self.pagesize[0], self.pagesize[1])

        feature_elements = []  # holds feature elements
        feature_labels = []  # holds feature labels
        greytrack_bgs = []  # holds track background
        greytrack_labels = []  # holds track foreground labels
        scale_axes = []  # holds scale axes
        scale_labels = []  # holds scale axis labels

        # Get the tracks to be drawn
        self.drawn_tracks = self._parent.get_drawn_levels()

        # Set fragment and track sizes
        self.init_fragments()
        self.set_track_heights()

        # Go through each track in the parent (if it is to be drawn) one by
        # one and collate the data as drawing elements
        for track_level in self.drawn_tracks:  # only use tracks to be drawn
            self.current_track_level = track_level  # establish track level
            track = self._parent[track_level]  # get the track at that level
            gbgs, glabels = self.draw_greytrack(track)  # get greytrack elements
            greytrack_bgs.append(gbgs)
            greytrack_labels.append(glabels)
            features, flabels = self.draw_track(track)  # get feature and graph elements
            feature_elements.append(features)
            feature_labels.append(flabels)
            if track.scale:
                axes, slabels = self.draw_scale(track)  # get scale elements
                scale_axes.append(axes)
                scale_labels.append(slabels)

        feature_cross_links = []
        for cross_link_obj in self.cross_track_links:
            cross_link_elements = self.draw_cross_link(cross_link_obj)
            if cross_link_elements:
                feature_cross_links.append(cross_link_elements)

        # Groups listed in order of addition to page (from back to front)
        # Draw track backgrounds
        # Draw feature cross track links
        # Draw features and graphs
        # Draw scale axes
        # Draw scale labels
        # Draw feature labels
        # Draw track labels
        element_groups = [
            greytrack_bgs,
            feature_cross_links,
            feature_elements,
            scale_axes,
            scale_labels,
            feature_labels,
            greytrack_labels,
        ]
        for element_group in element_groups:
            for element_list in element_group:
                [self.drawing.add(element) for element in element_list]

        if self.tracklines:  # Draw test tracks over top of diagram
            self.draw_test_tracks()

    def init_fragments(self):
        """Initialize useful values for positioning diagram elements."""
        # Set basic heights, lengths etc
        self.fragment_height = self.pageheight / self.fragments
        # total fragment height in pixels
        self.fragment_bases = ceil(self.length / self.fragments)
        # fragment length in bases

        # Key fragment base and top lines by fragment number
        # Holds bottom and top line locations of fragments, keyed by fragment number
        self.fragment_lines = {}
        # Number of pixels to crop the fragment:
        fragment_crop = (1 - self.fragment_size) / 2
        fragy = self.ylim  # Holder for current absolute fragment base
        for fragment in range(self.fragments):
            fragtop = fragy - fragment_crop * self.fragment_height  # top - crop
            fragbtm = (
                fragy - (1 - fragment_crop) * self.fragment_height
            )  # bottom + crop
            self.fragment_lines[fragment] = (fragbtm, fragtop)
            fragy -= self.fragment_height  # next fragment base

        # Key base starts and ends for each fragment by fragment number
        self.fragment_limits = {}  # Holds first and last base positions in a fragment
        fragment_step = self.fragment_bases  # bases per fragment
        fragment_count = 0
        # Add start and end positions for each fragment to dictionary
        for marker in range(int(self.start), int(self.end), int(fragment_step)):
            self.fragment_limits[fragment_count] = (marker, marker + fragment_step)
            fragment_count += 1

    def set_track_heights(self):
        """Set track heights.

        Since tracks may not be of identical heights, the bottom and top
        offsets of each track relative to the fragment top and bottom is
        stored in a dictionary - self.track_offsets, keyed by track number.
        """
        bot_track = min(min(self.drawn_tracks), 1)
        top_track = max(self.drawn_tracks)  # The 'highest' track number to draw

        trackunit_sum = 0  # Total number of 'units' for the tracks
        trackunits = {}  # The start and end units for each track, keyed by track number
        heightholder = 0  # placeholder variable
        for track in range(bot_track, top_track + 1):  # for all track numbers to 'draw'
            try:
                trackheight = self._parent[track].height  # Get track height
            except Exception:  # TODO: IndexError?
                trackheight = 1  # ...or default to 1
            trackunit_sum += trackheight  # increment total track unit height
            trackunits[track] = (heightholder, heightholder + trackheight)
            heightholder += trackheight  # move to next height
        trackunit_height = self.fragment_height * self.fragment_size / trackunit_sum

        # Calculate top and bottom offsets for each track, relative to fragment
        # base
        track_offsets = {}  # The offsets from fragment base for each track
        track_crop = (
            trackunit_height * (1 - self.track_size) / 2.0
        )  # 'step back' in pixels
        assert track_crop >= 0
        for track in trackunits:
            top = trackunits[track][1] * trackunit_height - track_crop  # top offset
            btm = trackunits[track][0] * trackunit_height + track_crop  # bottom offset
            ctr = btm + (top - btm) / 2.0  # center offset
            track_offsets[track] = (btm, ctr, top)
        self.track_offsets = track_offsets

    def draw_test_tracks(self):
        """Draw test tracks.

        Draw red lines indicating the top and bottom of each fragment,
        and blue ones indicating tracks to be drawn.
        """
        # Add lines for each fragment
        for fbtm, ftop in self.fragment_lines.values():
            self.drawing.add(
                Line(self.x0, ftop, self.xlim, ftop, strokeColor=colors.red)
            )  # top line
            self.drawing.add(
                Line(self.x0, fbtm, self.xlim, fbtm, strokeColor=colors.red)
            )  # bottom line

            # Add track lines for this fragment - but only for drawn tracks
            for track in self.drawn_tracks:
                trackbtm = fbtm + self.track_offsets[track][0]
                trackctr = fbtm + self.track_offsets[track][1]
                tracktop = fbtm + self.track_offsets[track][2]
                self.drawing.add(
                    Line(
                        self.x0, tracktop, self.xlim, tracktop, strokeColor=colors.blue
                    )
                )  # top line
                self.drawing.add(
                    Line(
                        self.x0, trackctr, self.xlim, trackctr, strokeColor=colors.green
                    )
                )  # center line
                self.drawing.add(
                    Line(
                        self.x0, trackbtm, self.xlim, trackbtm, strokeColor=colors.blue
                    )
                )  # bottom line

    def draw_track(self, track):
        """Draw track.

        Arguments:
         - track     Track object

        Returns a tuple (list of elements in the track, list of labels in
        the track).
        """
        track_elements = []  # Holds elements from features and graphs
        track_labels = []  # Holds labels from features and graphs

        # Distribution dictionary for dealing with different set types
        set_methods = {FeatureSet: self.draw_feature_set, GraphSet: self.draw_graph_set}

        for set in track.get_sets():  # Draw the feature or graph sets
            elements, labels = set_methods[set.__class__](set)
            track_elements += elements
            track_labels += labels
        return track_elements, track_labels

    def draw_tick(self, tickpos, ctr, ticklen, track, draw_label):
        """Draw tick.

        Arguments:
         - tickpos   Int, position of the tick on the sequence
         - ctr       Float, Y co-ord of the center of the track
         - ticklen   How long to draw the tick
         - track     Track, the track the tick is drawn on
         - draw_label    Boolean, write the tick label?

        Returns a drawing element that is the tick on the scale
        """
        if self.start >= tickpos and tickpos >= self.end:
            raise RuntimeError(
                "Tick at %i, but showing %i to %i" % (tickpos, self.start, self.end)
            )
        if not (
            (track.start is None or track.start <= tickpos)
            and (track.end is None or tickpos <= track.end)
        ):
            raise RuntimeError(
                "Tick at %i, but showing %r to %r for track"
                % (tickpos, track.start, track.end)
            )
        fragment, tickx = self.canvas_location(tickpos)  # Tick coordinates
        assert fragment >= 0, "Fragment %i, tickpos %i" % (fragment, tickpos)
        tctr = ctr + self.fragment_lines[fragment][0]  # Center line of the track
        tickx += self.x0  # Tick X co-ord
        ticktop = tctr + ticklen  # Y co-ord of tick top
        tick = Line(tickx, tctr, tickx, ticktop, strokeColor=track.scale_color)
        if draw_label:  # Put tick position on as label
            if track.scale_format == "SInt":
                if tickpos >= 1000000:
                    tickstring = str(tickpos // 1000000) + " Mbp"
                elif tickpos >= 1000:
                    tickstring = str(tickpos // 1000) + " Kbp"
                else:
                    tickstring = str(tickpos)
            else:
                tickstring = str(tickpos)
            label = String(
                0,
                0,
                tickstring,  # Make label string
                fontName=track.scale_font,
                fontSize=track.scale_fontsize,
                fillColor=track.scale_color,
            )
            labelgroup = Group(label)
            rotation = angle2trig(track.scale_fontangle)
            labelgroup.transform = (
                rotation[0],
                rotation[1],
                rotation[2],
                rotation[3],
                tickx,
                ticktop,
            )
        else:
            labelgroup = None
        return tick, labelgroup

    def draw_scale(self, track):
        """Draw scale.

        Argument:
         - track     Track object

        Returns a tuple of (list of elements in the scale, list of labels
        in the scale).
        """
        scale_elements = []  # Holds axes and ticks
        scale_labels = []  # Holds labels

        if not track.scale:  # No scale required, exit early
            return [], []

        # Get track location
        btm, ctr, top = self.track_offsets[self.current_track_level]
        trackheight = top - ctr

        # For each fragment, draw the scale for this track
        start, end = self._current_track_start_end()
        start_f, start_x = self.canvas_location(start)
        end_f, end_x = self.canvas_location(end)

        for fragment in range(start_f, end_f + 1):
            tbtm = btm + self.fragment_lines[fragment][0]
            tctr = ctr + self.fragment_lines[fragment][0]
            ttop = top + self.fragment_lines[fragment][0]
            # X-axis
            if fragment == start_f:
                x_left = start_x
            else:
                x_left = 0
            if fragment == end_f:
                x_right = end_x
                # Y-axis end marker
                scale_elements.append(
                    Line(
                        self.x0 + x_right,
                        tbtm,
                        self.x0 + x_right,
                        ttop,
                        strokeColor=track.scale_color,
                    )
                )
            else:
                x_right = self.xlim - self.x0
            scale_elements.append(
                Line(
                    self.x0 + x_left,
                    tctr,
                    self.x0 + x_right,
                    tctr,
                    strokeColor=track.scale_color,
                )
            )
            # Y-axis start marker
            scale_elements.append(
                Line(
                    self.x0 + x_left,
                    tbtm,
                    self.x0 + x_left,
                    ttop,
                    strokeColor=track.scale_color,
                )
            )

        start, end = self._current_track_start_end()
        if track.scale_ticks:  # Ticks are required on the scale
            # Draw large ticks
            # I want the ticks to be consistently positioned relative to
            # the start of the sequence (position 0), not relative to the
            # current viewpoint (self.start and self.end)

            ticklen = track.scale_largeticks * trackheight
            tickiterval = int(track.scale_largetick_interval)
            # Note that we could just start the list of ticks using
            # range(0,self.end,tickinterval) and the filter out the
            # ones before self.start - but this seems wasteful.
            # Using tickiterval * (self.start//tickiterval) is a shortcut.
            for tickpos in range(
                tickiterval * (self.start // tickiterval), int(self.end), tickiterval
            ):
                if tickpos <= start or end <= tickpos:
                    continue
                tick, label = self.draw_tick(
                    tickpos, ctr, ticklen, track, track.scale_largetick_labels
                )
                scale_elements.append(tick)
                if label is not None:  # If there's a label, add it
                    scale_labels.append(label)
            # Draw small ticks
            ticklen = track.scale_smallticks * trackheight
            tickiterval = int(track.scale_smalltick_interval)
            for tickpos in range(
                tickiterval * (self.start // tickiterval), int(self.end), tickiterval
            ):
                if tickpos <= start or end <= tickpos:
                    continue
                tick, label = self.draw_tick(
                    tickpos, ctr, ticklen, track, track.scale_smalltick_labels
                )
                scale_elements.append(tick)
                if label is not None:  # If there's a label, add it
                    scale_labels.append(label)

        # Check to see if the track contains a graph - if it does, get the
        # minimum and maximum values, and put them on the scale Y-axis
        if track.axis_labels:
            for set in track.get_sets():  # Check all sets...
                if set.__class__ is GraphSet:  # ...for a graph set
                    graph_label_min = []
                    graph_label_mid = []
                    graph_label_max = []
                    for graph in set.get_graphs():
                        quartiles = graph.quartiles()
                        minval, maxval = quartiles[0], quartiles[4]
                        if graph.center is None:
                            midval = (maxval + minval) / 2.0
                            graph_label_min.append(f"{minval:.3f}")
                            graph_label_max.append(f"{maxval:.3f}")
                        else:
                            diff = max((graph.center - minval), (maxval - graph.center))
                            minval = graph.center - diff
                            maxval = graph.center + diff
                            midval = graph.center
                            graph_label_mid.append(f"{midval:.3f}")
                            graph_label_min.append(f"{minval:.3f}")
                            graph_label_max.append(f"{maxval:.3f}")
                    for fragment in range(
                        start_f, end_f + 1
                    ):  # Add to all used fragment axes
                        tbtm = btm + self.fragment_lines[fragment][0]
                        tctr = ctr + self.fragment_lines[fragment][0]
                        ttop = top + self.fragment_lines[fragment][0]
                        if fragment == start_f:
                            x_left = start_x
                        else:
                            x_left = 0
                        for val, pos in [
                            (";".join(graph_label_min), tbtm),
                            (";".join(graph_label_max), ttop),
                            (";".join(graph_label_mid), tctr),
                        ]:
                            label = String(
                                0,
                                0,
                                val,
                                fontName=track.scale_font,
                                fontSize=track.scale_fontsize,
                                fillColor=track.scale_color,
                            )
                            labelgroup = Group(label)
                            rotation = angle2trig(track.scale_fontangle)
                            labelgroup.transform = (
                                rotation[0],
                                rotation[1],
                                rotation[2],
                                rotation[3],
                                self.x0 + x_left,
                                pos,
                            )
                            scale_labels.append(labelgroup)

        return scale_elements, scale_labels

    def draw_greytrack(self, track):
        """Draw greytrack.

        Arguments:
         - track     Track object

        Put in a grey background to the current track in all fragments,
        if track specifies that we should.
        """
        greytrack_bgs = []  # Holds grey track backgrounds
        greytrack_labels = []  # Holds grey foreground labels

        if not track.greytrack:  # No greytrack required, return early
            return [], []

        # Get track location
        btm, ctr, top = self.track_offsets[self.current_track_level]

        start, end = self._current_track_start_end()
        start_fragment, start_offset = self.canvas_location(start)
        end_fragment, end_offset = self.canvas_location(end)

        # Add greytrack to all fragments for this track
        for fragment in range(start_fragment, end_fragment + 1):
            tbtm = btm + self.fragment_lines[fragment][0]
            tctr = ctr + self.fragment_lines[fragment][0]
            ttop = top + self.fragment_lines[fragment][0]
            if fragment == start_fragment:
                x1 = self.x0 + start_offset
            else:
                x1 = self.x0
            if fragment == end_fragment:
                x2 = self.x0 + end_offset
            else:
                x2 = self.xlim
            box = draw_box(
                (x1, tbtm),
                (x2, ttop),
                colors.Color(0.96, 0.96, 0.96),  # Grey track bg
            )  # is just a box
            greytrack_bgs.append(box)

            if track.greytrack_labels:  # If labels are required
                # # how far apart should they be?
                labelstep = self.pagewidth / track.greytrack_labels
                label = String(
                    0,
                    0,
                    track.name,  # label contents
                    fontName=track.greytrack_font,
                    fontSize=track.greytrack_fontsize,
                    fillColor=track.greytrack_fontcolor,
                )
                # Create a new labelgroup at each position the label is required
                for x in range(int(self.x0), int(self.xlim), int(labelstep)):
                    if fragment == start_fragment and x < start_offset:
                        continue
                    if (
                        fragment == end_fragment
                        and end_offset < x + label.getBounds()[2]
                    ):
                        continue
                    labelgroup = Group(label)
                    rotation = angle2trig(track.greytrack_font_rotation)
                    labelgroup.transform = (
                        rotation[0],
                        rotation[1],
                        rotation[2],
                        rotation[3],
                        x,
                        tbtm,
                    )
                    if not self.xlim - x <= labelstep:
                        # Don't overlap the end of the track
                        greytrack_labels.append(labelgroup)

        return greytrack_bgs, greytrack_labels

    def draw_feature_set(self, set):
        """Draw feature set.

        Arguments:
         - set       FeatureSet object

        Returns a tuple (list of elements describing features, list of
        labels for elements).
        """
        # print("draw feature set")
        feature_elements = []  # Holds diagram elements belonging to the features
        label_elements = []  # Holds diagram elements belonging to feature labels

        # Collect all the elements for the feature set
        for feature in set.get_features():
            if self.is_in_bounds(feature.start) or self.is_in_bounds(feature.end):
                features, labels = self.draw_feature(feature)  # get elements and labels
                feature_elements += features
                label_elements += labels

        return feature_elements, label_elements

    def draw_feature(self, feature):
        """Draw feature.

        Arguments:
         - feature           Feature containing location info

        Returns tuple of (list of elements describing single feature, list
        of labels for those elements).
        """
        if feature.hide:  # Feature hidden, don't draw it...
            return [], []

        feature_elements = []  # Holds diagram elements belonging to the feature
        label_elements = []  # Holds labels belonging to the feature

        start, end = self._current_track_start_end()
        # A single feature may be split into subfeatures, so loop over them
        for locstart, locend in feature.locations:
            if locend < start:
                continue
            locstart = max(locstart, start)
            if end < locstart:
                continue
            locend = min(locend, end)
            feature_boxes = self.draw_feature_location(feature, locstart, locend)
            for box, label in feature_boxes:
                feature_elements.append(box)
                if label is not None:
                    label_elements.append(label)

        return feature_elements, label_elements

    def draw_feature_location(self, feature, locstart, locend):
        """Draw feature location."""
        feature_boxes = []
        # Get start and end positions for feature/subfeatures
        start_fragment, start_offset = self.canvas_location(locstart)
        end_fragment, end_offset = self.canvas_location(locend)
        # print("start_fragment, start_offset", start_fragment, start_offset)
        # print("end_fragment, end_offset", end_fragment, end_offset)
        # print("start, end", locstart, locend)

        # Note that there is a strange situation where a feature may be in
        # several parts, and one or more of those parts may end up being
        # drawn on a non-existent fragment.  So we check that the start and
        # end fragments do actually exist in terms of the drawing
        allowed_fragments = list(self.fragment_limits.keys())
        if start_fragment in allowed_fragments and end_fragment in allowed_fragments:
            # print(feature.name, feature.start, feature.end, start_offset, end_offset)
            if start_fragment == end_fragment:  # Feature is found on one fragment
                feature_box, label = self.get_feature_sigil(
                    feature, start_offset, end_offset, start_fragment
                )
                feature_boxes.append((feature_box, label))
                # feature_elements.append(feature_box)
                # if label is not None:   # There is a label for the feature
                #    label_elements.append(label)
            else:  # Feature is split over two or more fragments
                fragment = start_fragment
                start = start_offset
                # The bit that runs up to the end of the first fragment,
                # and any bits that subsequently span whole fragments
                while self.fragment_limits[fragment][1] < locend:
                    # print(fragment, self.fragment_limits[fragment][1], locend)
                    feature_box, label = self.get_feature_sigil(
                        feature, start, self.pagewidth, fragment
                    )

                    fragment += 1  # move to next fragment
                    start = 0  # start next sigil from start of fragment
                    feature_boxes.append((feature_box, label))
                    # feature_elements.append(feature_box)
                    # if label is not None:   # There's a label for the feature
                    #    label_elements.append(label)
                # The last bit of the feature
                # print(locend, self.end, fragment)
                # print(self.fragment_bases, self.length)
                feature_box, label = self.get_feature_sigil(
                    feature, 0, end_offset, fragment
                )
                feature_boxes.append((feature_box, label))
        # if locstart > locend:
        #    print(locstart, locend, feature.location.strand, feature_boxes, feature.name)
        return feature_boxes

    def draw_cross_link(self, cross_link):
        """Draw cross-link between two features."""
        startA = cross_link.startA
        startB = cross_link.startB
        endA = cross_link.endA
        endB = cross_link.endB

        if not self.is_in_bounds(startA) and not self.is_in_bounds(endA):
            return None
        if not self.is_in_bounds(startB) and not self.is_in_bounds(endB):
            return None

        if startA < self.start:
            startA = self.start
        if startB < self.start:
            startB = self.start
        if self.end < endA:
            endA = self.end
        if self.end < endB:
            endB = self.end

        trackobjA = cross_link._trackA(list(self._parent.tracks.values()))
        trackobjB = cross_link._trackB(list(self._parent.tracks.values()))
        assert trackobjA is not None
        assert trackobjB is not None
        if trackobjA == trackobjB:
            raise NotImplementedError

        if trackobjA.start is not None:
            if endA < trackobjA.start:
                return
            startA = max(startA, trackobjA.start)
        if trackobjA.end is not None:
            if trackobjA.end < startA:
                return
            endA = min(endA, trackobjA.end)
        if trackobjB.start is not None:
            if endB < trackobjB.start:
                return
            startB = max(startB, trackobjB.start)
        if trackobjB.end is not None:
            if trackobjB.end < startB:
                return
            endB = min(endB, trackobjB.end)

        for track_level in self._parent.get_drawn_levels():
            track = self._parent[track_level]
            if track == trackobjA:
                trackA = track_level
            if track == trackobjB:
                trackB = track_level
        if trackA == trackB:
            raise NotImplementedError

        strokecolor, fillcolor = _stroke_and_fill_colors(
            cross_link.color, cross_link.border
        )

        allowed_fragments = list(self.fragment_limits.keys())

        start_fragmentA, start_offsetA = self.canvas_location(startA)
        end_fragmentA, end_offsetA = self.canvas_location(endA)
        if (
            start_fragmentA not in allowed_fragments
            or end_fragmentA not in allowed_fragments
        ):
            return

        start_fragmentB, start_offsetB = self.canvas_location(startB)
        end_fragmentB, end_offsetB = self.canvas_location(endB)
        if (
            start_fragmentB not in allowed_fragments
            or end_fragmentB not in allowed_fragments
        ):
            return

        # TODO - Better drawing of flips when split between fragments

        answer = []
        for fragment in range(
            min(start_fragmentA, start_fragmentB), max(end_fragmentA, end_fragmentB) + 1
        ):
            btmA, ctrA, topA = self.track_offsets[trackA]
            btmA += self.fragment_lines[fragment][0]
            ctrA += self.fragment_lines[fragment][0]
            topA += self.fragment_lines[fragment][0]

            btmB, ctrB, topB = self.track_offsets[trackB]
            btmB += self.fragment_lines[fragment][0]
            ctrB += self.fragment_lines[fragment][0]
            topB += self.fragment_lines[fragment][0]

            if self.fragment_limits[fragment][1] < endA:
                xAe = self.x0 + self.pagewidth
                crop_rightA = True
            else:
                xAe = self.x0 + end_offsetA
                crop_rightA = False
            if self.fragment_limits[fragment][1] < endB:
                xBe = self.x0 + self.pagewidth
                crop_rightB = True
            else:
                xBe = self.x0 + end_offsetB
                crop_rightB = False

            if fragment < start_fragmentA:
                xAs = self.x0 + self.pagewidth
                xAe = xAs
                crop_leftA = False
            elif fragment == start_fragmentA:
                xAs = self.x0 + start_offsetA
                crop_leftA = False
            else:
                xAs = self.x0
                crop_leftA = True

            if fragment < start_fragmentB:
                xBs = self.x0 + self.pagewidth
                xBe = xBs
                crop_leftB = False
            elif fragment == start_fragmentB:
                xBs = self.x0 + start_offsetB
                crop_leftB = False
            else:
                xBs = self.x0
                crop_leftB = True

            if ctrA < ctrB:
                yA = topA
                yB = btmB
            else:
                yA = btmA
                yB = topB

            if fragment < start_fragmentB or end_fragmentB < fragment:
                if cross_link.flip:
                    # Just draw A as a triangle to left/right
                    if fragment < start_fragmentB:
                        extra = [self.x0 + self.pagewidth, 0.5 * (yA + yB)]
                    else:
                        extra = [self.x0, 0.5 * (yA + yB)]
                else:
                    if fragment < start_fragmentB:
                        extra = [
                            self.x0 + self.pagewidth,
                            0.7 * yA + 0.3 * yB,
                            self.x0 + self.pagewidth,
                            0.3 * yA + 0.7 * yB,
                        ]
                    else:
                        extra = [
                            self.x0,
                            0.3 * yA + 0.7 * yB,
                            self.x0,
                            0.7 * yA + 0.3 * yB,
                        ]
                answer.append(
                    Polygon(
                        deduplicate([xAs, yA, xAe, yA] + extra),
                        strokeColor=strokecolor,
                        fillColor=fillcolor,
                        # default is mitre/miter which can stick out too much:
                        strokeLineJoin=1,  # 1=round
                        strokewidth=0,
                    )
                )
            elif fragment < start_fragmentA or end_fragmentA < fragment:
                if cross_link.flip:
                    # Just draw B as a triangle to left
                    if fragment < start_fragmentA:
                        extra = [self.x0 + self.pagewidth, 0.5 * (yA + yB)]
                    else:
                        extra = [self.x0, 0.5 * (yA + yB)]
                else:
                    if fragment < start_fragmentA:
                        extra = [
                            self.x0 + self.pagewidth,
                            0.3 * yA + 0.7 * yB,
                            self.x0 + self.pagewidth,
                            0.7 * yA + 0.3 * yB,
                        ]
                    else:
                        extra = [
                            self.x0,
                            0.7 * yA + 0.3 * yB,
                            self.x0,
                            0.3 * yA + 0.7 * yB,
                        ]
                answer.append(
                    Polygon(
                        deduplicate([xBs, yB, xBe, yB] + extra),
                        strokeColor=strokecolor,
                        fillColor=fillcolor,
                        # default is mitre/miter which can stick out too much:
                        strokeLineJoin=1,  # 1=round
                        strokewidth=0,
                    )
                )
            elif cross_link.flip and (
                (crop_leftA and not crop_rightA) or (crop_leftB and not crop_rightB)
            ):
                # On left end of fragment... force "crossing" to margin
                answer.append(
                    Polygon(
                        deduplicate(
                            [
                                xAs,
                                yA,
                                xAe,
                                yA,
                                self.x0,
                                0.5 * (yA + yB),
                                xBe,
                                yB,
                                xBs,
                                yB,
                            ]
                        ),
                        strokeColor=strokecolor,
                        fillColor=fillcolor,
                        # default is mitre/miter which can stick out too much:
                        strokeLineJoin=1,  # 1=round
                        strokewidth=0,
                    )
                )
            elif cross_link.flip and (
                (crop_rightA and not crop_leftA) or (crop_rightB and not crop_leftB)
            ):
                # On right end... force "crossing" to margin
                answer.append(
                    Polygon(
                        deduplicate(
                            [
                                xAs,
                                yA,
                                xAe,
                                yA,
                                xBe,
                                yB,
                                xBs,
                                yB,
                                self.x0 + self.pagewidth,
                                0.5 * (yA + yB),
                            ]
                        ),
                        strokeColor=strokecolor,
                        fillColor=fillcolor,
                        # default is mitre/miter which can stick out too much:
                        strokeLineJoin=1,  # 1=round
                        strokewidth=0,
                    )
                )
            elif cross_link.flip:
                answer.append(
                    Polygon(
                        deduplicate([xAs, yA, xAe, yA, xBs, yB, xBe, yB]),
                        strokeColor=strokecolor,
                        fillColor=fillcolor,
                        # default is mitre/miter which can stick out too much:
                        strokeLineJoin=1,  # 1=round
                        strokewidth=0,
                    )
                )
            else:
                answer.append(
                    Polygon(
                        deduplicate([xAs, yA, xAe, yA, xBe, yB, xBs, yB]),
                        strokeColor=strokecolor,
                        fillColor=fillcolor,
                        # default is mitre/miter which can stick out too much:
                        strokeLineJoin=1,  # 1=round
                        strokewidth=0,
                    )
                )
        return answer

    def get_feature_sigil(self, feature, x0, x1, fragment, **kwargs):
        """Get feature sigil.

        Arguments:
         - feature       Feature object
         - x0            Start X coordinate on diagram
         - x1            End X coordinate on diagram
         - fragment      The fragment on which the feature appears

        Returns a drawable indicator of the feature, and any required label
        for it.
        """
        # Establish coordinates for drawing
        x0, x1 = self.x0 + x0, self.x0 + x1
        btm, ctr, top = self.track_offsets[self.current_track_level]
        try:
            btm += self.fragment_lines[fragment][0]
            ctr += self.fragment_lines[fragment][0]
            top += self.fragment_lines[fragment][0]
        except Exception:  # Only called if the method screws up big time
            print("We've got a screw-up")
            print(f"{self.start} {self.end}")
            print(self.fragment_bases)
            print(f"{x0!r} {x1!r}")
            for locstart, locend in feature.locations:
                print(self.canvas_location(locstart))
                print(self.canvas_location(locend))
            print(f"FEATURE\n{feature}")
            raise

        # Distribution dictionary for various ways of drawing the feature
        draw_methods = {
            "BOX": self._draw_sigil_box,
            "ARROW": self._draw_sigil_arrow,
            "BIGARROW": self._draw_sigil_big_arrow,
            "OCTO": self._draw_sigil_octo,
            "JAGGY": self._draw_sigil_jaggy,
        }

        method = draw_methods[feature.sigil]
        kwargs["head_length_ratio"] = feature.arrowhead_length
        kwargs["shaft_height_ratio"] = feature.arrowshaft_height

        # Support for clickable links... needs ReportLab 2.4 or later
        # which added support for links in SVG output.
        if hasattr(feature, "url"):
            kwargs["hrefURL"] = feature.url
            kwargs["hrefTitle"] = feature.name

        # Get sigil for the feature, give it the bounding box straddling
        # the axis (it decides strand specific placement)
        sigil = method(
            btm,
            ctr,
            top,
            x0,
            x1,
            strand=feature.location.strand,
            color=feature.color,
            border=feature.border,
            **kwargs,
        )

        if feature.label_strand:
            strand = feature.label_strand
        else:
            strand = feature.location.strand
        if feature.label:  # Feature requires a label
            label = String(
                0,
                0,
                feature.name,
                fontName=feature.label_font,
                fontSize=feature.label_size,
                fillColor=feature.label_color,
            )
            labelgroup = Group(label)
            # Feature is on top, or covers both strands (location affects
            # the height and rotation of the label)
            if strand != -1:
                rotation = angle2trig(feature.label_angle)
                if feature.label_position in ("end", "3'", "right"):
                    pos = x1
                elif feature.label_position in ("middle", "center", "centre"):
                    pos = (x1 + x0) / 2.0
                else:
                    # Default to start, i.e. 'start', "5'", 'left'
                    pos = x0
                labelgroup.transform = (
                    rotation[0],
                    rotation[1],
                    rotation[2],
                    rotation[3],
                    pos,
                    top,
                )
            else:  # Feature on bottom strand
                rotation = angle2trig(feature.label_angle + 180)
                if feature.label_position in ("end", "3'", "right"):
                    pos = x0
                elif feature.label_position in ("middle", "center", "centre"):
                    pos = (x1 + x0) / 2.0
                else:
                    # Default to start, i.e. 'start', "5'", 'left'
                    pos = x1
                labelgroup.transform = (
                    rotation[0],
                    rotation[1],
                    rotation[2],
                    rotation[3],
                    pos,
                    btm,
                )
        else:
            labelgroup = None
        return sigil, labelgroup

    def draw_graph_set(self, set):
        """Draw graph set.

        Arguments:
         - set       GraphSet object

        Returns tuple (list of graph elements, list of graph labels).
        """
        # print('draw graph set')
        elements = []  # Holds graph elements

        # Distribution dictionary for how to draw the graph
        style_methods = {
            "line": self.draw_line_graph,
            "heat": self.draw_heat_graph,
            "bar": self.draw_bar_graph,
        }

        for graph in set.get_graphs():
            elements += style_methods[graph.style](graph)

        return elements, []

    def draw_line_graph(self, graph):
        """Return a line graph as a list of drawable elements.

        Arguments:
         - graph     Graph object

        """
        # print('\tdraw_line_graph')
        line_elements = []  # Holds drawable elements

        # Get graph data
        data_quartiles = graph.quartiles()
        minval, maxval = data_quartiles[0], data_quartiles[4]
        btm, ctr, top = self.track_offsets[self.current_track_level]
        trackheight = 0.5 * (top - btm)
        datarange = maxval - minval
        if datarange == 0:
            datarange = trackheight

        start, end = self._current_track_start_end()
        data = graph[start:end]

        # midval is the value at which the x-axis is plotted, and is the
        # central ring in the track
        if graph.center is None:
            midval = (maxval + minval) / 2.0
        else:
            midval = graph.center
        # Whichever is the greatest difference: max-midval or min-midval, is
        # taken to specify the number of pixel units resolved along the
        # y-axis
        resolution = max((midval - minval), (maxval - midval))

        # Start from first data point
        pos, val = data[0]
        lastfrag, lastx = self.canvas_location(pos)
        lastx += self.x0  # Start xy co-ords
        lasty = (
            trackheight * (val - midval) / resolution
            + self.fragment_lines[lastfrag][0]
            + ctr
        )
        lastval = val
        # Add a series of lines linking consecutive data points
        for pos, val in data:
            frag, x = self.canvas_location(pos)
            x += self.x0  # next xy co-ords
            y = (
                trackheight * (val - midval) / resolution
                + self.fragment_lines[frag][0]
                + ctr
            )
            if frag == lastfrag:  # Points on the same fragment: draw the line
                line_elements.append(
                    Line(
                        lastx,
                        lasty,
                        x,
                        y,
                        strokeColor=graph.poscolor,
                        strokeWidth=graph.linewidth,
                    )
                )
            else:  # Points not on the same fragment, so interpolate
                tempy = (
                    trackheight * (val - midval) / resolution
                    + self.fragment_lines[lastfrag][0]
                    + ctr
                )
                line_elements.append(
                    Line(
                        lastx,
                        lasty,
                        self.xlim,
                        tempy,
                        strokeColor=graph.poscolor,
                        strokeWidth=graph.linewidth,
                    )
                )
                tempy = (
                    trackheight * (val - midval) / resolution
                    + self.fragment_lines[frag][0]
                    + ctr
                )
                line_elements.append(
                    Line(
                        self.x0,
                        tempy,
                        x,
                        y,
                        strokeColor=graph.poscolor,
                        strokeWidth=graph.linewidth,
                    )
                )
            lastfrag, lastx, lasty, lastval = frag, x, y, val

        return line_elements

    def draw_heat_graph(self, graph):
        """Return a list of drawable elements for the heat graph."""
        # print('\tdraw_heat_graph')
        # At each point contained in the graph data, we draw a box that is the
        # full height of the track, extending from the midpoint between the
        # previous and current data points to the midpoint between the current
        # and next data points
        heat_elements = []  # Holds drawable elements for the graph

        # Get graph data and information
        data_quartiles = graph.quartiles()
        minval, maxval = data_quartiles[0], data_quartiles[4]
        midval = (maxval + minval) / 2.0  # mid is the value at the X-axis
        btm, ctr, top = self.track_offsets[self.current_track_level]
        trackheight = top - btm

        start, end = self._current_track_start_end()
        data = intermediate_points(start, end, graph[start:end])

        if not data:
            return []

        # Create elements on the graph, indicating a large positive value by
        # the graph's poscolor, and a large negative value by the graph's
        # negcolor attributes
        for pos0, pos1, val in data:
            # assert start <= pos0 <= pos1 <= end
            fragment0, x0 = self.canvas_location(pos0)
            fragment1, x1 = self.canvas_location(pos1)
            x0, x1 = self.x0 + x0, self.x0 + x1  # account for margin
            # print('x1 before:', x1)

            # Calculate the heat color, based on the differential between
            # the value and the median value
            heat = colors.linearlyInterpolatedColor(
                graph.poscolor, graph.negcolor, maxval, minval, val
            )

            # Draw heat box
            if fragment0 == fragment1:  # Box is contiguous on one fragment
                if pos1 >= self.fragment_limits[fragment0][1]:
                    x1 = self.xlim
                ttop = top + self.fragment_lines[fragment0][0]
                tbtm = btm + self.fragment_lines[fragment0][0]
                # print('equal', pos0, pos1, val)
                # print(pos0, pos1, fragment0, fragment1)
                heat_elements.append(
                    draw_box((x0, tbtm), (x1, ttop), color=heat, border=None)
                )
            else:  # box is split over two or more fragments
                # if pos0 >= self.fragment_limits[fragment0][0]:
                #    fragment0 += 1
                fragment = fragment0
                start_x = x0
                while self.fragment_limits[fragment][1] <= pos1:
                    # print(pos0, self.fragment_limits[fragment][1], pos1)
                    ttop = top + self.fragment_lines[fragment][0]
                    tbtm = btm + self.fragment_lines[fragment][0]
                    heat_elements.append(
                        draw_box(
                            (start_x, tbtm), (self.xlim, ttop), color=heat, border=None
                        )
                    )
                    fragment += 1
                    start_x = self.x0
                ttop = top + self.fragment_lines[fragment][0]
                tbtm = btm + self.fragment_lines[fragment][0]
                # Add the last part of the bar
                # print('x1 after:', x1, '\n')
                heat_elements.append(
                    draw_box((self.x0, tbtm), (x1, ttop), color=heat, border=None)
                )

        return heat_elements

    def draw_bar_graph(self, graph):
        """Return list of drawable elements for a bar graph."""
        # print('\tdraw_bar_graph')
        # At each point contained in the graph data, we draw a vertical bar
        # from the track center to the height of the datapoint value (positive
        # values go up in one color, negative go down in the alternative
        # color).
        bar_elements = []  # Holds drawable elements for the graph

        # Set the number of pixels per unit for the data
        data_quartiles = graph.quartiles()
        minval, maxval = data_quartiles[0], data_quartiles[4]
        btm, ctr, top = self.track_offsets[self.current_track_level]
        trackheight = 0.5 * (top - btm)
        datarange = maxval - minval
        if datarange == 0:
            datarange = trackheight
        data = graph[self.start : self.end]
        # midval is the value at which the x-axis is plotted, and is the
        # central ring in the track
        if graph.center is None:
            midval = (maxval + minval) / 2.0
        else:
            midval = graph.center

        # Convert data into 'binned' blocks, covering half the distance to the
        # next data point on either side, accounting for the ends of fragments
        # and tracks
        start, end = self._current_track_start_end()
        data = intermediate_points(start, end, graph[start:end])

        if not data:
            return []

        # Whichever is the greatest difference: max-midval or min-midval, is
        # taken to specify the number of pixel units resolved along the
        # y-axis
        resolution = max((midval - minval), (maxval - midval))
        if resolution == 0:
            resolution = trackheight

        # Create elements for the bar graph based on newdata
        for pos0, pos1, val in data:
            fragment0, x0 = self.canvas_location(pos0)
            fragment1, x1 = self.canvas_location(pos1)
            x0, x1 = self.x0 + x0, self.x0 + x1  # account for margin
            barval = trackheight * (val - midval) / resolution
            if barval >= 0:  # Different colors for bars that extend above...
                barcolor = graph.poscolor
            else:  # ...or below the axis
                barcolor = graph.negcolor

            # Draw bar
            if fragment0 == fragment1:  # Box is contiguous
                if pos1 >= self.fragment_limits[fragment0][1]:
                    x1 = self.xlim
                tctr = ctr + self.fragment_lines[fragment0][0]
                barval += tctr
                bar_elements.append(draw_box((x0, tctr), (x1, barval), color=barcolor))
            else:  # Box is split over two or more fragments
                fragment = fragment0
                # if pos0 >= self.fragment_limits[fragment0][0]:
                #    fragment += 1
                start = x0
                while self.fragment_limits[fragment][1] < pos1:
                    tctr = ctr + self.fragment_lines[fragment][0]
                    thisbarval = barval + tctr
                    bar_elements.append(
                        draw_box((start, tctr), (self.xlim, thisbarval), color=barcolor)
                    )
                    fragment += 1
                    start = self.x0
                tctr = ctr + self.fragment_lines[fragment1][0]
                barval += tctr
                # Add the last part of the bar
                bar_elements.append(
                    draw_box((self.x0, tctr), (x1, barval), color=barcolor)
                )

        return bar_elements

    def canvas_location(self, base):
        """Canvas location of a base on the genome.

        Arguments:
         - base      The base number on the genome sequence

        Returns the x-coordinate and fragment number of a base on the
        genome sequence, in the context of the current drawing setup
        """
        base = int(base - self.start)  # number of bases we are from the start
        fragment = int(base / self.fragment_bases)
        if fragment < 1:  # First fragment
            base_offset = base
            fragment = 0
        elif fragment >= self.fragments:
            fragment = self.fragments - 1
            base_offset = self.fragment_bases
        else:  # Calculate number of bases from start of fragment
            base_offset = base % self.fragment_bases
        assert fragment < self.fragments, (
            base,
            self.start,
            self.end,
            self.length,
            self.fragment_bases,
        )
        # Calculate number of pixels from start of fragment
        x_offset = self.pagewidth * base_offset / self.fragment_bases
        return fragment, x_offset

    def _draw_sigil_box(self, bottom, center, top, x1, x2, strand, **kwargs):
        """Draw BOX sigil (PRIVATE)."""
        if strand == 1:
            y1 = center
            y2 = top
        elif strand == -1:
            y1 = bottom
            y2 = center
        else:
            y1 = bottom
            y2 = top
        return draw_box((x1, y1), (x2, y2), **kwargs)

    def _draw_sigil_octo(self, bottom, center, top, x1, x2, strand, **kwargs):
        """Draw OCTO sigil, a box with the corners cut off (PRIVATE)."""
        if strand == 1:
            y1 = center
            y2 = top
        elif strand == -1:
            y1 = bottom
            y2 = center
        else:
            y1 = bottom
            y2 = top
        return draw_cut_corner_box((x1, y1), (x2, y2), **kwargs)

    def _draw_sigil_jaggy(
        self, bottom, center, top, x1, x2, strand, color, border=None, **kwargs
    ):
        """Draw JAGGY sigil (PRIVATE).

        Although we may in future expose the head/tail jaggy lengths, for now
        both the left and right edges are drawn jagged.
        """
        if strand == 1:
            y1 = center
            y2 = top
            teeth = 2
        elif strand == -1:
            y1 = bottom
            y2 = center
            teeth = 2
        else:
            y1 = bottom
            y2 = top
            teeth = 4

        xmin = min(x1, x2)
        xmax = max(x1, x2)
        height = y2 - y1
        boxwidth = x2 - x1
        tooth_length = min(height / teeth, boxwidth * 0.5)

        headlength = tooth_length
        taillength = tooth_length

        strokecolor, color = _stroke_and_fill_colors(color, border)

        points = []
        for i in range(teeth):
            points.extend(
                (
                    xmin,
                    y1 + i * height / teeth,
                    xmin + taillength,
                    y1 + (i + 1) * height / teeth,
                )
            )
        for i in range(teeth):
            points.extend(
                (
                    xmax,
                    y1 + (teeth - i) * height / teeth,
                    xmax - headlength,
                    y1 + (teeth - i - 1) * height / teeth,
                )
            )

        return Polygon(
            deduplicate(points),
            strokeColor=strokecolor,
            strokeWidth=1,
            strokeLineJoin=1,  # 1=round
            fillColor=color,
            **kwargs,
        )

    def _draw_sigil_arrow(self, bottom, center, top, x1, x2, strand, **kwargs):
        """Draw ARROW sigil (PRIVATE)."""
        if strand == 1:
            y1 = center
            y2 = top
            orientation = "right"
        elif strand == -1:
            y1 = bottom
            y2 = center
            orientation = "left"
        else:
            y1 = bottom
            y2 = top
            orientation = "right"  # backward compatibility
        return draw_arrow((x1, y1), (x2, y2), orientation=orientation, **kwargs)

    def _draw_sigil_big_arrow(self, bottom, center, top, x1, x2, strand, **kwargs):
        """Draw BIGARROW sigil, like ARROW but straddles the axis (PRIVATE)."""
        if strand == -1:
            orientation = "left"
        else:
            orientation = "right"
        return draw_arrow((x1, bottom), (x2, top), orientation=orientation, **kwargs)