backend_svg.py

from collections import OrderedDict
import base64
import gzip
import hashlib
import io
import itertools
import logging
import re
import uuid

import numpy as np

from matplotlib import cbook, __version__, rcParams
from matplotlib.backend_bases import (
     _Backend, FigureCanvasBase, FigureManagerBase, RendererBase)
from matplotlib.backends.backend_mixed import MixedModeRenderer
from matplotlib.colors import rgb2hex
from matplotlib.font_manager import findfont, get_font
from matplotlib.ft2font import LOAD_NO_HINTING
from matplotlib.mathtext import MathTextParser
from matplotlib.path import Path
from matplotlib import _path
from matplotlib.transforms import Affine2D, Affine2DBase
from matplotlib import _png

_log = logging.getLogger(__name__)

backend_version = __version__

# ----------------------------------------------------------------------
# SimpleXMLWriter class
#
# Based on an original by Fredrik Lundh, but modified here to:
#   1. Support modern Python idioms
#   2. Remove encoding support (it's handled by the file writer instead)
#   3. Support proper indentation
#   4. Minify things a little bit

# --------------------------------------------------------------------
# The SimpleXMLWriter module is
#
# Copyright (c) 2001-2004 by Fredrik Lundh
#
# By obtaining, using, and/or copying this software and/or its
# associated documentation, you agree that you have read, understood,
# and will comply with the following terms and conditions:
#
# Permission to use, copy, modify, and distribute this software and
# its associated documentation for any purpose and without fee is
# hereby granted, provided that the above copyright notice appears in
# all copies, and that both that copyright notice and this permission
# notice appear in supporting documentation, and that the name of
# Secret Labs AB or the author not be used in advertising or publicity
# pertaining to distribution of the software without specific, written
# prior permission.
#
# SECRET LABS AB AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD
# TO THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANT-
# ABILITY AND FITNESS.  IN NO EVENT SHALL SECRET LABS AB OR THE AUTHOR
# BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY
# DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS,
# WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
# ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE
# OF THIS SOFTWARE.
# --------------------------------------------------------------------


def escape_cdata(s):
    s = s.replace("&", "&")
    s = s.replace("<", "&lt;")
    s = s.replace(">", "&gt;")
    return s


_escape_xml_comment = re.compile(r'-(?=-)')


def escape_comment(s):
    s = escape_cdata(s)
    return _escape_xml_comment.sub('- ', s)


def escape_attrib(s):
    s = s.replace("&", "&amp;")
    s = s.replace("'", "&apos;")
    s = s.replace('"', "&quot;")
    s = s.replace("<", "&lt;")
    s = s.replace(">", "&gt;")
    return s


def short_float_fmt(x):
    """
    Create a short string representation of a float, which is %f
    formatting with trailing zeros and the decimal point removed.
    """
    return '{0:f}'.format(x).rstrip('0').rstrip('.')


class XMLWriter:
    """
    Parameters
    ----------
    file : writable text file-like object
    """

    def __init__(self, file):
        self.__write = file.write
        if hasattr(file, "flush"):
            self.flush = file.flush
        self.__open = 0  # true if start tag is open
        self.__tags = []
        self.__data = []
        self.__indentation = " " * 64

    def __flush(self, indent=True):
        # flush internal buffers
        if self.__open:
            if indent:
                self.__write(">\n")
            else:
                self.__write(">")
            self.__open = 0
        if self.__data:
            data = ''.join(self.__data)
            self.__write(escape_cdata(data))
            self.__data = []

    def start(self, tag, attrib={}, **extra):
        """
        Opens a new element.  Attributes can be given as keyword
        arguments, or as a string/string dictionary. The method returns
        an opaque identifier that can be passed to the :meth:`close`
        method, to close all open elements up to and including this one.

        Parameters
        ----------
        tag
            Element tag.
        attrib
            Attribute dictionary.  Alternatively, attributes can be given as
            keyword arguments.

        Returns
        -------
        An element identifier.
        """
        self.__flush()
        tag = escape_cdata(tag)
        self.__data = []
        self.__tags.append(tag)
        self.__write(self.__indentation[:len(self.__tags) - 1])
        self.__write("<%s" % tag)
        for k, v in sorted({**attrib, **extra}.items()):
            if v:
                k = escape_cdata(k)
                v = escape_attrib(v)
                self.__write(' %s="%s"' % (k, v))
        self.__open = 1
        return len(self.__tags) - 1

    def comment(self, comment):
        """
        Adds a comment to the output stream.

        Parameters
        ----------
        comment : str
            Comment text.
        """
        self.__flush()
        self.__write(self.__indentation[:len(self.__tags)])
        self.__write("<!-- %s -->\n" % escape_comment(comment))

    def data(self, text):
        """
        Adds character data to the output stream.

        Parameters
        ----------
        text : str
            Character data.
        """
        self.__data.append(text)

    def end(self, tag=None, indent=True):
        """
        Closes the current element (opened by the most recent call to
        :meth:`start`).

        Parameters
        ----------
        tag
            Element tag.  If given, the tag must match the start tag.  If
            omitted, the current element is closed.
       """
        if tag:
            assert self.__tags, "unbalanced end(%s)" % tag
            assert escape_cdata(tag) == self.__tags[-1], \
                "expected end(%s), got %s" % (self.__tags[-1], tag)
        else:
            assert self.__tags, "unbalanced end()"
        tag = self.__tags.pop()
        if self.__data:
            self.__flush(indent)
        elif self.__open:
            self.__open = 0
            self.__write("/>\n")
            return
        if indent:
            self.__write(self.__indentation[:len(self.__tags)])
        self.__write("</%s>\n" % tag)

    def close(self, id):
        """
        Closes open elements, up to (and including) the element identified
        by the given identifier.

        Parameters
        ----------
        id
            Element identifier, as returned by the :meth:`start` method.
        """
        while len(self.__tags) > id:
            self.end()

    def element(self, tag, text=None, attrib={}, **extra):
        """
        Adds an entire element.  This is the same as calling :meth:`start`,
        :meth:`data`, and :meth:`end` in sequence. The *text* argument can be
        omitted.
        """
        self.start(tag, attrib, **extra)
        if text:
            self.data(text)
        self.end(indent=False)

    def flush(self):
        """Flushes the output stream."""
        pass  # replaced by the constructor


def generate_transform(transform_list=[]):
    if len(transform_list):
        output = io.StringIO()
        for type, value in transform_list:
            if (type == 'scale' and (value == (1,) or value == (1, 1))
                    or type == 'translate' and value == (0, 0)
                    or type == 'rotate' and value == (0,)):
                continue
            if type == 'matrix' and isinstance(value, Affine2DBase):
                value = value.to_values()
            output.write('%s(%s)' % (
                type, ' '.join(short_float_fmt(x) for x in value)))
        return output.getvalue()
    return ''


def generate_css(attrib={}):
    if attrib:
        output = io.StringIO()
        attrib = sorted(attrib.items())
        for k, v in attrib:
            k = escape_attrib(k)
            v = escape_attrib(v)
            output.write("%s:%s;" % (k, v))
        return output.getvalue()
    return ''


_capstyle_d = {'projecting': 'square', 'butt': 'butt', 'round': 'round'}


class RendererSVG(RendererBase):
    def __init__(self, width, height, svgwriter, basename=None, image_dpi=72):
        self.width = width
        self.height = height
        self.writer = XMLWriter(svgwriter)
        self.image_dpi = image_dpi  # actual dpi at which we rasterize stuff

        self._groupd = {}
        self.basename = basename
        self._image_counter = itertools.count()
        self._clipd = OrderedDict()
        self._markers = {}
        self._path_collection_id = 0
        self._hatchd = OrderedDict()
        self._has_gouraud = False
        self._n_gradients = 0
        self._fonts = OrderedDict()
        self.mathtext_parser = MathTextParser('SVG')

        RendererBase.__init__(self)
        self._glyph_map = dict()
        str_height = short_float_fmt(height)
        str_width = short_float_fmt(width)
        svgwriter.write(svgProlog)
        self._start_id = self.writer.start(
            'svg',
            width='%spt' % str_width,
            height='%spt' % str_height,
            viewBox='0 0 %s %s' % (str_width, str_height),
            xmlns="http://www.w3.org/2000/svg",
            version="1.1",
            attrib={'xmlns:xlink': "http://www.w3.org/1999/xlink"})
        self._write_default_style()

    def finalize(self):
        self._write_clips()
        self._write_hatches()
        self.writer.close(self._start_id)
        self.writer.flush()

    def _write_default_style(self):
        writer = self.writer
        default_style = generate_css({
            'stroke-linejoin': 'round',
            'stroke-linecap': 'butt'})
        writer.start('defs')
        writer.start('style', type='text/css')
        writer.data('*{%s}\n' % default_style)
        writer.end('style')
        writer.end('defs')

    def _make_id(self, type, content):
        salt = rcParams['svg.hashsalt']
        if salt is None:
            salt = str(uuid.uuid4())
        m = hashlib.md5()
        m.update(salt.encode('utf8'))
        m.update(str(content).encode('utf8'))
        return '%s%s' % (type, m.hexdigest()[:10])

    def _make_flip_transform(self, transform):
        return (transform +
                Affine2D()
                .scale(1.0, -1.0)
                .translate(0.0, self.height))

    def _get_font(self, prop):
        fname = findfont(prop)
        font = get_font(fname)
        font.clear()
        size = prop.get_size_in_points()
        font.set_size(size, 72.0)
        return font

    def _get_hatch(self, gc, rgbFace):
        """
        Create a new hatch pattern
        """
        if rgbFace is not None:
            rgbFace = tuple(rgbFace)
        edge = gc.get_hatch_color()
        if edge is not None:
            edge = tuple(edge)
        dictkey = (gc.get_hatch(), rgbFace, edge)
        oid = self._hatchd.get(dictkey)
        if oid is None:
            oid = self._make_id('h', dictkey)
            self._hatchd[dictkey] = ((gc.get_hatch_path(), rgbFace, edge), oid)
        else:
            _, oid = oid
        return oid

    def _write_hatches(self):
        if not len(self._hatchd):
            return
        HATCH_SIZE = 72
        writer = self.writer
        writer.start('defs')
        for (path, face, stroke), oid in self._hatchd.values():
            writer.start(
                'pattern',
                id=oid,
                patternUnits="userSpaceOnUse",
                x="0", y="0", width=str(HATCH_SIZE),
                height=str(HATCH_SIZE))
            path_data = self._convert_path(
                path,
                Affine2D()
                .scale(HATCH_SIZE).scale(1.0, -1.0).translate(0, HATCH_SIZE),
                simplify=False)
            if face is None:
                fill = 'none'
            else:
                fill = rgb2hex(face)
            writer.element(
                'rect',
                x="0", y="0", width=str(HATCH_SIZE+1),
                height=str(HATCH_SIZE+1),
                fill=fill)
            writer.element(
                'path',
                d=path_data,
                style=generate_css({
                    'fill': rgb2hex(stroke),
                    'stroke': rgb2hex(stroke),
                    'stroke-width': str(rcParams['hatch.linewidth']),
                    'stroke-linecap': 'butt',
                    'stroke-linejoin': 'miter'
                    })
                )
            writer.end('pattern')
        writer.end('defs')

    def _get_style_dict(self, gc, rgbFace):
        """Generate a style string from the GraphicsContext and rgbFace."""
        attrib = {}

        forced_alpha = gc.get_forced_alpha()

        if gc.get_hatch() is not None:
            attrib['fill'] = "url(#%s)" % self._get_hatch(gc, rgbFace)
            if (rgbFace is not None and len(rgbFace) == 4 and rgbFace[3] != 1.0
                    and not forced_alpha):
                attrib['fill-opacity'] = short_float_fmt(rgbFace[3])
        else:
            if rgbFace is None:
                attrib['fill'] = 'none'
            else:
                if tuple(rgbFace[:3]) != (0, 0, 0):
                    attrib['fill'] = rgb2hex(rgbFace)
                if (len(rgbFace) == 4 and rgbFace[3] != 1.0
                        and not forced_alpha):
                    attrib['fill-opacity'] = short_float_fmt(rgbFace[3])

        if forced_alpha and gc.get_alpha() != 1.0:
            attrib['opacity'] = short_float_fmt(gc.get_alpha())

        offset, seq = gc.get_dashes()
        if seq is not None:
            attrib['stroke-dasharray'] = ','.join(
                short_float_fmt(val) for val in seq)
            attrib['stroke-dashoffset'] = short_float_fmt(float(offset))

        linewidth = gc.get_linewidth()
        if linewidth:
            rgb = gc.get_rgb()
            attrib['stroke'] = rgb2hex(rgb)
            if not forced_alpha and rgb[3] != 1.0:
                attrib['stroke-opacity'] = short_float_fmt(rgb[3])
            if linewidth != 1.0:
                attrib['stroke-width'] = short_float_fmt(linewidth)
            if gc.get_joinstyle() != 'round':
                attrib['stroke-linejoin'] = gc.get_joinstyle()
            if gc.get_capstyle() != 'butt':
                attrib['stroke-linecap'] = _capstyle_d[gc.get_capstyle()]

        return attrib

    def _get_style(self, gc, rgbFace):
        return generate_css(self._get_style_dict(gc, rgbFace))

    def _get_clip(self, gc):
        cliprect = gc.get_clip_rectangle()
        clippath, clippath_trans = gc.get_clip_path()
        if clippath is not None:
            clippath_trans = self._make_flip_transform(clippath_trans)
            dictkey = (id(clippath), str(clippath_trans))
        elif cliprect is not None:
            x, y, w, h = cliprect.bounds
            y = self.height-(y+h)
            dictkey = (x, y, w, h)
        else:
            return None

        clip = self._clipd.get(dictkey)
        if clip is None:
            oid = self._make_id('p', dictkey)
            if clippath is not None:
                self._clipd[dictkey] = ((clippath, clippath_trans), oid)
            else:
                self._clipd[dictkey] = (dictkey, oid)
        else:
            clip, oid = clip
        return oid

    def _write_clips(self):
        if not len(self._clipd):
            return
        writer = self.writer
        writer.start('defs')
        for clip, oid in self._clipd.values():
            writer.start('clipPath', id=oid)
            if len(clip) == 2:
                clippath, clippath_trans = clip
                path_data = self._convert_path(
                    clippath, clippath_trans, simplify=False)
                writer.element('path', d=path_data)
            else:
                x, y, w, h = clip
                writer.element(
                    'rect',
                    x=short_float_fmt(x),
                    y=short_float_fmt(y),
                    width=short_float_fmt(w),
                    height=short_float_fmt(h))
            writer.end('clipPath')
        writer.end('defs')

    def open_group(self, s, gid=None):
        # docstring inherited
        if gid:
            self.writer.start('g', id=gid)
        else:
            self._groupd[s] = self._groupd.get(s, 0) + 1
            self.writer.start('g', id="%s_%d" % (s, self._groupd[s]))

    def close_group(self, s):
        # docstring inherited
        self.writer.end('g')

    def option_image_nocomposite(self):
        # docstring inherited
        return not rcParams['image.composite_image']

    def _convert_path(self, path, transform=None, clip=None, simplify=None,
                      sketch=None):
        if clip:
            clip = (0.0, 0.0, self.width, self.height)
        else:
            clip = None
        return _path.convert_to_string(
            path, transform, clip, simplify, sketch, 6,
            [b'M', b'L', b'Q', b'C', b'z'], False).decode('ascii')

    def draw_path(self, gc, path, transform, rgbFace=None):
        # docstring inherited
        trans_and_flip = self._make_flip_transform(transform)
        clip = (rgbFace is None and gc.get_hatch_path() is None)
        simplify = path.should_simplify and clip
        path_data = self._convert_path(
            path, trans_and_flip, clip=clip, simplify=simplify,
            sketch=gc.get_sketch_params())

        attrib = {}
        attrib['style'] = self._get_style(gc, rgbFace)

        clipid = self._get_clip(gc)
        if clipid is not None:
            attrib['clip-path'] = 'url(#%s)' % clipid

        if gc.get_url() is not None:
            self.writer.start('a', {'xlink:href': gc.get_url()})
        self.writer.element('path', d=path_data, attrib=attrib)
        if gc.get_url() is not None:
            self.writer.end('a')

    def draw_markers(
            self, gc, marker_path, marker_trans, path, trans, rgbFace=None):
        # docstring inherited

        if not len(path.vertices):
            return

        writer = self.writer
        path_data = self._convert_path(
            marker_path,
            marker_trans + Affine2D().scale(1.0, -1.0),
            simplify=False)
        style = self._get_style_dict(gc, rgbFace)
        dictkey = (path_data, generate_css(style))
        oid = self._markers.get(dictkey)
        style = generate_css({k: v for k, v in style.items()
                              if k.startswith('stroke')})

        if oid is None:
            oid = self._make_id('m', dictkey)
            writer.start('defs')
            writer.element('path', id=oid, d=path_data, style=style)
            writer.end('defs')
            self._markers[dictkey] = oid

        attrib = {}
        clipid = self._get_clip(gc)
        if clipid is not None:
            attrib['clip-path'] = 'url(#%s)' % clipid
        writer.start('g', attrib=attrib)

        trans_and_flip = self._make_flip_transform(trans)
        attrib = {'xlink:href': '#%s' % oid}
        clip = (0, 0, self.width*72, self.height*72)
        for vertices, code in path.iter_segments(
                trans_and_flip, clip=clip, simplify=False):
            if len(vertices):
                x, y = vertices[-2:]
                attrib['x'] = short_float_fmt(x)
                attrib['y'] = short_float_fmt(y)
                attrib['style'] = self._get_style(gc, rgbFace)
                writer.element('use', attrib=attrib)
        writer.end('g')

    def draw_path_collection(self, gc, master_transform, paths, all_transforms,
                             offsets, offsetTrans, facecolors, edgecolors,
                             linewidths, linestyles, antialiaseds, urls,
                             offset_position):
        # Is the optimization worth it? Rough calculation:
        # cost of emitting a path in-line is
        #    (len_path + 5) * uses_per_path
        # cost of definition+use is
        #    (len_path + 3) + 9 * uses_per_path
        len_path = len(paths[0].vertices) if len(paths) > 0 else 0
        uses_per_path = self._iter_collection_uses_per_path(
            paths, all_transforms, offsets, facecolors, edgecolors)
        should_do_optimization = \
            len_path + 9 * uses_per_path + 3 < (len_path + 5) * uses_per_path
        if not should_do_optimization:
            return RendererBase.draw_path_collection(
                self, gc, master_transform, paths, all_transforms,
                offsets, offsetTrans, facecolors, edgecolors,
                linewidths, linestyles, antialiaseds, urls,
                offset_position)

        writer = self.writer
        path_codes = []
        writer.start('defs')
        for i, (path, transform) in enumerate(self._iter_collection_raw_paths(
                master_transform, paths, all_transforms)):
            transform = Affine2D(transform.get_matrix()).scale(1.0, -1.0)
            d = self._convert_path(path, transform, simplify=False)
            oid = 'C%x_%x_%s' % (
                self._path_collection_id, i, self._make_id('', d))
            writer.element('path', id=oid, d=d)
            path_codes.append(oid)
        writer.end('defs')

        for xo, yo, path_id, gc0, rgbFace in self._iter_collection(
                gc, master_transform, all_transforms, path_codes, offsets,
                offsetTrans, facecolors, edgecolors, linewidths, linestyles,
                antialiaseds, urls, offset_position):
            clipid = self._get_clip(gc0)
            url = gc0.get_url()
            if url is not None:
                writer.start('a', attrib={'xlink:href': url})
            if clipid is not None:
                writer.start('g', attrib={'clip-path': 'url(#%s)' % clipid})
            attrib = {
                'xlink:href': '#%s' % path_id,
                'x': short_float_fmt(xo),
                'y': short_float_fmt(self.height - yo),
                'style': self._get_style(gc0, rgbFace)
                }
            writer.element('use', attrib=attrib)
            if clipid is not None:
                writer.end('g')
            if url is not None:
                writer.end('a')

        self._path_collection_id += 1

    def draw_gouraud_triangle(self, gc, points, colors, trans):
        # This uses a method described here:
        #
        #   http://www.svgopen.org/2005/papers/Converting3DFaceToSVG/index.html
        #
        # that uses three overlapping linear gradients to simulate a
        # Gouraud triangle.  Each gradient goes from fully opaque in
        # one corner to fully transparent along the opposite edge.
        # The line between the stop points is perpendicular to the
        # opposite edge.  Underlying these three gradients is a solid
        # triangle whose color is the average of all three points.

        writer = self.writer
        if not self._has_gouraud:
            self._has_gouraud = True
            writer.start(
                'filter',
                id='colorAdd')
            writer.element(
                'feComposite',
                attrib={'in': 'SourceGraphic'},
                in2='BackgroundImage',
                operator='arithmetic',
                k2="1", k3="1")
            writer.end('filter')
            # feColorMatrix filter to correct opacity
            writer.start(
                'filter',
                id='colorMat')
            writer.element(
                'feColorMatrix',
                attrib={'type': 'matrix'},
                values='1 0 0 0 0 \n0 1 0 0 0 \n0 0 1 0 0' +
                       ' \n1 1 1 1 0 \n0 0 0 0 1 ')
            writer.end('filter')

        avg_color = np.sum(colors[:, :], axis=0) / 3.0
        # Just skip fully-transparent triangles
        if avg_color[-1] == 0.0:
            return

        trans_and_flip = self._make_flip_transform(trans)
        tpoints = trans_and_flip.transform(points)

        writer.start('defs')
        for i in range(3):
            x1, y1 = tpoints[i]
            x2, y2 = tpoints[(i + 1) % 3]
            x3, y3 = tpoints[(i + 2) % 3]
            c = colors[i][:]

            if x2 == x3:
                xb = x2
                yb = y1
            elif y2 == y3:
                xb = x1
                yb = y2
            else:
                m1 = (y2 - y3) / (x2 - x3)
                b1 = y2 - (m1 * x2)
                m2 = -(1.0 / m1)
                b2 = y1 - (m2 * x1)
                xb = (-b1 + b2) / (m1 - m2)
                yb = m2 * xb + b2

            writer.start(
                'linearGradient',
                id="GR%x_%d" % (self._n_gradients, i),
                gradientUnits="userSpaceOnUse",
                x1=short_float_fmt(x1), y1=short_float_fmt(y1),
                x2=short_float_fmt(xb), y2=short_float_fmt(yb))
            writer.element(
                'stop',
                offset='1',
                style=generate_css({'stop-color': rgb2hex(avg_color),
                                    'stop-opacity': short_float_fmt(c[-1])}))
            writer.element(
                'stop',
                offset='0',
                style=generate_css({'stop-color': rgb2hex(c),
                                    'stop-opacity': "0"}))

            writer.end('linearGradient')

        writer.end('defs')

        # triangle formation using "path"
        dpath = "M " + short_float_fmt(x1)+',' + short_float_fmt(y1)
        dpath += " L " + short_float_fmt(x2) + ',' + short_float_fmt(y2)
        dpath += " " + short_float_fmt(x3) + ',' + short_float_fmt(y3) + " Z"

        writer.element(
            'path',
            attrib={'d': dpath,
                    'fill': rgb2hex(avg_color),
                    'fill-opacity': '1',
                    'shape-rendering': "crispEdges"})

        writer.start(
                'g',
                attrib={'stroke': "none",
                        'stroke-width': "0",
                        'shape-rendering': "crispEdges",
                        'filter': "url(#colorMat)"})

        writer.element(
            'path',
            attrib={'d': dpath,
                    'fill': 'url(#GR%x_0)' % self._n_gradients,
                    'shape-rendering': "crispEdges"})

        writer.element(
            'path',
            attrib={'d': dpath,
                    'fill': 'url(#GR%x_1)' % self._n_gradients,
                    'filter': 'url(#colorAdd)',
                    'shape-rendering': "crispEdges"})

        writer.element(
            'path',
            attrib={'d': dpath,
                    'fill': 'url(#GR%x_2)' % self._n_gradients,
                    'filter': 'url(#colorAdd)',
                    'shape-rendering': "crispEdges"})

        writer.end('g')

        self._n_gradients += 1

    def draw_gouraud_triangles(self, gc, triangles_array, colors_array,
                               transform):
        attrib = {}
        clipid = self._get_clip(gc)
        if clipid is not None:
            attrib['clip-path'] = 'url(#%s)' % clipid

        self.writer.start('g', attrib=attrib)

        transform = transform.frozen()
        for tri, col in zip(triangles_array, colors_array):
            self.draw_gouraud_triangle(gc, tri, col, transform)

        self.writer.end('g')

    def option_scale_image(self):
        # docstring inherited
        return True

    def get_image_magnification(self):
        return self.image_dpi / 72.0

    def draw_image(self, gc, x, y, im, transform=None):
        # docstring inherited

        h, w = im.shape[:2]

        if w == 0 or h == 0:
            return

        attrib = {}
        clipid = self._get_clip(gc)
        if clipid is not None:
            # Can't apply clip-path directly to the image because the
            # image has a transformation, which would also be applied
            # to the clip-path
            self.writer.start('g', attrib={'clip-path': 'url(#%s)' % clipid})

        oid = gc.get_gid()
        url = gc.get_url()
        if url is not None:
            self.writer.start('a', attrib={'xlink:href': url})
        if rcParams['svg.image_inline']:
            buf = _png.write_png(im, None)
            oid = oid or self._make_id('image', buf)
            attrib['xlink:href'] = (
                "data:image/png;base64,\n" +
                base64.b64encode(buf).decode('ascii'))
        else:
            if self.basename is None:
                raise ValueError("Cannot save image data to filesystem when "
                                 "writing SVG to an in-memory buffer")
            filename = '{}.image{}.png'.format(
                self.basename, next(self._image_counter))
            _log.info('Writing image file for inclusion: %s', filename)
            with open(filename, 'wb') as file:
                _png.write_png(im, file)
            oid = oid or 'Im_' + self._make_id('image', filename)
            attrib['xlink:href'] = filename

        attrib['id'] = oid

        if transform is None:
            w = 72.0 * w / self.image_dpi
            h = 72.0 * h / self.image_dpi

            self.writer.element(
                'image',
                transform=generate_transform([
                    ('scale', (1, -1)), ('translate', (0, -h))]),
                x=short_float_fmt(x),
                y=short_float_fmt(-(self.height - y - h)),
                width=short_float_fmt(w), height=short_float_fmt(h),
                attrib=attrib)
        else:
            alpha = gc.get_alpha()
            if alpha != 1.0:
                attrib['opacity'] = short_float_fmt(alpha)

            flipped = (
                Affine2D().scale(1.0 / w, 1.0 / h) +
                transform +
                Affine2D()
                .translate(x, y)
                .scale(1.0, -1.0)
                .translate(0.0, self.height))

            attrib['transform'] = generate_transform(
                [('matrix', flipped.frozen())])
            self.writer.element(
                'image',
                width=short_float_fmt(w), height=short_float_fmt(h),
                attrib=attrib)

        if url is not None:
            self.writer.end('a')
        if clipid is not None:
            self.writer.end('g')

    def _adjust_char_id(self, char_id):
        return char_id.replace("%20", "_")

    def _draw_text_as_path(self, gc, x, y, s, prop, angle, ismath, mtext=None):
        """
        draw the text by converting them to paths using textpath module.

        Parameters
        ----------
        prop : `matplotlib.font_manager.FontProperties`
          font property

        s : str
          text to be converted

        usetex : bool
          If True, use matplotlib usetex mode.

        ismath : bool
          If True, use mathtext parser. If "TeX", use *usetex* mode.

        """
        writer = self.writer

        writer.comment(s)

        glyph_map = self._glyph_map

        text2path = self._text2path
        color = rgb2hex(gc.get_rgb())
        fontsize = prop.get_size_in_points()

        style = {}
        if color != '#000000':
            style['fill'] = color

        alpha = gc.get_alpha() if gc.get_forced_alpha() else gc.get_rgb()[3]
        if alpha != 1:
            style['opacity'] = short_float_fmt(alpha)

        if not ismath:
            font = text2path._get_font(prop)
            _glyphs = text2path.get_glyphs_with_font(
                font, s, glyph_map=glyph_map, return_new_glyphs_only=True)
            glyph_info, glyph_map_new, rects = _glyphs

            if glyph_map_new:
                writer.start('defs')
                for char_id, glyph_path in glyph_map_new.items():
                    path = Path(*glyph_path)
                    path_data = self._convert_path(path, simplify=False)
                    writer.element('path', id=char_id, d=path_data)
                writer.end('defs')

                glyph_map.update(glyph_map_new)

            attrib = {}
            attrib['style'] = generate_css(style)
            font_scale = fontsize / text2path.FONT_SCALE
            attrib['transform'] = generate_transform([
                ('translate', (x, y)),
                ('rotate', (-angle,)),
                ('scale', (font_scale, -font_scale))])

            writer.start('g', attrib=attrib)
            for glyph_id, xposition, yposition, scale in glyph_info:
                attrib = {'xlink:href': '#%s' % glyph_id}
                if xposition != 0.0:
                    attrib['x'] = short_float_fmt(xposition)
                if yposition != 0.0:
                    attrib['y'] = short_float_fmt(yposition)
                writer.element(
                    'use',
                    attrib=attrib)

            writer.end('g')
        else:
            if ismath == "TeX":
                _glyphs = text2path.get_glyphs_tex(
                    prop, s, glyph_map=glyph_map, return_new_glyphs_only=True)
            else:
                _glyphs = text2path.get_glyphs_mathtext(
                    prop, s, glyph_map=glyph_map, return_new_glyphs_only=True)

            glyph_info, glyph_map_new, rects = _glyphs

            # We store the character glyphs w/o flipping.  Instead, the
            # coordinate will be flipped when these characters are used.
            if glyph_map_new:
                writer.start('defs')
                for char_id, glyph_path in glyph_map_new.items():
                    char_id = self._adjust_char_id(char_id)
                    # Some characters are blank
                    if not len(glyph_path[0]):
                        path_data = ""
                    else:
                        path = Path(*glyph_path)
                        path_data = self._convert_path(path, simplify=False)
                    writer.element('path', id=char_id, d=path_data)
                writer.end('defs')

                glyph_map.update(glyph_map_new)

            attrib = {}
            font_scale = fontsize / text2path.FONT_SCALE
            attrib['style'] = generate_css(style)
            attrib['transform'] = generate_transform([
                ('translate', (x, y)),
                ('rotate', (-angle,)),
                ('scale', (font_scale, -font_scale))])

            writer.start('g', attrib=attrib)
            for char_id, xposition, yposition, scale in glyph_info:
                char_id = self._adjust_char_id(char_id)

                writer.element(
                    'use',
                    transform=generate_transform([
                        ('translate', (xposition, yposition)),
                        ('scale', (scale,)),
                        ]),
                    attrib={'xlink:href': '#%s' % char_id})

            for verts, codes in rects:
                path = Path(verts, codes)
                path_data = self._convert_path(path, simplify=False)
                writer.element('path', d=path_data)

            writer.end('g')

    def _draw_text_as_text(self, gc, x, y, s, prop, angle, ismath, mtext=None):
        writer = self.writer

        color = rgb2hex(gc.get_rgb())
        style = {}
        if color != '#000000':
            style['fill'] = color

        alpha = gc.get_alpha() if gc.get_forced_alpha() else gc.get_rgb()[3]
        if alpha != 1:
            style['opacity'] = short_float_fmt(alpha)

        if not ismath:
            font = self._get_font(prop)
            font.set_text(s, 0.0, flags=LOAD_NO_HINTING)

            attrib = {}
            # Must add "px" to workaround a Firefox bug
            style['font-size'] = short_float_fmt(prop.get_size()) + 'px'
            style['font-family'] = str(font.family_name)
            style['font-style'] = prop.get_style().lower()
            style['font-weight'] = str(prop.get_weight()).lower()
            attrib['style'] = generate_css(style)

            if mtext and (angle == 0 or mtext.get_rotation_mode() == "anchor"):
                # If text anchoring can be supported, get the original
                # coordinates and add alignment information.

                # Get anchor coordinates.
                transform = mtext.get_transform()
                ax, ay = transform.transform(mtext.get_unitless_position())
                ay = self.height - ay

                # Don't do vertical anchor alignment. Most applications do not
                # support 'alignment-baseline' yet. Apply the vertical layout
                # to the anchor point manually for now.
                angle_rad = np.deg2rad(angle)
                dir_vert = np.array([np.sin(angle_rad), np.cos(angle_rad)])
                v_offset = np.dot(dir_vert, [(x - ax), (y - ay)])
                ax = ax + v_offset * dir_vert[0]
                ay = ay + v_offset * dir_vert[1]

                ha_mpl_to_svg = {'left': 'start', 'right': 'end',
                                 'center': 'middle'}
                style['text-anchor'] = ha_mpl_to_svg[mtext.get_ha()]

                attrib['x'] = short_float_fmt(ax)
                attrib['y'] = short_float_fmt(ay)
                attrib['style'] = generate_css(style)
                attrib['transform'] = "rotate(%s, %s, %s)" % (
                    short_float_fmt(-angle),
                    short_float_fmt(ax),
                    short_float_fmt(ay))
                writer.element('text', s, attrib=attrib)
            else:
                attrib['transform'] = generate_transform([
                    ('translate', (x, y)),
                    ('rotate', (-angle,))])

                writer.element('text', s, attrib=attrib)

        else:
            writer.comment(s)

            width, height, descent, svg_elements, used_characters = \
                self.mathtext_parser.parse(s, 72, prop)
            svg_glyphs = svg_elements.svg_glyphs
            svg_rects = svg_elements.svg_rects

            attrib = {}
            attrib['style'] = generate_css(style)
            attrib['transform'] = generate_transform([
                ('translate', (x, y)),
                ('rotate', (-angle,))])

            # Apply attributes to 'g', not 'text', because we likely have some
            # rectangles as well with the same style and transformation.
            writer.start('g', attrib=attrib)

            writer.start('text')

            # Sort the characters by font, and output one tspan for each.
            spans = OrderedDict()
            for font, fontsize, thetext, new_x, new_y, metrics in svg_glyphs:
                style = generate_css({
                    'font-size': short_float_fmt(fontsize) + 'px',
                    'font-family': font.family_name,
                    'font-style': font.style_name.lower(),
                    'font-weight': font.style_name.lower()})
                if thetext == 32:
                    thetext = 0xa0  # non-breaking space
                spans.setdefault(style, []).append((new_x, -new_y, thetext))

            for style, chars in spans.items():
                chars.sort()

                if len({y for x, y, t in chars}) == 1:  # Are all y's the same?
                    ys = str(chars[0][1])
                else:
                    ys = ' '.join(str(c[1]) for c in chars)

                attrib = {
                    'style': style,
                    'x': ' '.join(short_float_fmt(c[0]) for c in chars),
                    'y': ys
                    }

                writer.element(
                    'tspan',
                    ''.join(chr(c[2]) for c in chars),
                    attrib=attrib)

            writer.end('text')

            if len(svg_rects):
                for x, y, width, height in svg_rects:
                    writer.element(
                        'rect',
                        x=short_float_fmt(x),
                        y=short_float_fmt(-y + height),
                        width=short_float_fmt(width),
                        height=short_float_fmt(height)
                        )

            writer.end('g')

    def draw_tex(self, gc, x, y, s, prop, angle, ismath='TeX!', mtext=None):
        # docstring inherited
        self._draw_text_as_path(gc, x, y, s, prop, angle, ismath="TeX")

    def draw_text(self, gc, x, y, s, prop, angle, ismath=False, mtext=None):
        # docstring inherited

        clipid = self._get_clip(gc)
        if clipid is not None:
            # Cannot apply clip-path directly to the text, because
            # is has a transformation
            self.writer.start(
                'g', attrib={'clip-path': 'url(#%s)' % clipid})

        if gc.get_url() is not None:
            self.writer.start('a', {'xlink:href': gc.get_url()})

        if rcParams['svg.fonttype'] == 'path':
            self._draw_text_as_path(gc, x, y, s, prop, angle, ismath, mtext)
        else:
            self._draw_text_as_text(gc, x, y, s, prop, angle, ismath, mtext)

        if gc.get_url() is not None:
            self.writer.end('a')

        if clipid is not None:
            self.writer.end('g')

    def flipy(self):
        # docstring inherited
        return True

    def get_canvas_width_height(self):
        # docstring inherited
        return self.width, self.height

    def get_text_width_height_descent(self, s, prop, ismath):
        # docstring inherited
        return self._text2path.get_text_width_height_descent(s, prop, ismath)


class FigureCanvasSVG(FigureCanvasBase):
    filetypes = {'svg': 'Scalable Vector Graphics',
                 'svgz': 'Scalable Vector Graphics'}

    fixed_dpi = 72

    def print_svg(self, filename, *args, **kwargs):
        with cbook.open_file_cm(filename, "w", encoding="utf-8") as fh:

            filename = getattr(fh, 'name', '')
            if not isinstance(filename, str):
                filename = ''

            if cbook.file_requires_unicode(fh):
                detach = False
            else:
                fh = io.TextIOWrapper(fh, 'utf-8')
                detach = True

            result = self._print_svg(filename, fh, **kwargs)

            # Detach underlying stream from wrapper so that it remains open in
            # the caller.
            if detach:
                fh.detach()

        return result

    def print_svgz(self, filename, *args, **kwargs):
        with cbook.open_file_cm(filename, "wb") as fh, \
                gzip.GzipFile(mode='w', fileobj=fh) as gzipwriter:
            return self.print_svg(gzipwriter)

    def _print_svg(
            self, filename, fh, *, dpi=72, bbox_inches_restore=None, **kwargs):
        self.figure.set_dpi(72.0)
        width, height = self.figure.get_size_inches()
        w, h = width * 72, height * 72

        renderer = MixedModeRenderer(
            self.figure, width, height, dpi,
            RendererSVG(w, h, fh, filename, dpi),
            bbox_inches_restore=bbox_inches_restore)

        self.figure.draw(renderer)
        renderer.finalize()

    def get_default_filetype(self):
        return 'svg'


FigureManagerSVG = FigureManagerBase


svgProlog = """\
<?xml version="1.0" encoding="utf-8" standalone="no"?>
<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN"
  "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">
<!-- Created with matplotlib (https://matplotlib.org/) -->
"""


@_Backend.export
class _BackendSVG(_Backend):
    FigureCanvas = FigureCanvasSVG