latextools.py

# -*- coding: utf-8 -*-
"""Tools for handling LaTeX."""

# Copyright (c) IPython Development Team.
# Distributed under the terms of the Modified BSD License.

from io import BytesIO, open
import os
import tempfile
import shutil
import subprocess
from base64 import encodebytes
import textwrap

from pathlib import Path

from IPython.utils.process import find_cmd, FindCmdError
from traitlets.config import get_config
from traitlets.config.configurable import SingletonConfigurable
from traitlets import List, Bool, Unicode
from IPython.utils.py3compat import cast_unicode


class LaTeXTool(SingletonConfigurable):
    """An object to store configuration of the LaTeX tool."""
    def _config_default(self):
        return get_config()

    backends = List(
        Unicode(), ["matplotlib", "dvipng"],
        help="Preferred backend to draw LaTeX math equations. "
        "Backends in the list are checked one by one and the first "
        "usable one is used.  Note that `matplotlib` backend "
        "is usable only for inline style equations.  To draw  "
        "display style equations, `dvipng` backend must be specified. ",
        # It is a List instead of Enum, to make configuration more
        # flexible.  For example, to use matplotlib mainly but dvipng
        # for display style, the default ["matplotlib", "dvipng"] can
        # be used.  To NOT use dvipng so that other repr such as
        # unicode pretty printing is used, you can use ["matplotlib"].
        ).tag(config=True)

    use_breqn = Bool(
        True,
        help="Use breqn.sty to automatically break long equations. "
        "This configuration takes effect only for dvipng backend.",
        ).tag(config=True)

    packages = List(
        ['amsmath', 'amsthm', 'amssymb', 'bm'],
        help="A list of packages to use for dvipng backend. "
        "'breqn' will be automatically appended when use_breqn=True.",
        ).tag(config=True)

    preamble = Unicode(
        help="Additional preamble to use when generating LaTeX source "
        "for dvipng backend.",
        ).tag(config=True)


def latex_to_png(s, encode=False, backend=None, wrap=False, color='Black',
                 scale=1.0):
    """Render a LaTeX string to PNG.

    Parameters
    ----------
    s : str
        The raw string containing valid inline LaTeX.
    encode : bool, optional
        Should the PNG data base64 encoded to make it JSON'able.
    backend : {matplotlib, dvipng}
        Backend for producing PNG data.
    wrap : bool
        If true, Automatically wrap `s` as a LaTeX equation.
    color : string
        Foreground color name among dvipsnames, e.g. 'Maroon' or on hex RGB
        format, e.g. '#AA20FA'.
    scale : float
        Scale factor for the resulting PNG.
    None is returned when the backend cannot be used.

    """
    s = cast_unicode(s)
    allowed_backends = LaTeXTool.instance().backends
    if backend is None:
        backend = allowed_backends[0]
    if backend not in allowed_backends:
        return None
    if backend == 'matplotlib':
        f = latex_to_png_mpl
    elif backend == 'dvipng':
        f = latex_to_png_dvipng
        if color.startswith('#'):
            # Convert hex RGB color to LaTeX RGB color.
            if len(color) == 7:
                try:
                    color = "RGB {}".format(" ".join([str(int(x, 16)) for x in
                                                      textwrap.wrap(color[1:], 2)]))
                except ValueError as e:
                    raise ValueError('Invalid color specification {}.'.format(color)) from e
            else:
                raise ValueError('Invalid color specification {}.'.format(color))
    else:
        raise ValueError('No such backend {0}'.format(backend))
    bin_data = f(s, wrap, color, scale)
    if encode and bin_data:
        bin_data = encodebytes(bin_data)
    return bin_data


def latex_to_png_mpl(s, wrap, color='Black', scale=1.0):
    try:
        from matplotlib import figure, font_manager, mathtext
        from matplotlib.backends import backend_agg
        from pyparsing import ParseFatalException
    except ImportError:
        return None

    # mpl mathtext doesn't support display math, force inline
    s = s.replace('$$', '$')
    if wrap:
        s = u'${0}$'.format(s)

    try:
        prop = font_manager.FontProperties(size=12)
        dpi = 120 * scale
        buffer = BytesIO()

        # Adapted from mathtext.math_to_image
        parser = mathtext.MathTextParser("path")
        width, height, depth, _, _ = parser.parse(s, dpi=72, prop=prop)
        fig = figure.Figure(figsize=(width / 72, height / 72))
        fig.text(0, depth / height, s, fontproperties=prop, color=color)
        backend_agg.FigureCanvasAgg(fig)
        fig.savefig(buffer, dpi=dpi, format="png", transparent=True)
        return buffer.getvalue()
    except (ValueError, RuntimeError, ParseFatalException):
        return None


def latex_to_png_dvipng(s, wrap, color='Black', scale=1.0):
    try:
        find_cmd('latex')
        find_cmd('dvipng')
    except FindCmdError:
        return None

    startupinfo = None
    if os.name == "nt":
        # prevent popup-windows
        startupinfo = subprocess.STARTUPINFO()
        startupinfo.dwFlags |= subprocess.STARTF_USESHOWWINDOW

    try:
        workdir = Path(tempfile.mkdtemp())
        tmpfile = "tmp.tex"
        dvifile = "tmp.dvi"
        outfile = "tmp.png"

        with workdir.joinpath(tmpfile).open("w", encoding="utf8") as f:
            f.writelines(genelatex(s, wrap))

        subprocess.check_call(
            ["latex", "-halt-on-error", "-interaction", "batchmode", tmpfile],
            cwd=workdir,
            stdout=subprocess.DEVNULL,
            stderr=subprocess.DEVNULL,
            startupinfo=startupinfo,
        )

        resolution = round(150 * scale)
        subprocess.check_call(
            [
                "dvipng",
                "-T",
                "tight",
                "-D",
                str(resolution),
                "-z",
                "9",
                "-bg",
                "Transparent",
                "-o",
                outfile,
                dvifile,
                "-fg",
                color,
            ],
            cwd=workdir,
            stdout=subprocess.DEVNULL,
            stderr=subprocess.DEVNULL,
            startupinfo=startupinfo,
        )

        with workdir.joinpath(outfile).open("rb") as f:
            return f.read()
    except subprocess.CalledProcessError:
        return None
    finally:
        shutil.rmtree(workdir)


def kpsewhich(filename):
    """Invoke kpsewhich command with an argument `filename`."""
    try:
        find_cmd("kpsewhich")
        proc = subprocess.Popen(
            ["kpsewhich", filename],
            stdout=subprocess.PIPE, stderr=subprocess.PIPE)
        (stdout, stderr) = proc.communicate()
        return stdout.strip().decode('utf8', 'replace')
    except FindCmdError:
        pass


def genelatex(body, wrap):
    """Generate LaTeX document for dvipng backend."""
    lt = LaTeXTool.instance()
    breqn = wrap and lt.use_breqn and kpsewhich("breqn.sty")
    yield r'\documentclass{article}'
    packages = lt.packages
    if breqn:
        packages = packages + ['breqn']
    for pack in packages:
        yield r'\usepackage{{{0}}}'.format(pack)
    yield r'\pagestyle{empty}'
    if lt.preamble:
        yield lt.preamble
    yield r'\begin{document}'
    if breqn:
        yield r'\begin{dmath*}'
        yield body
        yield r'\end{dmath*}'
    elif wrap:
        yield u'$${0}$$'.format(body)
    else:
        yield body
    yield u'\\end{document}'


_data_uri_template_png = u"""<img src="data:image/png;base64,%s" alt=%s />"""

def latex_to_html(s, alt='image'):
    """Render LaTeX to HTML with embedded PNG data using data URIs.

    Parameters
    ----------
    s : str
        The raw string containing valid inline LateX.
    alt : str
        The alt text to use for the HTML.
    """
    base64_data = latex_to_png(s, encode=True).decode('ascii')
    if base64_data:
        return _data_uri_template_png  % (base64_data, alt)