build.py

#!/usr/bin/env python
# Copyright (c) 2013 The Chromium OS Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.
"""Script to generate bitmaps for firmware screens."""

import argparse
from collections import defaultdict, namedtuple, Counter
import copy
import fractions
import glob
import json
from concurrent.futures import ProcessPoolExecutor
import os
import re
import shutil
import subprocess
import sys

import yaml
from PIL import Image

SCRIPT_BASE = os.path.dirname(os.path.abspath(__file__))

STRINGS_GRD_FILE = 'firmware_strings.grd'
STRINGS_JSON_FILE_TMPL = '{}.json'
FORMAT_FILE = 'format.yaml'
BOARDS_CONFIG_FILE = 'boards.yaml'

OUTPUT_DIR = os.getenv('OUTPUT', os.path.join(SCRIPT_BASE, 'build'))

ONE_LINE_DIR = 'one_line'
SVG_FILES = '*.svg'
PNG_FILES = '*.png'

DIAGNOSTIC_UI = os.getenv('DIAGNOSTIC_UI') == '1'

# String format YAML key names.
KEY_DEFAULT = '_DEFAULT_'
KEY_LOCALES = 'locales'
KEY_GENERIC_FILES = 'generic_files'
KEY_LOCALIZED_FILES = 'localized_files'
KEY_DIAGNOSTIC_FILES = 'diagnostic_files'
KEY_SPRITE_FILES = 'sprite_files'
KEY_STYLES = 'styles'
KEY_BGCOLOR = 'bgcolor'
KEY_FGCOLOR = 'fgcolor'
KEY_HEIGHT = 'height'
KEY_MAX_WIDTH = 'max_width'
KEY_FONTS = 'fonts'

# Board config YAML key names.
KEY_SCREEN = 'screen'
KEY_PANEL = 'panel'
KEY_SDCARD = 'sdcard'
KEY_DPI = 'dpi'
KEY_RTL = 'rtl'
KEY_RW_OVERRIDE = 'rw_override'

BMP_HEADER_OFFSET_NUM_LINES = 6

# Regular expressions used to eliminate spurious spaces and newlines in
# translation strings.
NEWLINE_PATTERN = re.compile(r'([^\n])\n([^\n])')
NEWLINE_REPLACEMENT = r'\1 \2'
CRLF_PATTERN = re.compile(r'\r\n')
MULTIBLANK_PATTERN = re.compile(r'   *')

# The base for bitmap scales, same as UI_SCALE in depthcharge. For example, if
# `SCALE_BASE` is 1000, then height = 200 means 20% of the screen height. Also
# see the 'styles' section in format.yaml.
SCALE_BASE = 1000
DEFAULT_GLYPH_HEIGHT = 20

GLYPH_FONT = 'Cousine'

LocaleInfo = namedtuple('LocaleInfo', ['code', 'rtl'])


class BuildImageError(Exception):
    """Exception for all errors generated during build image process."""


def get_config_with_defaults(configs, key):
    """Gets config of `key` from `configs`.

    If `key` is not present in `configs`, the default config will be returned.
    Similarly, if some config values are missing for `key`, the default ones
    will be used.
    """
    config = configs[KEY_DEFAULT].copy()
    config.update(configs.get(key, {}))
    return config


def load_board_config(filename, board):
    """Loads the configuration of `board` from `filename`.

    Args:
        filename: File name of a YAML config file.
        board: Board name.

    Returns:
        A dictionary mapping each board name to its config.
    """
    with open(filename, 'rb') as file:
        raw = yaml.load(file)

    config = copy.deepcopy(raw[KEY_DEFAULT])
    for boards, params in raw.items():
        if boards == KEY_DEFAULT:
            continue
        if board not in boards.split(','):
            continue
        if params:
            config.update(params)
        break
    else:
        raise BuildImageError('Board config not found for ' + board)

    return config


def check_fonts(fonts):
    """Checks if all fonts are available."""
    for locale, font in fonts.items():
        if subprocess.run(['fc-list', '-q', font],
                          check=False).returncode != 0:
            raise BuildImageError('Font %r not found for locale %r' %
                                  (font, locale))


def run_pango_view(input_file,
                   output_file,
                   locale,
                   font,
                   height,
                   max_width,
                   dpi,
                   bgcolor,
                   fgcolor,
                   hinting='full'):
    """Runs pango-view."""
    command = ['pango-view', '-q']
    if locale:
        command += ['--language', locale]

    # Font size should be proportional to the height. Here we use 2 as the
    # divisor so that setting dpi to 96 (pango-view's default) in boards.yaml
    # will be roughly equivalent to setting the screen resolution to 1366x768.
    font_size = height / 2
    font_spec = '%s %r' % (font, font_size)
    command += ['--font', font_spec]

    if max_width:
        # When converting text to PNG by pango-view, the ratio of image height
        # to the font size is usually no more than 1.1875 (with Roboto).
        # Therefore, set the `max_width_pt` as follows to prevent UI drawing
        # from exceeding the canvas boundary in depthcharge runtime. The divisor
        # 2 is the same in the calculation of `font_size` above.
        max_width_pt = int(max_width / 2 * 1.1875)
        command.append('--width=%d' % max_width_pt)
    if dpi:
        command.append('--dpi=%d' % dpi)
    command.append('--margin=0')
    command += ['--background', bgcolor]
    command += ['--foreground', fgcolor]
    command += ['--hinting', hinting]

    command += ['--output', output_file]
    command.append(input_file)

    subprocess.check_call(command, stdout=subprocess.PIPE)


def parse_locale_json_file(locale, json_dir):
    """Parses given firmware string json file.

    Args:
        locale: The name of the locale, e.g. "da" or "pt-BR".
        json_dir: Directory containing json output from grit.

    Returns:
        A dictionary for mapping of "name to content" for files to be generated.
    """
    result = {}
    filename = os.path.join(json_dir, STRINGS_JSON_FILE_TMPL.format(locale))
    with open(filename, encoding='utf-8-sig') as input_file:
        for tag, msgdict in json.load(input_file).items():
            msgtext = msgdict['message']
            msgtext = re.sub(CRLF_PATTERN, '\n', msgtext)
            msgtext = re.sub(NEWLINE_PATTERN, NEWLINE_REPLACEMENT, msgtext)
            msgtext = re.sub(MULTIBLANK_PATTERN, ' ', msgtext)
            # Strip any trailing whitespace.  A trailing newline appears to make
            # Pango report a larger layout size than what's actually visible.
            msgtext = msgtext.strip()
            result[tag] = msgtext
    return result


class Converter:
    """Converter for converting sprites, texts, and glyphs to bitmaps.

    Attributes:
        SPRITE_MAX_COLORS (int): Maximum colors to use for converting image
            sprites to bitmaps.
        GLYPH_MAX_COLORS (int): Maximum colors to use for glyph bitmaps.
    """

    # Max colors
    SPRITE_MAX_COLORS = 128
    GLYPH_MAX_COLORS = 7

    def __init__(self, board, formats, board_config, output):
        """Inits converter.

        Args:
            board: Board name.
            formats: A dictionary of string formats.
            board_config: A dictionary of board configurations.
            output: Output directory.
        """
        self.board = board
        self.formats = formats
        self.config = board_config
        self.set_dirs(output)
        self.set_screen()
        self.set_rename_map()
        self.set_locales()
        self.text_max_colors = self.get_text_colors(self.config[KEY_DPI])

    def set_dirs(self, output):
        """Sets board output directory and stage directory.

        Args:
            output: Output directory.
        """
        self.strings_dir = os.path.join(SCRIPT_BASE, 'strings')
        self.sprite_dir = os.path.join(SCRIPT_BASE, 'sprite')
        self.locale_dir = os.path.join(self.strings_dir, 'locale')
        self.output_dir = os.path.join(output, self.board)
        self.output_ro_dir = os.path.join(self.output_dir, 'locale', 'ro')
        self.output_rw_dir = os.path.join(self.output_dir, 'locale', 'rw')
        self.stage_dir = os.path.join(output, '.stage')
        self.stage_grit_dir = os.path.join(self.stage_dir, 'grit')
        self.stage_locale_dir = os.path.join(self.stage_dir, 'locale')
        self.stage_glyph_dir = os.path.join(self.stage_dir, 'glyph')
        self.stage_sprite_dir = os.path.join(self.stage_dir, 'sprite')

    def set_screen(self):
        """Sets screen width and height."""
        self.screen_width, self.screen_height = self.config[KEY_SCREEN]

        self.panel_stretch = fractions.Fraction(1)
        if self.config[KEY_PANEL]:
            # Calculate `panel_stretch`. It's used to shrink images horizontally
            # so that the resulting images will look proportional to the
            # original image on the stretched display. If the display is not
            # stretched, meaning the aspect ratio is same as the screen where
            # images were rendered, no shrinking is performed.
            panel_width, panel_height = self.config[KEY_PANEL]
            self.panel_stretch = fractions.Fraction(
                self.screen_width * panel_height,
                self.screen_height * panel_width)

        if self.panel_stretch > 1:
            raise BuildImageError(
                'Panel aspect ratio (%f) is smaller than screen '
                'aspect ratio (%f). It indicates screen will be '
                'shrunk horizontally. It is currently unsupported.' %
                (panel_width / panel_height,
                 self.screen_width / self.screen_height))

        # Set up square drawing area
        self.canvas_px = min(self.screen_width, self.screen_height)

    def set_rename_map(self):
        """Initializes a dict `self.rename_map` for image renaming.

        For each items in the dict, image `key` will be renamed to `value`.
        """
        is_detachable = os.getenv('DETACHABLE') == '1'
        physical_presence = os.getenv('PHYSICAL_PRESENCE')
        rename_map = {}

        # Navigation instructions
        if is_detachable:
            rename_map.update({
                'nav-button_power': 'nav-key_enter',
                'nav-button_volume_up': 'nav-key_up',
                'nav-button_volume_down': 'nav-key_down',
                'navigate0_tablet': 'navigate0',
                'navigate1_tablet': 'navigate1',
            })
        else:
            rename_map.update({
                'nav-button_power': None,
                'nav-button_volume_up': None,
                'nav-button_volume_down': None,
                'navigate0_tablet': None,
                'navigate1_tablet': None,
            })

        # Physical presence confirmation
        if physical_presence == 'recovery':
            rename_map['rec_to_dev_desc1_phyrec'] = 'rec_to_dev_desc1'
            rename_map['rec_to_dev_desc1_power'] = None
        elif physical_presence == 'power':
            rename_map['rec_to_dev_desc1_phyrec'] = None
            rename_map['rec_to_dev_desc1_power'] = 'rec_to_dev_desc1'
        else:
            rename_map['rec_to_dev_desc1_phyrec'] = None
            rename_map['rec_to_dev_desc1_power'] = None
            if physical_presence != 'keyboard':
                raise BuildImageError(
                    'Invalid physical presence setting %s for board '
                    '%s' % (physical_presence, self.board))

        # Broken screen
        if physical_presence == 'recovery':
            rename_map['broken_desc_phyrec'] = 'broken_desc'
            rename_map['broken_desc_detach'] = None
        elif is_detachable:
            rename_map['broken_desc_phyrec'] = None
            rename_map['broken_desc_detach'] = 'broken_desc'
        else:
            rename_map['broken_desc_phyrec'] = None
            rename_map['broken_desc_detach'] = None

        # SD card
        if not self.config[KEY_SDCARD]:
            rename_map.update({
                'rec_sel_desc1_no_sd':
                'rec_sel_desc1',
                'rec_sel_desc1_no_phone_no_sd':
                'rec_sel_desc1_no_phone',
                'rec_disk_step1_desc0_no_sd':
                'rec_disk_step1_desc0',
            })
        else:
            rename_map.update({
                'rec_sel_desc1_no_sd': None,
                'rec_sel_desc1_no_phone_no_sd': None,
                'rec_disk_step1_desc0_no_sd': None,
            })

        # Check for duplicate new names
        new_names = list(new_name for new_name in rename_map.values()
                         if new_name)
        if len(set(new_names)) != len(new_names):
            raise BuildImageError('Duplicate values found in rename_map')

        # Map new_name to None to skip image generation for it
        for new_name in new_names:
            if new_name not in rename_map:
                rename_map[new_name] = None

        # Print mapping
        print('Rename map:')
        for name, new_name in sorted(rename_map.items()):
            print('  %s => %s' % (name, new_name))

        self.rename_map = rename_map

    def set_locales(self):
        """Sets a list of locales for which localized images are converted."""
        # LOCALES environment variable can override boards.yaml
        env_locales = os.getenv('LOCALES')
        rtl_locales = set(self.config[KEY_RTL])
        if env_locales:
            locales = env_locales.split()
        else:
            locales = self.config[KEY_LOCALES]
            # Check rtl_locales are contained in locales.
            unknown_rtl_locales = rtl_locales - set(locales)
            if unknown_rtl_locales:
                raise BuildImageError('Unknown locales %s in %s' %
                                      (list(unknown_rtl_locales), KEY_RTL))
        self.locales = [
            LocaleInfo(code, code in rtl_locales) for code in locales
        ]

    @classmethod
    def get_text_colors(cls, dpi):
        """Derives maximum text colors from `dpi`."""
        if dpi < 64:
            return 2
        if dpi < 72:
            return 3
        if dpi < 80:
            return 4
        if dpi < 96:
            return 5
        if dpi < 112:
            return 6
        return 7

    def _to_px(self, length, num_lines=1):
        """Converts the relative coordinate to absolute one in pixels."""
        return int(self.canvas_px * length / SCALE_BASE) * num_lines

    @classmethod
    def _get_png_height(cls, png_file):
        # With small DPI, pango-view may generate an empty file
        if os.path.getsize(png_file) == 0:
            return 0
        with Image.open(png_file) as image:
            return image.size[1]

    def get_num_lines(self, file, one_line_dir):
        """Gets the number of lines of text in `file`."""
        name, _ = os.path.splitext(os.path.basename(file))
        png_name = name + '.png'
        multi_line_file = os.path.join(os.path.dirname(file), png_name)
        one_line_file = os.path.join(one_line_dir, png_name)
        # The number of lines is determined by comparing the height of
        # `multi_line_file` with `one_line_file`, where the latter is generated
        # without the '--width' option passed to pango-view.
        height = self._get_png_height(multi_line_file)
        line_height = self._get_png_height(one_line_file)
        return int(round(height / line_height))

    def convert_svg_to_png(self,
                           svg_file,
                           png_file,
                           height,
                           bgcolor,
                           num_lines=1):
        """Converts SVG to PNG file."""
        # If the width/height of the SVG file is specified in points, the
        # rsvg-convert command with default 90DPI will potentially cause the
        # pixels at the right/bottom border of the output image to be
        # transparent (or filled with the specified background color).  This
        # seems like an rsvg-convert issue regarding image scaling.  Therefore,
        # use 72DPI here to avoid the scaling.
        command = [
            'rsvg-convert', '--background-color',
            "'%s'" % bgcolor, '--dpi-x', '72', '--dpi-y', '72', '-o', png_file
        ]
        height_px = self._to_px(height, num_lines)
        if height_px <= 0:
            raise BuildImageError('Height of %r <= 0 (%dpx)' %
                                  (os.path.basename(svg_file), height_px))
        command.extend(['--height', '%d' % height_px])
        command.append(svg_file)
        subprocess.check_call(' '.join(command), shell=True)

    def convert_png_to_bmp(self, png_file, bmp_file, max_colors, num_lines=1):
        """Converts PNG to BMP file."""
        image = Image.open(png_file)

        # Process alpha channel and transparency.
        if image.mode == 'RGBA':
            raise BuildImageError('PNG with RGBA mode is not supported')
        if image.mode == 'P' and 'transparency' in image.info:
            raise BuildImageError('PNG with RGBA palette is not supported')
        if image.mode != 'RGB':
            target = image.convert('RGB')
        else:
            target = image

        width_px, height_px = image.size
        # Stretch image horizontally for stretched display.
        if self.panel_stretch != 1:
            width_px = int(width_px * self.panel_stretch)
            target = target.resize((width_px, height_px), Image.BICUBIC)

        # Export and downsample color space.
        target.convert('P',
                       dither=None,
                       colors=max_colors,
                       palette=Image.ADAPTIVE).save(bmp_file)

        with open(bmp_file, 'rb+') as f:
            f.seek(BMP_HEADER_OFFSET_NUM_LINES)
            f.write(bytearray([num_lines]))

    @classmethod
    def _bisect_dpi(cls, max_dpi, initial_dpi, max_height_px, get_height):
        """Bisects to find the DPI that produces image height `max_height_px`.

        Args:
            max_dpi: Maximum DPI for binary search.
            initial_dpi: Initial DPI to try with in binary search.
                If specified, the value must be no larger than `max_dpi`.
            max_height_px: Maximum (target) height to search for.
            get_height: A function converting DPI to height. The function is
                called once before returning.

        Returns:
            The best integer DPI within [1, `max_dpi`].
        """
        min_dpi = 1
        first_iter = True

        min_height_px = get_height(min_dpi)
        if min_height_px > max_height_px:
            # For some font such as "Noto Sans CJK SC", the generated height
            # cannot go below a certain value. In this case, find max DPI with
            # height_px <= min_height_px.
            while min_dpi < max_dpi:
                if first_iter and initial_dpi:
                    mid_dpi = initial_dpi
                else:
                    mid_dpi = (min_dpi + max_dpi + 1) // 2
                height_px = get_height(mid_dpi)
                if height_px > min_height_px:
                    max_dpi = mid_dpi - 1
                else:
                    min_dpi = mid_dpi
                first_iter = False
            get_height(max_dpi)
            return max_dpi

        # Find min DPI with height_px == max_height_px
        while min_dpi < max_dpi:
            if first_iter and initial_dpi:
                mid_dpi = initial_dpi
            else:
                mid_dpi = (min_dpi + max_dpi) // 2
            height_px = get_height(mid_dpi)
            if height_px == max_height_px:
                return mid_dpi
            if height_px < max_height_px:
                min_dpi = mid_dpi + 1
            else:
                max_dpi = mid_dpi
            first_iter = False
        get_height(min_dpi)
        return min_dpi

    def convert_text_to_image(self,
                              locale,
                              input_file,
                              output_file,
                              font,
                              stage_dir,
                              max_colors,
                              height=None,
                              max_width=None,
                              dpi=None,
                              initial_dpi=None,
                              bgcolor='#000000',
                              fgcolor='#ffffff',
                              use_svg=False):
        """Converts text file `input_file` into image file.

        Because pango-view does not support assigning output format options for
        bitmap, we must create images in SVG/PNG format and then post-process
        them (e.g. convert into BMP by ImageMagick).

        Args:
            locale: Locale (language) to select implicit rendering options. None
                for locale-independent strings.
            input_file: Path of input text file.
            output_file: Path of output image file.
            font: Font name.
            stage_dir: Directory to store intermediate file(s).
            max_colors: Maximum colors to convert to bitmap.
            height: Image height relative to the screen resolution.
            max_width: Maximum image width relative to the screen resolution.
            dpi: DPI value passed to pango-view.
            initial_dpi: Initial DPI to try with in binary search.
            bgcolor: Background color (#rrggbb).
            fgcolor: Foreground color (#rrggbb).
            use_svg: If set to True, generate SVG file. Otherwise, generate PNG
                file.

        Returns:
            Effective DPI, or `None` when not applicable.
        """
        one_line_dir = os.path.join(stage_dir, ONE_LINE_DIR)
        os.makedirs(one_line_dir, exist_ok=True)

        name, _ = os.path.splitext(os.path.basename(input_file))
        svg_file = os.path.join(stage_dir, name + '.svg')
        png_file = os.path.join(stage_dir, name + '.png')
        png_file_one_line = os.path.join(one_line_dir, name + '.png')

        def get_one_line_png_height(dpi):
            """Generates a one-line PNG with `dpi` and returns its height."""
            run_pango_view(input_file, png_file_one_line, locale, font, height,
                           0, dpi, bgcolor, fgcolor)
            return self._get_png_height(png_file_one_line)

        if use_svg:
            run_pango_view(input_file,
                           svg_file,
                           locale,
                           font,
                           height,
                           0,
                           dpi,
                           bgcolor,
                           fgcolor,
                           hinting='none')
            self.convert_svg_to_png(svg_file, png_file, height, bgcolor)
            self.convert_png_to_bmp(png_file, output_file, max_colors)
            return None

        if not dpi:
            raise BuildImageError('DPI must be specified with use_svg=False')
        eff_dpi = dpi
        max_height_px = self._to_px(height)
        height_px = get_one_line_png_height(dpi)
        if height_px > max_height_px:
            eff_dpi = self._bisect_dpi(dpi, initial_dpi, max_height_px,
                                       get_one_line_png_height)
        if max_width:
            # NOTE: With the same DPI, the height of multi-line PNG is not
            # necessarily a multiple of the height of one-line PNG. Therefore,
            # even with the binary search, the height of the resulting
            # multi-line PNG might be less than "one_line_height * num_lines".
            # We cannot binary-search DPI for multi-line PNGs because
            # "num_lines" is dependent on DPI.
            run_pango_view(input_file, png_file, locale, font, height,
                           max_width, eff_dpi, bgcolor, fgcolor)
            num_lines = self.get_num_lines(png_file, one_line_dir)
        else:
            png_file = png_file_one_line
            num_lines = 1
        self.convert_png_to_bmp(png_file,
                                output_file,
                                max_colors,
                                num_lines=num_lines)
        return eff_dpi

    def convert_sprite_images(self):
        """Converts sprite images."""
        names = self.formats[KEY_SPRITE_FILES]
        styles = self.formats[KEY_STYLES]
        # Check redundant images
        for filename in glob.glob(os.path.join(self.sprite_dir, SVG_FILES)):
            name, _ = os.path.splitext(os.path.basename(filename))
            if name not in names:
                raise BuildImageError('Sprite image %r not specified in %s' %
                                      (filename, FORMAT_FILE))
        # Convert images
        os.makedirs(self.stage_sprite_dir, exist_ok=True)
        for name, category in names.items():
            new_name = self.rename_map.get(name, name)
            if not new_name:
                continue
            style = get_config_with_defaults(styles, category)
            svg_file = os.path.join(self.sprite_dir, name + '.svg')
            png_file = os.path.join(self.stage_sprite_dir, name + '.png')
            bmp_file = os.path.join(self.output_dir, new_name + '.bmp')
            height = style[KEY_HEIGHT]
            bgcolor = style[KEY_BGCOLOR]
            self.convert_svg_to_png(svg_file, png_file, height, bgcolor)
            self.convert_png_to_bmp(png_file, bmp_file, self.SPRITE_MAX_COLORS)

    def build_generic_strings(self):
        """Builds images of generic (locale-independent) strings."""
        dpi = self.config[KEY_DPI]

        names = self.formats[KEY_GENERIC_FILES]
        styles = self.formats[KEY_STYLES]
        fonts = self.formats[KEY_FONTS]
        default_font = fonts[KEY_DEFAULT]

        for txt_file in glob.glob(os.path.join(self.strings_dir, '*.txt')):
            name, _ = os.path.splitext(os.path.basename(txt_file))
            new_name = self.rename_map.get(name, name)
            if not new_name:
                continue
            bmp_file = os.path.join(self.output_dir, new_name + '.bmp')
            category = names[name]
            style = get_config_with_defaults(styles, category)
            if style[KEY_MAX_WIDTH]:
                # Setting max_width causes left/right alignment of the text.
                # However, generic strings are locale independent, and hence
                # shouldn't have text alignment within the bitmap.
                raise BuildImageError(
                    '{}: {!r} should be null for generic strings'.format(
                        name, KEY_MAX_WIDTH))
            self.convert_text_to_image(None,
                                       txt_file,
                                       bmp_file,
                                       default_font,
                                       self.stage_dir,
                                       self.text_max_colors,
                                       height=style[KEY_HEIGHT],
                                       max_width=None,
                                       dpi=dpi,
                                       bgcolor=style[KEY_BGCOLOR],
                                       fgcolor=style[KEY_FGCOLOR])

    def build_locale(self, locale, names):
        """Builds images of strings for `locale`."""
        dpi = self.config[KEY_DPI]
        styles = self.formats[KEY_STYLES]
        fonts = self.formats[KEY_FONTS]
        font = fonts.get(locale, fonts[KEY_DEFAULT])
        inputs = parse_locale_json_file(locale, self.stage_grit_dir)

        # Walk locale dir to add pre-generated texts such as language names.
        for txt_file in glob.glob(
                os.path.join(self.locale_dir, locale, '*.txt')):
            name, _ = os.path.splitext(os.path.basename(txt_file))
            with open(txt_file, 'r', encoding='utf-8-sig') as f:
                inputs[name] = f.read().strip()

        stage_dir = os.path.join(self.stage_locale_dir, locale)
        os.makedirs(stage_dir, exist_ok=True)
        output_dir = os.path.join(self.output_ro_dir, locale)
        os.makedirs(output_dir, exist_ok=True)

        eff_dpi_counters = defaultdict(Counter)
        eff_dpi_counter = None
        results = []
        for name, category in sorted(names.items()):
            # Ignore missing translation
            if locale != 'en' and name not in inputs:
                continue

            new_name = self.rename_map.get(name, name)
            if not new_name:
                continue
            output_file = os.path.join(output_dir, new_name + '.bmp')

            # Write to text file
            text_file = os.path.join(stage_dir, name + '.txt')
            with open(text_file, 'w', encoding='utf-8-sig') as f:
                f.write(inputs[name] + '\n')

            # Convert text to image
            style = get_config_with_defaults(styles, category)
            height = style[KEY_HEIGHT]
            eff_dpi_counter = eff_dpi_counters[height]
            if eff_dpi_counter:
                # Find the effective DPI that appears most times for `height`.
                # This avoid doing the same binary search again and again. In
                # case of a tie, pick the largest DPI.
                best_eff_dpi = max(eff_dpi_counter,
                                   key=lambda dpi: (eff_dpi_counter[dpi], dpi))
            else:
                best_eff_dpi = None
            eff_dpi = self.convert_text_to_image(
                locale,
                text_file,
                output_file,
                font,
                stage_dir,
                self.text_max_colors,
                height=height,
                max_width=style[KEY_MAX_WIDTH],
                dpi=dpi,
                initial_dpi=best_eff_dpi,
                bgcolor=style[KEY_BGCOLOR],
                fgcolor=style[KEY_FGCOLOR])
            eff_dpi_counter[eff_dpi] += 1
            assert eff_dpi <= dpi
            if eff_dpi != dpi:
                results.append(eff_dpi)
        return results

    def _check_text_width(self, names):
        """Checks if text image will exceed the drawing area at runtime."""
        styles = self.formats[KEY_STYLES]

        for locale_info in self.locales:
            locale = locale_info.code
            ro_locale_dir = os.path.join(self.output_ro_dir, locale)
            for filename in glob.glob(os.path.join(ro_locale_dir, '*.bmp')):
                name, _ = os.path.splitext(os.path.basename(filename))
                category = names[name]
                style = get_config_with_defaults(styles, category)
                height = style[KEY_HEIGHT]
                max_width = style[KEY_MAX_WIDTH]
                if not max_width:
                    continue
                max_width_px = self._to_px(max_width)
                with open(filename, 'rb') as f:
                    f.seek(BMP_HEADER_OFFSET_NUM_LINES)
                    num_lines = f.read(1)[0]
                height_px = self._to_px(height * num_lines)
                with Image.open(filename) as image:
                    width_px = height_px * image.size[0] // image.size[1]
                if width_px > max_width_px:
                    raise BuildImageError(
                        '%s: Image width %dpx greater than max width '
                        '%dpx' % (filename, width_px, max_width_px))

    def _copy_missing_bitmaps(self):
        """Copies missing (not yet translated) strings from locale 'en'."""
        en_files = glob.glob(os.path.join(self.output_ro_dir, 'en', '*.bmp'))
        for locale_info in self.locales:
            locale = locale_info.code
            if locale == 'en':
                continue
            ro_locale_dir = os.path.join(self.output_ro_dir, locale)
            for en_file in en_files:
                filename = os.path.basename(en_file)
                locale_file = os.path.join(ro_locale_dir, filename)
                if not os.path.isfile(locale_file):
                    print("WARNING: Locale '%s': copying '%s'" %
                          (locale, filename))
                    shutil.copyfile(en_file, locale_file)

    def build_localized_strings(self):
        """Builds images of localized strings."""
        # Sources are one .grd file with identifiers chosen by engineers and
        # corresponding English texts, as well as a set of .xtb files (one for
        # each language other than US English) with a mapping from hash to
        # translation. Because the keys in the .xtb files are a hash of the
        # English source text, rather than our identifiers, such as
        # "btn_cancel", we use the "grit" command line tool to process the .grd
        # and .xtb files, producing a set of .json files mapping our identifier
        # to the translated string, one for every language including US English.

        # This invokes the grit build command to generate JSON files from the
        # XTB files containing translations.  The results are placed in
        # `self.stage_grit_dir` as specified in firmware_strings.grd, i.e. one
        # JSON file per locale.
        os.makedirs(self.stage_grit_dir, exist_ok=True)
        subprocess.check_call([
            'grit',
            '-i',
            os.path.join(self.locale_dir, STRINGS_GRD_FILE),
            'build',
            '-o',
            self.stage_grit_dir,
        ])

        # Make a copy to avoid modifying `self.formats`
        names = copy.deepcopy(self.formats[KEY_LOCALIZED_FILES])
        if DIAGNOSTIC_UI:
            names.update(self.formats[KEY_DIAGNOSTIC_FILES])

        executor = ProcessPoolExecutor()
        futures = []
        for locale_info in self.locales:
            locale = locale_info.code
            print(locale, end=' ', flush=True)
            futures.append(executor.submit(self.build_locale, locale, names))

        print()

        try:
            results = [future.result() for future in futures]
        except KeyboardInterrupt:
            executor.shutdown(wait=False)
            sys.exit('Aborted by user')
        else:
            executor.shutdown()

        effective_dpi = [dpi for r in results for dpi in r if dpi]
        if effective_dpi:
            print(
                'Reducing effective DPI to %d, limited by screen resolution' %
                max(effective_dpi))

        self._check_text_width(names)
        self._copy_missing_bitmaps()

    def move_language_images(self):
        """Renames language bitmaps and move to self.output_dir.

        The directory self.output_dir contains locale-independent images, and is
        used for creating vbgfx.bin by archive_images.py.
        """
        for locale_info in self.locales:
            locale = locale_info.code
            ro_locale_dir = os.path.join(self.output_ro_dir, locale)
            old_file = os.path.join(ro_locale_dir, 'language.bmp')
            new_file = os.path.join(self.output_dir,
                                    'language_%s.bmp' % locale)
            if os.path.exists(new_file):
                raise BuildImageError('File already exists: %s' % new_file)
            shutil.move(old_file, new_file)

    def build_glyphs(self):
        """Builds glyphs of ascii characters."""
        os.makedirs(self.stage_glyph_dir, exist_ok=True)
        output_dir = os.path.join(self.output_dir, 'glyph')
        os.makedirs(output_dir)
        executor = ProcessPoolExecutor()
        futures = []
        for c in range(ord(' '), ord('~') + 1):
            name = f'idx{c:03d}_{c:02x}'
            txt_file = os.path.join(self.stage_glyph_dir, name + '.txt')
            with open(txt_file, 'w', encoding='ascii') as f:
                f.write(chr(c))
                f.write('\n')
            output_file = os.path.join(output_dir, name + '.bmp')
            futures.append(
                executor.submit(self.convert_text_to_image,
                                None,
                                txt_file,
                                output_file,
                                GLYPH_FONT,
                                self.stage_glyph_dir,
                                self.GLYPH_MAX_COLORS,
                                height=DEFAULT_GLYPH_HEIGHT,
                                use_svg=True))
        for future in futures:
            future.result()
        executor.shutdown()

    def copy_images_to_rw(self):
        """Copies localized images specified in boards.yaml for RW override."""
        if not self.config[KEY_RW_OVERRIDE]:
            print('  No localized images are specified for RW, skipping')
            return

        for locale_info in self.locales:
            locale = locale_info.code
            ro_locale_dir = os.path.join(self.output_ro_dir, locale)
            rw_locale_dir = os.path.join(self.output_rw_dir, locale)
            os.makedirs(rw_locale_dir)

            for name in self.config[KEY_RW_OVERRIDE]:
                ro_src = os.path.join(ro_locale_dir, name + '.bmp')
                rw_dst = os.path.join(rw_locale_dir, name + '.bmp')
                shutil.copyfile(ro_src, rw_dst)

    def create_locale_list(self):
        """Creates locale list as a CSV file.

        Each line in the file is of format "code,rtl", where
        - "code": language code of the locale
        - "rtl": "1" for right-to-left language, "0" otherwise
        """
        with open(os.path.join(self.output_dir, 'locales'), 'w') as f:
            for locale_info in self.locales:
                f.write('{},{}\n'.format(locale_info.code,
                                         int(locale_info.rtl)))

    def build(self):
        """Builds all images required by a board."""
        # Clean up output/stage directories
        for path in (self.output_dir, self.stage_dir):
            if os.path.exists(path):
                shutil.rmtree(path)
        os.makedirs(self.output_dir)
        os.makedirs(self.stage_dir)

        print('Converting sprite images...')
        self.convert_sprite_images()

        print('Building generic strings...')
        self.build_generic_strings()

        print('Building localized strings...')
        self.build_localized_strings()

        print('Moving language images to locale-independent directory...')
        self.move_language_images()

        print('Creating locale list file...')
        self.create_locale_list()

        print('Building glyphs...')
        self.build_glyphs()

        print('Copying specified images to RW packing directory...')
        self.copy_images_to_rw()


def main():
    """Builds bitmaps for firmware screens."""
    parser = argparse.ArgumentParser()
    parser.add_argument('board', help='Target board')
    args = parser.parse_args()
    board = args.board

    with open(FORMAT_FILE, encoding='utf-8') as f:
        formats = yaml.load(f)
    board_config = load_board_config(BOARDS_CONFIG_FILE, board)

    print('Building for ' + board)
    check_fonts(formats[KEY_FONTS])
    print('Output dir: ' + OUTPUT_DIR)
    converter = Converter(board, formats, board_config, OUTPUT_DIR)
    converter.build()


if __name__ == '__main__':
    main()