generate a png with a single character glyph, border and background

generate_glyph_pngs.py

#!/usr/bin/python3
'''
to be used to generate a pile of images for import to deployment-prep commons
requires: pycairo, Pillow >= 6.0.0
'''
import sys
import cairo
from PIL import Image
from PIL.PngImagePlugin import PngInfo


def write_png(font, canvas_width, output_path, glyph, verbose=False):
    '''
    given an output file path, a font face, the width of the
    output image (height will be same as the width) and the glyph
    to be displayed, create an image with a 2 pixel border, a yellowish-tan
    background and the centered glyph in black.
    '''
    canvas_height = canvas_width

    # for bitmap output. all units in pixels
    surface = cairo.ImageSurface(cairo.FORMAT_RGB24, canvas_width, canvas_height)
    ctx = cairo.Context(surface)

    # background
    ctx.rectangle(0, 0, canvas_width - 1, canvas_height - 1)
    ctx.set_source_rgb(0.9, 0.8, 0.6)
    ctx.fill()
    # border
    ctx.set_line_width(2)
    ctx.set_source_rgb(0.1, 0.1, 0.1)
    ctx.stroke()

    # glyph
    ctx.set_source_rgb(0, 0, 0)
    ctx.set_font_size(canvas_width - 2)
    ctx.select_font_face(font, cairo.FONT_SLANT_NORMAL, cairo.FONT_WEIGHT_BOLD)
    (x_bearing, y_bearing, text_width, text_height, _dx, _dy) = ctx.text_extents(glyph)
    if verbose:
        print("x_advance is", _dx, "and y_advance is", _dy)
        print("text_width is", text_width, "and text_height is", text_height)
        print("x_bearing is", x_bearing, "and y_bearing is", y_bearing)

    options = cairo.FontOptions()
    options.set_antialias(cairo.ANTIALIAS_DEFAULT)
    ctx.set_font_options(options)

    ctx.move_to(canvas_width/2 - text_width/2 - x_bearing,
                canvas_height/2 - text_height/2 - y_bearing)
    ctx.show_text(glyph)

    surface.write_to_png(output_path)


def usage(message=None):
    '''display usage info about this script'''
    if message is not None:
        print(message)
    print("Usage: generate_glyph_pngs.py font-name canvas-width-in-px "
          "output-path start-glyph end-glyph")
    print("Canvas width and height are the same, font is always bold weight, colors are fixed")
    print("Output-path is the relative or absolute path including the file basename but not")
    print("the '.png' suffix. The glyph to be printed will be concatenated to the filename.")
    print("Example use: python3 generate_glyph_pngs.py 'Noto Serif CJK JP' 32 myfile 見myfile")
    print("         or: python3 generate_glyph_pngs.py 'Noto Serif CJK JP' 32 myfile 0xe8a68b")
    sys.exit(1)


def convert_hex(text):
    '''
    if the text is a string of hex bytes, convert that to unicode
    and use it instead
    '''
    if not text.startswith('0x'):
        return text

    text = text[2:]
    hex_digits = ''.join([letter for letter in text if letter not in 'abcdefABCDEF1234567890'])
    if hex_digits:
        return text
    if len(text) % 2:
        return text

    # we have a valid hex string, let's convert it then
    return bytes.fromhex(text).decode('utf8')


def convert_path(path, glyph):
    '''
    add - + glyph to the filename, and make sure that the
    .png suffix is added afterwards
    '''
    if path.endswith('.png'):
        path = path[0:-4]
    return path + '-' + glyph + '.png'


def add_png_metadata(path, glyph, metadata, verbose=False):
    '''
    given the path to a png file and the glyph it contains,
    write appropriate metadata fields into the file
    '''
    metadata['Description'] = metadata['_Description_tmpl'].format(glyph=glyph)
    metadata['Title'] = metadata['_Title_tmpl'].format(glyph=glyph)

    with Image.open(path) as image:
        info = PngInfo()
        for entry in ["Author", "Description", "Title", "Software"]:
            if not entry.startswith('_'):
                info.add_itxt(entry, metadata[entry], "en", entry)
        image.save('new-' + path, pnginfo=info)

        if verbose:
            with Image.open('new-' + path) as image:
                print("new image is", 'new-' + path)
                print(image.info)


def do_main():
    '''
    entry point
    '''
    # change this if you need to debug something
    verbose = False

    if len(sys.argv) < 5 or len(sys.argv) > 6:
        usage('missing or extra arg(s)')

    font = sys.argv[1]

    canvas_width = sys.argv[2]
    if not canvas_width.isdigit():
        usage('width must be the number of pixels')

    output_path = sys.argv[3]

    start_glyph = sys.argv[4]
    end_glyph = start_glyph
    if len(sys.argv) == 6:
        end_glyph = sys.argv[5]

    render_info = "rendered from {font} with black border on golden-yellow background".format(
        font=font)
    metadata = {
        'Author': "Ariel Glenn",
        'Software': "pycairo and pillow",
        '_Description_tmpl': "Character {glyph} " + render_info,
        '_Title_tmpl': "Icon_for_char_{glyph}_black_gold_32x32.png"
    }

    for glyph in range(ord(convert_hex(start_glyph)), ord(convert_hex(end_glyph)) + 1):
        glyph = chr(glyph)
        file_path = convert_path(output_path, glyph)
        write_png(font, int(canvas_width), file_path, glyph, verbose)
        add_png_metadata(file_path, glyph, metadata, verbose)


if __name__ == '__main__':
    do_main()