Backup font for missing characters when drawing text

[Markxy]

Description of the request

I want to use a specific font but also draw characters which are not available in that font. Replace them with characters from another "generic" font, like Arial-Bold for example.
Similarly to how web browsers work when they are missing characters from fonts - the OS fills that void from a default font.

from PIL import Image, ImageFont, ImageDraw


temp_canvas = Image.new("RGBA", (1200, 300), (255, 255, 255, 255))
draw_canvas = ImageDraw.Draw(temp_canvas, "RGBA")

font = ImageFont.truetype(r"C:\fonts\BarlowSemiCondensed-Bold.ttf", size=150)
text_string = "hello ಠಠ world"

draw_canvas.text((100, 100), text_string, fill="#000000", font=font)

temp_canvas.show()

The output is:

Proposed solution

Add an argument to ImageDraw.Draw().text() like backup_font , which would be used when the first font doesn't have the character specified in text_string . Like ಠ in this example

[nulano]

I don't think FreeType (the library Pillow uses to load fonts) is able to combine multiple typefaces into one. This change would be simple with basic layout (Pillow can try loading each glyph from a list of fonts until one succeeds), but Raqm (used for complex scripts) seems to require passing a single typeface to be used for the whole string. So for complex layout this would require a change in Raqm, either upstream or by including a vendored change in Pillow.

The latter could help with some of the distribution issues that have appeared in the past (the dynamic loading would be moved to FriBiDi; users would only need to install LGPL-licensed FriBiDi to enable complex text, not Raqm which is sometimes available in an outdated and unsupported version in some linux distributions). It could also potentially help #3066. Edit: #3066 is now fixed by including a vendored build of Raqm in binary wheels.

As for the API to use here, I would propose ImageFont.truetype_family(font1, font2, font3, ...) to create a compound font, which would get special handling in the C code.

[LateusBetelgeuse]

This can be specially helpful with emojis. Many emojis font only contains emojis, and the ones that contains regular glyph have styles that can break the image/poster paradigm that one wants to achieve. However this can be tricky because all color emoji fonts that I've tested so far requires exactly a size of 109, which would require super-sampling and then smooth resizing.

[voussoir]

Hi, I'm interested in this problem too.

At the moment I'm using a workaround based on this stackoverflow answer.

from fontTools.ttLib import TTFont

def has_glyph(font, glyph):
    for table in font['cmap'].tables:
        if ord(glyph) in table.cmap.keys():
            return True
    log.debug('%s does not have %s', font, glyph)
    return False

def determine_font(text):
    text = stringtools.remove_control_characters(text)
    font_options = [
        'C:\\Windows\\Fonts\\NotoSansKR-Bold.otf',
        'C:\\Windows\\Fonts\\NotoSansSC-Bold.otf',
        'C:\\Windows\\Fonts\\NotoSansJP-Bold.otf',
    ]
    for font_name in font_options:
        font = TTFont(font_name)
        if all(has_glyph(font, c) for c in text):
            return font_name
    raise Exception(f'No suitable font for {text}.')

However, this still doesn't work when none of the fonts contain all of the glyphs. I learned that Noto Arabic doesn't contain the ascii letters!

I don't know anything about how web browsers or file explorers handle font stacking, but it would be great if we could get some of that behavior by default in PIL. Anyway just thought I'd share that snippet.

[0xAA55]

After searching the internet, I've got a workaround by merging font files into a single font file.

By reading merge_fonts.py, I think the core code about merging font files in python is the following (you may have to install fontTools).

from fontTools import ttLib, merge

def make_font(font_list, output_to):
    merger = merge.Merger()
    font = merger.merge(font_list)
    metrics = read_line_metrics(ttLib.TTFont(font_list[0]))
    set_line_metrics(font, metrics)
    font.save(output_to)
    font.close()

[khaledmsm]

After searching the internet, I've got a workaround by merging font files into a single font file.

By reading merge_fonts.py, I think the core code about merging font files in python is the following (you may have to install fontTools).

from fontTools import ttLib, merge

def make_font(font_list, output_to):
    merger = merge.Merger()
    font = merger.merge(font_list)
    metrics = read_line_metrics(ttLib.TTFont(font_list[0]))
    set_line_metrics(font, metrics)
    font.save(output_to)
    font.close()

do you have actual code
because this one isn't clear