Quick script to overlay CoreText vs HB's own shaper for tracking

track_ot_coretext.py

#!/usr/bin/env python3
import subprocess
from PIL import Image, ImageOps
import io

font_ptem_sizes = [
    6,
    9,
    10,
    11,
    12,
    13,
    14,
    15,
    16,
    17,
    20,
    22,
    28,
    32,
    36,
    50,
    64,
    80,
    100,
    138,
]
shapers = ["ot", "coretext"]
shape_text = "www"
font_path = "/System/Library/Fonts/SFNSText.ttf"
features = "-kern"

images = []
for font_ptem_size in font_ptem_sizes:
    for shaper in shapers:
        proc = subprocess.Popen(
            [
                "./hb-view",
                "--features=%s" % features,
                "--font-ptem=%d" % font_ptem_size,
                "--font-size=256",
                "--shaper=%s" % shaper,
                font_path,
                shape_text,
            ],
            shell=False,
            stdout=subprocess.PIPE,
        )
        images.append(Image.open(io.BytesIO(proc.communicate()[0])))

max_x = 0
acc_y = 0
for image in images:
    max_x = max(max_x, image.getbbox()[2])
    acc_y += image.getbbox()[3]
composite_image = Image.new("RGBA", (max_x, acc_y))
insert_position = 0
for image_ot, image_coretext in zip(images[::2], images[1::2]):
    merged_size = (
        max(image_ot.width, image_coretext.width),
        max(image_ot.height, image_coretext.height),
    )
    alpha_blended = Image.new("RGBA", merged_size)
    alpha_blended.paste(
        ImageOps.colorize(image_coretext, "Green", "White"),
        (0, 0),
        Image.new("L", image_coretext.size, 255),
    )
    alpha_blended.paste(
        ImageOps.colorize(image_ot, "Red", "White"),
        (0, 0),
        Image.new("L", image_ot.size, 100),
    )
    composite_image.paste(alpha_blended, (0, insert_position))
    insert_position += merged_size[1]
composite_image.save("coretext_green_ot_red.png")