make_marker.py

"""Generate a printable ArUco marker for wall measurement.

Run:  ./venv/bin/python make_marker.py
Output:  aruco_marker_60mm_A4.pdf  (and a .png preview)

Print the PDF at 100% / "Actual size" (no scaling, no "fit to page"). Then
verify with a ruler that the printed black square is exactly 6.0 cm across.
If it is off, scaling was applied — reprint, or pass the real measured size
to the app's "marker size" field.
"""

from __future__ import annotations

import cv2
import numpy as np
from PIL import Image, ImageDraw, ImageFont

import aruco_scale

DPI = 300
MM_PER_INCH = 25.4
MARKER_MM = aruco_scale.DEFAULT_MARKER_LENGTH_MM   # 120 mm
MARKER_ID = aruco_scale.DEFAULT_MARKER_ID          # 0

A4_W_MM, A4_H_MM = 210.0, 297.0


def mm_to_px(mm: float) -> int:
    return int(round(mm / MM_PER_INCH * DPI))


def _font(size_px: int) -> ImageFont.FreeTypeFont:
    for path in ("/System/Library/Fonts/Supplemental/Arial.ttf",
                 "/System/Library/Fonts/Helvetica.ttc",
                 "/Library/Fonts/Arial.ttf"):
        try:
            return ImageFont.truetype(path, size_px)
        except OSError:
            continue
    return ImageFont.load_default()


def build_marker_image(side_px: int) -> Image.Image:
    """Render the ArUco marker (6x6 modules) crisply at `side_px`."""
    modules = 6  # 4x4 data + 1-module black border each side
    hires = modules * 200
    raw = cv2.aruco.generateImageMarker(aruco_scale.get_dictionary(),
                                        MARKER_ID, hires)
    return Image.fromarray(raw).resize((side_px, side_px), Image.NEAREST)


def main() -> None:
    page = Image.new("RGB", (mm_to_px(A4_W_MM), mm_to_px(A4_H_MM)), "white")
    draw = ImageDraw.Draw(page)
    cx = page.width // 2

    title = _font(mm_to_px(7))
    body = _font(mm_to_px(4.2))
    small = _font(mm_to_px(3.4))

    def centered(y, text, font, fill="black"):
        w = draw.textlength(text, font=font)
        draw.text((cx - w / 2, y), text, font=font, fill=fill)

    y = mm_to_px(15)
    centered(y, "Crack Measurement - ArUco Scale Marker", title)
    y += mm_to_px(11)
    centered(y, "1. Print this page at 100% / Actual Size (no scaling).", body)
    y += mm_to_px(6)
    centered(y, "2. Tape it FLAT on the wall, beside the crack, facing the camera.", body)
    y += mm_to_px(6)
    centered(y, "3. Photograph wall + marker together, then upload to the app.", body)
    y += mm_to_px(10)

    # The marker, with a white quiet zone the printed page already provides.
    side_px = mm_to_px(MARKER_MM)
    marker = build_marker_image(side_px)
    mx, my = cx - side_px // 2, y
    page.paste(marker, (mx, my))

    # Dimension callout under the marker.
    yb = my + side_px + mm_to_px(4)
    draw.line([(mx, yb), (mx + side_px, yb)], fill="black", width=3)
    for ex in (mx, mx + side_px):
        draw.line([(ex, yb - mm_to_px(2)), (ex, yb + mm_to_px(2))],
                  fill="black", width=3)
    centered(yb + mm_to_px(3),
             f"Black square = {MARKER_MM:.0f} mm  ({MARKER_MM/10:.1f} cm)", body)

    y = yb + mm_to_px(14)
    centered(y, f"Dictionary: DICT_4X4_50      Marker ID: {MARKER_ID}", small)
    y += mm_to_px(10)

    # Independent 100 mm print-scale check ruler.
    centered(y, "Print check - this line must measure exactly 10.0 cm:", small)
    y += mm_to_px(6)
    ruler_px = mm_to_px(100.0)
    rx = cx - ruler_px // 2
    draw.line([(rx, y), (rx + ruler_px, y)], fill="black", width=3)
    for i in range(11):  # cm ticks
        tx = rx + mm_to_px(10.0 * i)
        th = mm_to_px(3.5 if i % 5 == 0 else 2.0)
        draw.line([(tx, y - th), (tx, y + th)], fill="black", width=2)
    y += mm_to_px(8)
    centered(y, "If it is not 10.0 cm, your printer rescaled the page - "
                "reprint without scaling.", small)

    # Save the PDF as a 1-bit (black/white) page: lossless CCITT compression,
    # crisp marker edges, small file. The page is pure line art so nothing
    # is lost. dither=NONE keeps text edges clean instead of speckled.
    stem = f"aruco_marker_{MARKER_MM:.0f}mm_A4"
    page.save(f"{stem}.png", dpi=(DPI, DPI))
    page.convert("1", dither=Image.NONE).save(
        f"{stem}.pdf", resolution=float(DPI))
    print(f"Wrote {stem}.pdf  and  {stem}.png")
    print(f"Marker: DICT_4X4_50  id={MARKER_ID}  side={MARKER_MM:.0f} mm")


if __name__ == "__main__":
    main()