label_printer/check_print_area.py

"""
Measure the PT-E560BT driver's page and printable area.

Context: the PDF we send is verified to be exactly 65 x 24 mm, but the label
prints at roughly 25 x 17 mm. That points at the driver rather than our PDF, so
this reads the driver's own coordinate system instead of guessing.

GetDeviceCaps() is authoritative:
  HORZSIZE / VERTSIZE    -> physical page size, in millimetres
  HORZRES / VERTRES      -> printable area, in device dots
  PHYSICALWIDTH / HEIGHT -> full page, in device dots
  PHYSICALOFFSETX / Y    -> where the printable area starts (unprintable margin)
"""

import os
import sys

import win32ui

PRINTER = "Brother PT-E560BT"
CONTROL = "Microsoft Print to PDF"  # control: a normal printer, to sanity-check the method

HORZSIZE, VERTSIZE = 4, 6
HORZRES, VERTRES = 8, 10
LOGPIXELSX, LOGPIXELSY = 88, 90
PHYSICALWIDTH, PHYSICALHEIGHT = 110, 111
PHYSICALOFFSETX, PHYSICALOFFSETY = 112, 113

CAP_INDICES = {
    "HORZSIZE": HORZSIZE,
    "VERTSIZE": VERTSIZE,
    "HORZRES": HORZRES,
    "VERTRES": VERTRES,
    "LOGPIXELSX": LOGPIXELSX,
    "LOGPIXELSY": LOGPIXELSY,
    "PHYSICALWIDTH": PHYSICALWIDTH,
    "PHYSICALHEIGHT": PHYSICALHEIGHT,
    "PHYSICALOFFSETX": PHYSICALOFFSETX,
    "PHYSICALOFFSETY": PHYSICALOFFSETY,
}

# What we intend to print (our PDF page, and the label content inside it).
PAGE_MM = (65.0, 24.0)
CONTENT_MM = (63.0, 20.0)


def dots_to_mm(dots, dpi):
    return dots / dpi * 25.4 if dpi else 0.0


def measure(printer, devmode=None):
    """Return the driver's caps dict, or None if the DC could not be created."""
    try:
        hdc = win32ui.CreateDC()
        hdc.CreatePrinterDC(printer)
    except Exception as exc:  # noqa: BLE001
        print(f"  CreatePrinterDC failed: {exc}")
        return None

    try:
        caps = {name: hdc.GetDeviceCaps(idx) for name, idx in CAP_INDICES.items()}
    finally:
        try:
            hdc.DeleteDC()
        except Exception:  # noqa: BLE001
            pass

    dpix = caps["LOGPIXELSX"] or 1
    dpiy = caps["LOGPIXELSY"] or 1

    print(f"\n{printer}")
    print(f"  resolution          : {dpix} x {dpiy} dpi")
    print(f"  physical page       : {caps['HORZSIZE']} x {caps['VERTSIZE']} mm")
    print(
        f"  printable area      : {caps['HORZRES']} x {caps['VERTRES']} dots = "
        f"{dots_to_mm(caps['HORZRES'], dpix):.2f} x {dots_to_mm(caps['VERTRES'], dpiy):.2f} mm"
    )
    print(
        f"  physical (dots)     : {caps['PHYSICALWIDTH']} x {caps['PHYSICALHEIGHT']} = "
        f"{dots_to_mm(caps['PHYSICALWIDTH'], dpix):.2f} x "
        f"{dots_to_mm(caps['PHYSICALHEIGHT'], dpiy):.2f} mm"
    )
    print(
        f"  printable origin    : {caps['PHYSICALOFFSETX']} x {caps['PHYSICALOFFSETY']} dots = "
        f"{dots_to_mm(caps['PHYSICALOFFSETX'], dpix):.2f} x "
        f"{dots_to_mm(caps['PHYSICALOFFSETY'], dpiy):.2f} mm"
    )
    return caps


def verdict(caps):
    """Explain whether the driver's page matches what we send."""
    dpix = caps["LOGPIXELSX"] or 1
    dpiy = caps["LOGPIXELSY"] or 1
    w = dots_to_mm(caps["PHYSICALWIDTH"], dpix)
    h = dots_to_mm(caps["PHYSICALHEIGHT"], dpiy)

    print(f"\n  VERDICT for {PAGE_MM[0]:.0f} x {PAGE_MM[1]:.0f} mm page:")
    if abs(w - PAGE_MM[0]) < 1.0 and abs(h - PAGE_MM[1]) < 1.0:
        print("    driver page matches our PDF -> driver has nothing to rescale")
    else:
        print(f"    driver page is {w:.2f} x {h:.2f} mm, NOT {PAGE_MM[0]} x {PAGE_MM[1]} mm")
        print(f"    implied scale: x{PAGE_MM[0] / w:.3f} by y{PAGE_MM[1] / h:.3f}")

        # Distinguish 'fit' (uniform) from 'stretch' (non-uniform).
        sx, sy = PAGE_MM[0] / w, PAGE_MM[1] / h
        if abs(sx - sy) < 0.02:
            print("    uniform scale -> driver is using 'fit'")
        else:
            print("    NON-UNIFORM scale -> driver is using 'stretch'; this distorts")

    # Does the reported printable area match the 25 x 17 mm that actually printed?
    pw = dots_to_mm(caps["HORZRES"], dpix)
    ph = dots_to_mm(caps["VERTRES"], dpiy)
    print(f"    printable area {pw:.2f} x {ph:.2f} mm")
    if abs(pw - 25.0) < 3.0 or abs(ph - 17.0) < 3.0:
        print("    ^ this is close to the 25 x 17 mm actually observed on tape")


def main() -> int:
    print("=" * 72)
    print("DRIVER PRINT AREA")
    print("=" * 72)
    print(f"Our PDF page    : {PAGE_MM[0]:.1f} x {PAGE_MM[1]:.1f} mm")
    print(f"Label content   : {CONTENT_MM[0]:.1f} x {CONTENT_MM[1]:.1f} mm")

    caps = measure(PRINTER)
    if caps is None:
        return 1
    verdict(caps)

    print("\n" + "-" * 72)
    print("CONTROL (method sanity check)")
    print("-" * 72)
    measure(CONTROL)

    print("\n" + "=" * 72)
    return 0


if __name__ == "__main__":
    raise SystemExit(main())