#!/usr/bin/env python3
"""Removes the embedded bitmap strikes (EBDT/EBLC/EBSC/BDF) from Wine's Tahoma so FreeType renders outlines.

Why: the OldEraMT2 client draws its UI text with its own FreeType code (EterLib FontManager, LCD rendering).
With Wine's tahoma.ttf, FreeType returns the embedded 1-bit bitmaps for the small UI sizes and the client
shows garbled slivers. Microsoft's Tahoma has no bitmap strikes. The outlines, metrics and names of the font
stay untouched. Wine's fonts are LGPL 2.1+ (modified copy; source = Wine 11.0 fonts/tahoma.sfd).
usage: strip-font-bitmaps.py IN.ttf OUT.ttf"""
import struct, sys

DROP = {b'EBDT', b'EBLC', b'EBSC', b'BDF '}


def checksum(data):
    data += b'\0' * (-len(data) % 4)
    return sum(struct.unpack('>%dI' % (len(data) // 4), data)) & 0xFFFFFFFF


def main(src, dst):
    b = open(src, 'rb').read()
    version, num = struct.unpack('>4sH', b[:6])
    assert version in (b'\0\1\0\0', b'true'), 'TrueType outlines expected'
    tables = []
    for i in range(num):
        tag, _, off, length = struct.unpack('>4sIII', b[12 + 16 * i:28 + 16 * i])
        if tag not in DROP:
            tables.append((tag, b[off:off + length]))
    tables.sort()
    n = len(tables)
    es = n.bit_length() - 1
    sr = (1 << es) * 16
    out = bytearray(struct.pack('>4sHHHH', version, n, sr, es, n * 16 - sr))
    offset = 12 + 16 * n
    body = bytearray()
    records = []
    for tag, data in tables:
        if tag == b'head':
            data = data[:8] + b'\0\0\0\0' + data[12:]          # checkSumAdjustment = 0 while summing
        records.append((tag, checksum(data), offset + len(body), len(data)))
        body += data + b'\0' * (-len(data) % 4)
    for rec in records:
        out += struct.pack('>4sIII', *rec)
    font = out + body
    head = next(r for r in records if r[0] == b'head')
    adj = (0xB1B0AFBA - checksum(bytes(font))) & 0xFFFFFFFF
    font[head[2] + 8:head[2] + 12] = struct.pack('>I', adj)
    open(dst, 'wb').write(font)
    print('%s: %d -> %d tables, dropped %s' % (dst, num, n, sorted(t.decode() for t in DROP)))


if __name__ == '__main__':
    main(sys.argv[1], sys.argv[2])