hf2 heightmap parser for python

hf2.py

# Copyright 2023 Kristupas Stumbrys

# This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

# This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

# See https://www.gnu.org/licenses/gpl-3.0.en.html


# spec
# http://www.bundysoft.com/docs/doku.php?id=l3dt:formats:specs:hf2

from struct import unpack


FILE_ID = b'HF2\x00'
VERSION = 0


def parse(bytes):
    fileId, version, width, height, tileSize, verticalPrecision, horizontalScale, extendedHeaderLength = unpack(
        '=4sHLLHffL', bytes[0:28])
    # Ignoring the extended header
    bytes = bytes[28 + extendedHeaderLength:]

    if fileId != FILE_ID:
        raise Exception(
            "Invalid fileId, excepted " + str(FILE_ID) + ", got " + str(fileId))

    if version != VERSION:
        raise Exception(
            "Invalid version, excepted " + str(VERSION) + ", got " + str(version))

    heights = [0] * (width * height)

    # Inner loop is x coord!
    for y in range(0, height, tileSize):
        for x in range(0, width, tileSize):
            # Parsing tile
            verticalScale, verticalOffset = unpack('=ff', bytes[0:8])
            bytes = bytes[8:]

            for l in range(0, min(tileSize, height - y)):
                # Parsing line
                byteDepth, startValue = unpack('=BL', bytes[0:5])
                bytes = bytes[5:]

                lineIndex = x + (y + l) * width
                heights[lineIndex] = startValue * \
                    verticalScale + verticalOffset
                lastValue = startValue

                for i in range(0, min(tileSize, width - x) - 1):
                    # Parsing cell
                    if byteDepth == 1:
                        offset = unpack('=b', bytes[0:1])[0]
                        bytes = bytes[1:]
                    elif byteDepth == 2:
                        offset = unpack('=h', bytes[0:2])[0]
                        bytes = bytes[2:]
                    elif byteDepth == 4:
                        offset = unpack('=l', bytes[0:4])[0]
                        bytes = bytes[4:]
                    else:
                        raise Exception(
                            "Unexpected byteDepth: " + str(byteDepth))

                    value = lastValue + offset
                    lastValue = value
                    heights[lineIndex + i + 1] = value * \
                        verticalScale + verticalOffset

    if len(bytes) != 0:
        raise Exception("Not all bytes were parsed in the hfz: " + str(bytes))

    return (width, height, heights)