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80 lines
3.0 KiB
Python
80 lines
3.0 KiB
Python
from collections import namedtuple
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def load_directory(data_bytes, offset, num_entries):
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tile_entries = {}
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leaves = {}
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for i in range(offset, offset + num_entries * 17, 17):
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z = int.from_bytes(data_bytes[i : i + 1], byteorder="little")
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x = int.from_bytes(data_bytes[i + 1 : i + 4], byteorder="little")
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y = int.from_bytes(data_bytes[i + 4 : i + 7], byteorder="little")
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tile_off = int.from_bytes(data_bytes[i + 7 : i + 13], byteorder="little")
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tile_len = int.from_bytes(data_bytes[i + 13 : i + 17], byteorder="little")
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if z & 0b10000000:
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leaves[(z & 0b01111111, x, y)] = (tile_off, tile_len)
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else:
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tile_entries[(z, x, y)] = (tile_off, tile_len)
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return tile_entries, leaves
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Header = namedtuple("Header", ["version", "metadata", "root_dir", "leaves"])
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class Reader:
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def __init__(self, get_bytes):
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self.get_bytes = get_bytes
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self._header = None
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def header(self):
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if self._header:
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return self._header
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else:
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header_bytes = self.get_bytes(0, 512000)
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assert int.from_bytes(header_bytes[0:2], byteorder="little") == 0x4D50
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version = int.from_bytes(header_bytes[2:4], byteorder="little")
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metadata_len = int.from_bytes(header_bytes[4:8], byteorder="little")
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metadata = json.loads(header_bytes[10 : 10 + metadata_len])
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num_entries = int.from_bytes(header_bytes[8:10], byteorder="little")
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root_dir, leaves = load_directory(
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header_bytes, 10 + metadata_len, num_entries
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)
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self._header = Header(version, metadata, root_dir, leaves)
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return self._header
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def _leaf_level(self):
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h = self.header()
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return next(iter(h.leaves))[0]
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def get(self, z, x, y):
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h = self.header()
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val = h.root_dir.get((z, x, y))
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if val:
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return self.get_bytes(val[0], val[1])
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else:
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if len(self.header().leaves) > 0:
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level_diff = z - self._leaf_level()
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if level_diff < 0:
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return None
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leaf = (
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self._leaf_level(),
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x // (1 << level_diff),
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y // (1 << level_diff),
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)
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val = h.leaves.get(leaf)
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if val:
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dir_bytes = self.get_bytes(val[0], val[1])
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directory, _ = load_directory(dir_bytes, 0, val[1] // 17)
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val = directory.get((z, x, y))
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if val:
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return self.get_bytes(val[0], val[1])
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def tiles(self):
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h = self.header()
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for k, v in h.root_dir.items():
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yield (k, self.get_bytes(v[0], v[1]))
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for val in set(h.leaves.values()):
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dir_bytes = self.get_bytes(val[0], val[1])
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leaf_dir, _ = load_directory(dir_bytes, 0, val[1] // 17)
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for k, v in leaf_dir.items():
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yield (k, self.get_bytes(v[0], v[1]))
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