结构包装和拆包不正确

Question

我正在尝试在GLTF中创建一个简单的立方体。我正在使用 Python 脚本将索引和顶点缓冲区写入二进制数据。这是我的代码;

import base64
import struct
indices = [
    0,  1,  2,  0,  2,  3,  # Front
    4,  5,  6,  4,  6,  7,  # Right
    8,  9,  10, 8,  10, 11, # Back
    12, 13, 14, 12, 14, 15, # Left
    16, 17, 18, 16, 18, 19, # Upper
    20, 21, 22, 20, 22, 23  # Bottom
]
faces = [
    [   # Front
        -1.0, -1.0, 1.0,
        1.0, -1.0, 1.0,
        1.0, 1.0, 1.0,
        -1.0, 1.0, 1.0
    ],
    [   # Right
        1.0, 1.0, 1.0,
        1.0, 1.0, -1.0,
        1.0, -1.0, -1.0,
        1.0, -1.0, 1.0
    ],
    [   # Back
        -1.0, -1.0, -1.0,
        1.0, -1.0, -1.0,
        1.0, 1.0, -1.0,
        -1.0, 1.0, -1.0
    ],
    [   # Left
        -1.0, -1.0, -1.0,
        -1.0, -1.0, 1.0,
        -1.0, 1.0, 1.0,
        -1.0, 1.0, -1.0
    ],
    [   # Upper
        1.0, 1.0, 1.0,
        -1.0, 1.0, 1.0,
        -1.0, 1.0, -1.0,
        1.0, 1.0, -1.0
    ],
    [   # Bottom
        -1.0, -1.0, -1.0,
        1.0, -1.0, -1.0,
        1.0, -1.0, 1.0,
        -1.0, -1.0, 1.0
    ]
]
length = 2 * len(indices) + 4 * len(faces) * len(faces[0])
buffer = bytearray(length)
offset = 0
# Write index array.
for index in indices:
    struct.pack_into('H', buffer, offset, index)
    offset = offset + 1
# Write vertex array.
for face in faces:
    for vertex in face:
        struct.pack_into('f', buffer, offset, vertex)
        offset = offset + 1
# Test
index_format = 'H' * 36
vertex_format = 'f' * 72
data_format = index_format + vertex_format
print(data_format)
print(struct.unpack(data_format, buffer))
# Write to base64.
b64 = base64.b64encode(buffer)
print(b64)

问题是，当我解压缩数据时，它给出了不知从何而来的奇怪值：

(256, 2, 770, 1284, 1030, 1798, 2312, 2058, 2826, 3340, 3086, 3854, 4368, 4114, 4882, 5396, 5142, 5910, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 5.831554006032442e-39, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0,
0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0)

我不知道我做错了什么。如果我使用与解压缩相同的格式打包数据，为什么这些值会有所不同？

Answer 1

当我在处理我的答案时，您已经发布了答案。但是，这里有一个变体：

• 紧凑(打包在 2 行代码中完成(
• 一般(完全依赖于指数和面结构(

code.py：

#!/usr/bin/env python3
import sys
import base64
import struct

def main():
    indices = [
        0,  1,  2,  0,  2,  3,  # Front
        4,  5,  6,  4,  6,  7,  # Right
        8,  9,  10, 8,  10, 11, # Back
        12, 13, 14, 12, 14, 15, # Left
        16, 17, 18, 16, 18, 19, # Upper
        20, 21, 22, 20, 22, 23  # Bottom
    ]
    faces = [
        [   # Front
            -1.0, -1.0, 1.0,
            1.0, -1.0, 1.0,
            1.0, 1.0, 1.0,
            -1.0, 1.0, 1.0
        ],
        [   # Right
            1.0, 1.0, 1.0,
            1.0, 1.0, -1.0,
            1.0, -1.0, -1.0,
            1.0, -1.0, 1.0
        ],
        [   # Back
            -1.0, -1.0, -1.0,
            1.0, -1.0, -1.0,
            1.0, 1.0, -1.0,
            -1.0, 1.0, -1.0
        ],
        [   # Left
            -1.0, -1.0, -1.0,
            -1.0, -1.0, 1.0,
            -1.0, 1.0, 1.0,
            -1.0, 1.0, -1.0
        ],
        [   # Upper
            1.0, 1.0, 1.0,
            -1.0, 1.0, 1.0,
            -1.0, 1.0, -1.0,
            1.0, 1.0, -1.0
        ],
        [   # Bottom
            -1.0, -1.0, -1.0,
            1.0, -1.0, -1.0,
            1.0, -1.0, 1.0,
            -1.0, -1.0, 1.0
        ]
    ]
    # @TODO - cfati: Relevant code is below (3 lines)
    format = "H" * len(indices) + "f" * sum((len(face) for face in faces))
    buf = struct.pack(format, *indices + [i for face in faces for i in face])
    buf_b64 = base64.b64encode(buf)
    print("Format: {:}".format(format))
    print("nBuffer unpacked: {:}".format(struct.unpack(format, buf)))
    print("nBuffer base64'ed: {:}".format(buf_b64))

if __name__ == "__main__":
    print("Python {:s} on {:s}n".format(sys.version, sys.platform))
    main()
    print("nDone.")

输出：

[cfati@CFATI-5510-0:e:WorkDevStackOverflowq056530761]> "e:WorkDevVEnvspy_064_03.07.03_test0Scriptspython.exe" code.py
Python 3.7.3 (v3.7.3:ef4ec6ed12, Mar 25 2019, 22:22:05) [MSC v.1916 64 bit (AMD64)] on win32
Format: HHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
Buffer unpacked: (0, 1, 2, 0, 2, 3, 4, 5, 6, 4, 6, 7, 8, 9, 10, 8, 10, 11, 12, 13, 14, 12, 14, 15, 16, 17, 18, 16, 18, 19, 20, 21, 22, 20, 22, 23, -1.0, -1.0, 1.0, 1.0, -1.0, 1.0, 1.0, 1.0, 1.0, -1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, -1.0, 1.0, -1.0, -1.0, 1.0, -1.0, 1.0, -1.0, -1.0, -1.0, 1.0, -1.0, -1.0, 1.0, 1.0, -1.0, -1.0, 1.0, -1.0, -1.0, -1.0, -1.0, -1.0, -1.0, 1.0, -1.0, 1.0, 1.0, -1.0, 1.0, -1.0, 1.0, 1.0, 1.0, -1.0, 1.0, 1.0, -1.0, 1.0, -1.0, 1.0, 1.0, -1.0, -1.0, -1.0, -1.0, 1.0, -1.0, -1.0, 1.0, -1.0, 1.0, -1.0, -1.0, 1.0)
Buffer base64'ed: b'AAABAAIAAAACAAMABAAFAAYABAAGAAcACAAJAAoACAAKAAsADAANAA4ADAAOAA8AEAARABIAEAASABMAFAAVABYAFAAWABcAAACAvwAAgL8AAIA/AACAPwAAgL8AAIA/AACAPwAAgD8AAIA/AACAvwAAgD8AAIA/AACAPwAAgD8AAIA/AACAPwAAgD8AAIC/AACAPwAAgL8AAIC/AACAPwAAgL8AAIA/AACAvwAAgL8AAIC/AACAPwAAgL8AAIC/AACAPwAAgD8AAIC/AACAvwAAgD8AAIC/AACAvwAAgL8AAIC/AACAvwAAgL8AAIA/AACAvwAAgD8AAIA/AACAvwAAgD8AAIC/AACAPwAAgD8AAIA/AACAvwAAgD8AAIA/AACAvwAAgD8AAIC/AACAPwAAgD8AAIC/AACAvwAAgL8AAIC/AACAPwAAgL8AAIC/AACAPwAAgL8AAIA/AACAvwAAgL8AAIA/'
Done.

Answer 2

我想出了解决方案。问题是我只将offset增加了 1。写unsigned short时，我应该把它增加2。而写float的时候，我应该增加4。

正确的代码：

# Write index array.
for index in indices:
    struct.pack_into('H', buffer, offset, index)
    offset = offset + 2
# Write vertex array.
for face in faces:
    for vertex in face:
        struct.pack_into('f', buffer, offset, vertex)
        offset = offset + 4