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Data Types

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Miigon讨论 | 贡献2016年7月18日 (一) 21:57的版本 (translate)
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所有通过网络发送的数据均为大端序(big-endian,这意味着字节被从高位向低位发送。日常中大多数的计算机为小端序,所以可能需要在发送数据到网络之前将其转换为大端序。

Name Size (bytes) Encodes Notes
Boolean 1 false or true Value can be either true (0x01) or false (0x00)
Byte 1 -128 to 127 Signed 8-bit integer, two's complement
Unsigned Byte 1 0 to 255 Unsigned 8-bit integer
Short 2 -32768 to 32767 Signed 16-bit integer, two's complement
Unsigned Short 2 0 to 65535 Unsigned 16-bit integer
Int 4 -2147483648 to 2147483647 Signed 32-bit integer, two's complement
Long 8 -9223372036854775808 to 9223372036854775807 Signed 64-bit integer, two's complement
Float 4 Single-precision 32-bit IEEE 754 floating point
Double 8 Double-precision 64-bit IEEE 754 floating point
String ≥ 1
≤ 2147483652
A sequence of Unicode code points UTF-8 string prefixed with its size in bytes as a VarInt
Chat ≥ 1
≤ 2147483652
See Chat Encoded as a String
VarInt ≥ 1
≤ 5
-2147483648 to 2147483647 Protocol Buffer Varint, encoding a two's complement signed 32-bit integer
VarLong ≥ 1
≤ 10
-9223372036854775808 to 9223372036854775807 Protocol Buffer Varint, encoding a two's complement signed 64-bit integer
Chunk Varies A vertical chunk column See SMP Map Format#Data
Metadata Varies See Entities#Entity Metadata Format
Slot Varies See Slot Data
Object Data 4 or 10 See Object Data
NBT Tag Varies See NBT
Position 8 Integer/block position: x (-33554432 to 33554431), y (-2048 to 2047), z (-33554432 to 33554431) x as a 26-bit integer, followed by y as a 12-bit integer, followed by z as a 26-bit integer (all signed, two's complement). See also the section below.
Angle 1 Rotation angle in steps of 1/256 of a full turn Whether or not this is signed does not matter, since the resulting angles are the same.
UUID 16 A UUID The vanilla Minecraft server internally sends this as two longs.
this.writeLong(uuid.getMostSignificantBits());
this.writeLong(uuid.getLeastSignificantBits());
Optional X 0 or size of X A field of type X, or nothing Whether or not the field is present must be known from the context.
Array of X count times size of X Zero or more fields of type X The count must be known from the context.
Byte Array Varies Depends on context This is just a sequence of zero or more bytes, its meaning should be explained somewhere else, e.g. in the packet description. The length must also be known from the context.

位置

分成 3 部分的 64 个比特位

  • x: 26 MSBs
  • z: 26 LSBs
  • y: 12 bits between them

像这样编码:

((x & 0x3FFFFFF) << 38) | ((y & 0xFFF) << 26) | (z & 0x3FFFFFF)

像这样解码:

long val; // Encoded value
x = val >> 38;
y = (val >> 26) & 0xFFF
z = val << 38 >> 38

Note: 位移的细节是和编程语言相关的;以上代码若没有调整可能在 Java 中正确运行但在其他语言中无法正确运行????。

定点数据

有些域可能会被存储为 定点数(fixed point),即使用一定数量的比特位来存储小数的整数部分(小数点的左边),其余比特位表示小数部分 (小数点的右边)。浮点数 (float 和 double) 则相反,它将数字本身(底数)放在一个块里, 小数点的位置(指数)在其一旁存储。

实际上,虽然定点数的范围比浮点数小,但他们对于更高数值的精度更高。这使得他们成为在Minecraft中表示一个实体的全局坐标的理想选择,因为比起在一个方块(或一米)中精确的确定他们的位置而言,存储表示他们所在方块的整数部分显得更重要。

坐标通常被表示为一个 32 位的整型,低 5 位被用来存储小数部分,剩余的用来存储整数部分。

Java 缺乏对带小数部分的整型的直接支持,但你可以将他们表示为整型(integer)。如果要从一个 double 转换到这个整型表示,使用以下公式:

 abs_int = (int)double * 32;

逆向过程:

 double = (double)abs_int / 32;