Crate metaverse_environment

Expand description

§Metaverse Environment

Environment library for open metaverse clients!

Provides handling for environment data sent from an open metaverse server. Will handle compression and decompression for heightmap files, and handling LayerData packets sent from the server.

§Packet spec

The LayerData Packet is laid out like this

LayerData
Packet Header	id:11	reliable: true	zerocoded: false	frequency: low

§Body Header

BodyHeader
Type	1 byte	u8	The type of the patch. Land, Water, Wind and Cloud.
Length	4 bytes	u16	The length of the packet’s patch data. For initializing a buffer.
Stride	1 byte	u8	The length of the data for each patch.
Patch Size	1 byte	u8	The size of the patches. Should always be 16.
Type	1 byte	u8	A redundant type value.
Content	variable bytes (read to end)	PatchData	Compressed patch data

The body header is followed by a byte array the length of the header’s length field, containing several individual patches.

§Patch Spec

Patch data
Quantized World Bits	1 byte	u8
DC Offset	4 bytes	f32
Range	2 bytes	u16
Patch IDs	10 or 4 bytes
Compressed Layer Data	vriable bytes (read to end)

For Patch IDs, If the region is extended, the first 5 bits of the 10 bit string are used for the x, and the next 5 represent the y. If the region is not extended, the first 2 bytes represent the x, and the next 2 represent the y. Stored in big-endian format.

§Patch Spec

§Bit packing information

Throughout this crate, occasionally bit values in the data are packed in a way that does not align them to a byte. This can be confusing, and cause for frustrating debugging.

For example:

Patch ids is used for determining the xy position of the patch. This can be either 10 bits, or 32 bits, depending on if it is an extended patch or not. The binary is read into a buffer, with the first half of the bytes being used as the x value, and the second half of the bytes being used as the y value.

However, the binary is laid out in big-endian format, which makes this very difficult to see. you might have raw data that looks like this after removing the headers from the packet

Bytes:     0    0    0   164  65   1    0    8   96 ...
           |    |    |    |   |    |    |    |    |
           |    |    |    |   |    |    |    └────└─ [8, 96] patch ID bytes
           |    |    |    |   |    └────└─ [1,0] range (2 bytes)
           |    └────└────└───└─[0, 0, 164, 65] f32 DC offset (4 bytes)
           └─[0] quantized_world_bits (1 byte)

Read as u8s, the values are

8	96
00001000	01100000

To handle 10 bytes, you read the whole of the first value, and the first two bits of the second.

00001000	01

Because it is big-endian, you have to move the two bits to the beginning of the data and then parse as a u32.

01	00001000

The resulting XY values come out to

01000	01000
x: 8	y: 8

This crate is in development!

This crate is not ready for public use! Most method are missing, and it is very unpolished.

Modules§

cloud: TODO: unimplemented
constants: This module contains constants used for decompression
error: error definitions
generate_triangles: This module handles generating the triangles required for generating the GLTF files.
land: Contains information and handling for land patches
layer_handler: This module handles parsing and decoding LayerData packets
water: TODO: unimplemented
wind: TODO: unimplemented