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use crate::version::DEFAULT_MESH_VERSION;
/// Output buffer for writing Draco bitstream data.
///
/// `EncoderBuffer` accumulates encoded bytes and supports both byte-aligned
/// writes and packed bit-level encoding for entropy-coded sections. Encoders
/// write into it; after encoding, [`data`](EncoderBuffer::data) returns the
/// finished bitstream as a byte slice ready to hand to a `DecoderBuffer` or
/// write to a file.
pub struct EncoderBuffer {
buffer: Vec<u8>,
bit_encoder_active: bool,
bit_start_pos: usize,
current_bit_offset: usize,
version_major: u8,
version_minor: u8,
encode_bit_sequence_size: bool,
}
impl Default for EncoderBuffer {
fn default() -> Self {
Self {
buffer: Vec::new(),
bit_encoder_active: false,
bit_start_pos: 0,
current_bit_offset: 0,
// Default to the latest mesh version so standalone encode/decode
// (e.g. encode_symbols/decode_symbols) agrees with DecoderBuffer::new().
version_major: DEFAULT_MESH_VERSION.0,
version_minor: DEFAULT_MESH_VERSION.1,
encode_bit_sequence_size: false,
}
}
}
impl EncoderBuffer {
/// Creates an empty encoder buffer.
pub fn new() -> Self {
Self::default()
}
/// Sets the target Draco bitstream version.
pub fn set_version(&mut self, major: u8, minor: u8) {
self.version_major = major;
self.version_minor = minor;
}
/// Returns the target major bitstream version.
pub fn version_major(&self) -> u8 {
self.version_major
}
/// Returns the target minor bitstream version.
pub fn version_minor(&self) -> u8 {
self.version_minor
}
/// Returns the packed `0xMMmm` target bitstream version for ordered comparisons.
pub fn bitstream_version(&self) -> u16 {
crate::version::bitstream_version(self.version_major, self.version_minor)
}
/// Clears all encoded bytes and resets active bit encoding state.
pub fn clear(&mut self) {
self.buffer.clear();
self.bit_encoder_active = false;
self.current_bit_offset = 0;
}
/// Resizes the underlying byte buffer.
pub fn resize(&mut self, nbytes: usize) {
self.buffer.resize(nbytes, 0);
}
/// Starts writing a packed bit sequence.
pub fn start_bit_encoding(&mut self, required_bits: usize, encode_size: bool) -> bool {
if self.bit_encoder_active {
return false;
}
self.encode_bit_sequence_size = encode_size;
if encode_size {
// Reserve 8 bytes for the size (will be replaced by varint or fixed 8 bytes later)
for _ in 0..8 {
self.buffer.push(0);
}
}
let required_bytes = required_bits.div_ceil(8);
self.bit_start_pos = self.buffer.len();
self.buffer.resize(self.bit_start_pos + required_bytes, 0);
self.bit_encoder_active = true;
self.current_bit_offset = 0;
true
}
/// Finishes the active packed bit sequence.
pub fn end_bit_encoding(&mut self) {
if !self.bit_encoder_active {
return;
}
self.bit_encoder_active = false;
if self.encode_bit_sequence_size {
let encoded_bits = self.current_bit_offset;
let encoded_bytes = encoded_bits.div_ceil(8);
let bitstream_version = self.bitstream_version();
let mut var_size_buffer = Vec::new();
if bitstream_version >= 0x0202 {
// Encode size as varint
let mut v = encoded_bytes as u64;
loop {
let mut byte = (v & 0x7F) as u8;
v >>= 7;
if v != 0 {
byte |= 0x80;
var_size_buffer.push(byte);
} else {
var_size_buffer.push(byte);
break;
}
}
} else {
// Encode size as fixed 8 bytes
var_size_buffer.extend_from_slice(&(encoded_bytes as u64).to_le_bytes());
}
let size_len = var_size_buffer.len();
let reserved_pos = self.bit_start_pos - 8;
// Move encoded data to its final position
let src_pos = self.bit_start_pos;
let dst_pos = reserved_pos + size_len;
if dst_pos != src_pos {
self.buffer
.copy_within(src_pos..src_pos + encoded_bytes, dst_pos);
}
// Write the size
self.buffer[reserved_pos..reserved_pos + size_len].copy_from_slice(&var_size_buffer);
// Resize buffer to final size
self.buffer.resize(dst_pos + encoded_bytes, 0);
} else {
// Just resize to actual encoded bytes
let encoded_bytes = self.current_bit_offset.div_ceil(8);
self.buffer.resize(self.bit_start_pos + encoded_bytes, 0);
}
}
/// Writes the least significant `nbits` bits of a 32-bit value.
pub fn encode_least_significant_bits32(&mut self, nbits: u32, value: u32) -> bool {
if !self.bit_encoder_active {
return false;
}
if nbits == 0 {
return true;
}
// Pack bits efficiently into the underlying byte buffer.
// Bits are written LSB-first, matching Draco's EncoderBuffer.
let mut remaining_bits = nbits;
let mut v = value;
while remaining_bits > 0 {
let total_bit_offset = self.current_bit_offset;
let byte_offset = self.bit_start_pos + (total_bit_offset / 8);
let bit_shift = (total_bit_offset % 8) as u32;
let available = 8u32 - bit_shift;
let take = remaining_bits.min(available);
let mask = (1u32 << take) - 1;
let bits = v & mask;
self.buffer[byte_offset] |= (bits as u8) << bit_shift;
v >>= take;
remaining_bits -= take;
self.current_bit_offset += take as usize;
}
true
}
/// Appends a plain-old-data value in native memory representation.
pub fn encode<T: bytemuck::NoUninit>(&mut self, data: T) -> bool {
if self.bit_encoder_active {
return false;
}
let slice = bytemuck::bytes_of(&data);
self.buffer.extend_from_slice(slice);
true
}
/// Appends raw bytes.
pub fn encode_data(&mut self, data: &[u8]) -> bool {
if self.bit_encoder_active {
return false;
}
self.buffer.extend_from_slice(data);
true
}
/// Appends one byte.
pub fn encode_u8(&mut self, val: u8) {
self.buffer.push(val);
}
/// Appends a little-endian `u16`.
pub fn encode_u16(&mut self, val: u16) {
self.buffer.extend_from_slice(&val.to_le_bytes());
}
/// Appends a little-endian `u32`.
pub fn encode_u32(&mut self, val: u32) {
self.buffer.extend_from_slice(&val.to_le_bytes());
}
/// Appends a little-endian `u64`.
pub fn encode_u64(&mut self, val: u64) {
self.buffer.extend_from_slice(&val.to_le_bytes());
}
/// Appends an unsigned LEB128-style Draco varint.
pub fn encode_varint<T: Into<u64>>(&mut self, val: T) {
let mut v = val.into();
loop {
let mut byte = (v & 0x7F) as u8;
v >>= 7;
if v != 0 {
byte |= 0x80;
self.buffer.push(byte);
} else {
self.buffer.push(byte);
break;
}
}
}
/// Draco-compatible signed varint (ConvertSignedIntToSymbol + unsigned varint).
pub fn encode_varint_signed_i32(&mut self, val: i32) {
let symbol: u32 = if val >= 0 {
(val as u32) << 1
} else {
let mapped = (-(val + 1)) as u32;
(mapped << 1) | 1
};
self.encode_varint(symbol as u64);
}
/// Returns the encoded byte slice.
pub fn data(&self) -> &[u8] {
&self.buffer
}
/// Returns the encoded byte length.
pub fn size(&self) -> usize {
self.buffer.len()
}
}