draco-core 1.0.2

Pure Rust core encoder and decoder for Draco geometry compression
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140

//! Folded 32-bit integer coder.
//!
//! Encodes/decodes a 32-bit integer as a sequence of bits, each modeled by its
//! own binary rANS context ("folding"), so high-entropy and low-entropy bit
//! positions are coded separately. Used for KD-tree point-cloud attribute
//! values. Port of Draco's `folded_integer_coding`/`FoldedBit32` coders.

#[cfg(feature = "decoder")]
use crate::decoder_buffer::DecoderBuffer;
#[cfg(feature = "encoder")]
use crate::encoder_buffer::EncoderBuffer;
#[cfg(feature = "decoder")]
use crate::rans_bit_decoder::RAnsBitDecoder;
#[cfg(feature = "encoder")]
use crate::rans_bit_encoder::RAnsBitEncoder;

#[cfg(feature = "encoder")]
pub struct FoldedBit32Encoder {
    folded_number_encoders: Vec<RAnsBitEncoder>,
    bit_encoder: RAnsBitEncoder,
}

#[cfg(feature = "encoder")]
impl Default for FoldedBit32Encoder {
    fn default() -> Self {
        Self {
            folded_number_encoders: (0..32).map(|_| RAnsBitEncoder::new()).collect(),
            bit_encoder: RAnsBitEncoder::new(),
        }
    }
}

#[cfg(feature = "encoder")]
impl FoldedBit32Encoder {
    pub fn new() -> Self {
        Self::default()
    }

    pub fn start_encoding(&mut self) {
        for enc in &mut self.folded_number_encoders {
            enc.start_encoding();
        }
        self.bit_encoder.start_encoding();
    }

    pub fn encode_bit(&mut self, bit: bool) {
        self.bit_encoder.encode_bit(bit);
    }

    pub fn encode_least_significant_bits32(&mut self, nbits: u32, value: u32) {
        assert!(nbits > 0 && nbits <= 32);
        let mut selector = 1u32 << (nbits - 1);
        for i in 0..nbits {
            let bit = (value & selector) != 0;
            self.folded_number_encoders[i as usize].encode_bit(bit);
            selector >>= 1;
        }
    }

    pub fn end_encoding(&mut self, target_buffer: &mut EncoderBuffer) {
        for enc in &mut self.folded_number_encoders {
            enc.end_encoding(target_buffer);
        }
        self.bit_encoder.end_encoding(target_buffer);
    }
}

#[cfg(feature = "decoder")]
pub struct FoldedBit32Decoder<'a> {
    folded_number_decoders: Vec<RAnsBitDecoder<'a>>,
    bit_decoder: RAnsBitDecoder<'a>,
}

#[cfg(feature = "decoder")]
impl<'a> Default for FoldedBit32Decoder<'a> {
    fn default() -> Self {
        Self {
            folded_number_decoders: (0..32).map(|_| RAnsBitDecoder::new()).collect(),
            bit_decoder: RAnsBitDecoder::new(),
        }
    }
}

#[cfg(feature = "decoder")]
impl<'a> FoldedBit32Decoder<'a> {
    pub fn new() -> Self {
        Self::default()
    }

    pub fn start_decoding(&mut self, source_buffer: &mut DecoderBuffer<'a>) -> bool {
        for dec in &mut self.folded_number_decoders {
            if !dec.start_decoding(source_buffer) {
                return false;
            }
        }
        self.bit_decoder.start_decoding(source_buffer)
    }

    pub fn decode_next_bit(&mut self) -> bool {
        self.bit_decoder.decode_next_bit()
    }

    pub fn decode_least_significant_bits32(&mut self, nbits: u32, value: &mut u32) -> bool {
        if nbits == 0 || nbits > 32 {
            return false;
        }
        let mut result = 0u32;
        for i in 0..nbits {
            let Some(decoder) = self.folded_number_decoders.get_mut(i as usize) else {
                return false;
            };
            let bit = decoder.decode_next_bit();
            result = (result << 1) + (bit as u32);
        }
        *value = result;
        true
    }

    pub fn end_decoding(&mut self) {
        self.bit_decoder.end_decoding();
        for dec in &mut self.folded_number_decoders {
            dec.end_decoding();
        }
    }
}

#[cfg(all(test, feature = "decoder"))]
mod tests {
    use super::*;

    #[test]
    fn decode_least_significant_bits32_rejects_invalid_bit_counts() {
        let mut decoder = FoldedBit32Decoder::new();
        let mut value = 123;

        assert!(!decoder.decode_least_significant_bits32(0, &mut value));
        assert!(!decoder.decode_least_significant_bits32(33, &mut value));
        assert_eq!(value, 123);
    }
}