horntail 0.4.2

maplestory resource file unpack lib
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
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179

// source code take from
// https://github.com/image-rs/image/blob/main/src/codecs/dxt.rs
//!  Decoding of DXT (S3TC) compression
//!
//!  DXT is an image format that supports lossy compression
//!
//!  # Related Links
//!  * <https://www.khronos.org/registry/OpenGL/extensions/EXT/EXT_texture_compression_s3tc.txt> - Description of the DXT compression OpenGL extensions.
//!
//!  Note: this module only implements bare DXT encoding/decoding, it does not parse formats that can contain DXT files like .dds

/**
 * Actual encoding/decoding logic below.
 */
type Rgb = [u8; 3];

/// decodes a 5-bit R, 6-bit G, 5-bit B 16-bit packed color value into 8-bit RGB
/// mapping is done so min/max range values are preserved. So for 5-bit
/// values 0x00 -> 0x00 and 0x1F -> 0xFF
fn enc565_decode(value: u16) -> Rgb {
    let red = (value >> 11) & 0x1F;
    let green = (value >> 5) & 0x3F;
    let blue = (value) & 0x1F;
    [
        (red * 0xFF / 0x1F) as u8,
        (green * 0xFF / 0x3F) as u8,
        (blue * 0xFF / 0x1F) as u8,
    ]
}

/*
 * Functions for decoding DXT compression
 */

/// Constructs the DXT5 alpha lookup table from the two alpha entries
/// if alpha0 > alpha1, constructs a table of [a0, a1, 6 linearly interpolated values from a0 to a1]
/// if alpha0 <= alpha1, constructs a table of [a0, a1, 4 linearly interpolated values from a0 to a1, 0, 0xFF]
fn alpha_table_dxt5(alpha0: u8, alpha1: u8) -> [u8; 8] {
    let mut table = [alpha0, alpha1, 0, 0, 0, 0, 0, 0xFF];
    if alpha0 > alpha1 {
        for i in 2..8u16 {
            table[i as usize] =
                (((8 - i) * u16::from(alpha0) + (i - 1) * u16::from(alpha1)) / 7) as u8;
        }
    } else {
        for i in 2..6u16 {
            table[i as usize] =
                (((6 - i) * u16::from(alpha0) + (i - 1) * u16::from(alpha1)) / 5) as u8;
        }
    }
    table
}

/// decodes an 8-byte dxt color block into the RGB channels of a 16xRGB or 16xRGBA block.
/// source should have a length of 8, dest a length of 48 (RGB) or 64 (RGBA)
fn decode_dxt_colors(source: &[u8], dest: &mut [u8], is_dxt1: bool) {
    // sanity checks, also enable the compiler to elide all following bound checks
    assert!(source.len() == 8 && (dest.len() == 48 || dest.len() == 64));
    // calculate pitch to store RGB values in dest (3 for RGB, 4 for RGBA)
    let pitch = dest.len() / 16;

    // extract color data
    let color0 = u16::from(source[0]) | (u16::from(source[1]) << 8);
    let color1 = u16::from(source[2]) | (u16::from(source[3]) << 8);
    let color_table = u32::from(source[4])
        | (u32::from(source[5]) << 8)
        | (u32::from(source[6]) << 16)
        | (u32::from(source[7]) << 24);
    // let color_table = source[4..8].iter().rev().fold(0, |t, &b| (t << 8) | b as u32);

    // decode the colors to rgb format
    let mut colors = [[0; 3]; 4];
    colors[0] = enc565_decode(color0);
    colors[1] = enc565_decode(color1);

    // determine color interpolation method
    if color0 > color1 || !is_dxt1 {
        // linearly interpolate the other two color table entries
        for i in 0..3 {
            colors[2][i] = ((u16::from(colors[0][i]) * 2 + u16::from(colors[1][i]) + 1) / 3) as u8;
            colors[3][i] = ((u16::from(colors[0][i]) + u16::from(colors[1][i]) * 2 + 1) / 3) as u8;
        }
    } else {
        // linearly interpolate one other entry, keep the other at 0
        for i in 0..3 {
            colors[2][i] = (u16::from(colors[0][i]) + u16::from(colors[1][i])).div_ceil(2) as u8;
        }
    }

    // serialize the result. Every color is determined by looking up
    // two bits in color_table which identify which color to actually pick from the 4 possible colors
    for i in 0..16 {
        dest[i * pitch..i * pitch + 3]
            .copy_from_slice(&colors[(color_table >> (i * 2)) as usize & 3]);
    }
}

/// Decodes a 16-byte bock of dxt5 data to a 16xRGBA block
fn decode_dxt5_block(source: &[u8], dest: &mut [u8]) {
    assert!(source.len() == 16 && dest.len() == 64);

    // extract alpha index table (stored as little endian 64-bit value)
    let alpha_table = source[2..8]
        .iter()
        .rev()
        .fold(0, |t, &b| (t << 8) | u64::from(b));

    // alpha level decode
    let alphas = alpha_table_dxt5(source[0], source[1]);

    // serialize alpha
    for i in 0..16 {
        dest[i * 4 + 3] = alphas[(alpha_table >> (i * 3)) as usize & 7];
    }

    // handle colors
    decode_dxt_colors(&source[8..16], dest, false);
}

/// Decodes a 16-byte bock of dxt3 data to a 16xRGBA block
fn decode_dxt3_block(source: &[u8], dest: &mut [u8]) {
    assert!(source.len() == 16 && dest.len() == 64);

    // extract alpha index table (stored as little endian 64-bit value)
    let alpha_table = source[0..8]
        .iter()
        .rev()
        .fold(0, |t, &b| (t << 8) | u64::from(b));

    // serialize alpha (stored as 4-bit values)
    for i in 0..16 {
        dest[i * 4 + 3] = ((alpha_table >> (i * 4)) as u8 & 0xF) * 0x11;
    }

    // handle colors
    decode_dxt_colors(&source[8..16], dest, false);
}

/// Decode a row of DXT3 data to four rows of RGBA data.
/// `source.len()` should be a multiple of 16, otherwise this panics.
pub(crate) fn decode_dxt3_row(source: &[u8], dest: &mut [u8]) {
    assert!(source.len() % 16 == 0);
    let block_count = source.len() / 16;
    assert!(dest.len() >= block_count * 64);

    // contains the 16 decoded pixels per block
    let mut decoded_block = [0u8; 64];

    for (x, encoded_block) in source.chunks(16).enumerate() {
        decode_dxt3_block(encoded_block, &mut decoded_block);

        // copy the values from the decoded block to linewise RGB layout
        for line in 0..4 {
            let offset = (block_count * line + x) * 16;
            dest[offset..offset + 16].copy_from_slice(&decoded_block[line * 16..(line + 1) * 16]);
        }
    }
}

/// Decode a row of DXT5 data to four rows of RGBA data.
/// `source.len()` should be a multiple of 16, otherwise this panics.
pub(crate) fn decode_dxt5_row(source: &[u8], dest: &mut [u8]) {
    assert!(source.len() % 16 == 0);
    let block_count = source.len() / 16;
    assert!(dest.len() >= block_count * 64);

    // contains the 16 decoded pixels per block
    let mut decoded_block = [0u8; 64];

    for (x, encoded_block) in source.chunks(16).enumerate() {
        decode_dxt5_block(encoded_block, &mut decoded_block);

        // copy the values from the decoded block to linewise RGB layout
        for line in 0..4 {
            let offset = (block_count * line + x) * 16;
            dest[offset..offset + 16].copy_from_slice(&decoded_block[line * 16..(line + 1) * 16]);
        }
    }
}