ai_imagesize/container/
pkm.rs

1use no_std_io::io::{BufRead, Seek, SeekFrom};
2
3use crate::{
4    util::{read_u16, Endian},
5    ImageResult, ImageSize,
6};
7
8/// Compression formats for PKM containers (ETC/EAC family)
9///
10/// PKM (PowerVR Texture Compression) format is used to store various ETC and EAC
11/// compressed textures. This enum identifies the specific compression variant.
12#[derive(Clone, Copy, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
13pub enum PkmCompression {
14    /// ETC1 RGB (original format)
15    Etc1,
16    /// ETC2 RGB (enhanced)
17    Etc2,
18    /// ETC2 with 1-bit punch-through alpha
19    Etc2A1,
20    /// ETC2 with 8-bit alpha channel
21    Etc2A8,
22    /// EAC single channel (R11)
23    EacR,
24    /// EAC two channel (RG11)
25    EacRg,
26    /// EAC single channel signed (R11_SIGNED)
27    EacRSigned,
28    /// EAC two channel signed (RG11_SIGNED)
29    EacRgSigned,
30    /// Other/Unknown PKM format
31    Unknown,
32}
33
34pub fn size<R: BufRead + Seek>(reader: &mut R) -> ImageResult<ImageSize> {
35    // ETC/EAC files are typically in PKM format
36    // PKM header structure:
37    // Magic: "PKM " (4 bytes)
38    // Version: "10" or "20" (2 bytes)
39    // Data type: 2 bytes (big-endian)
40    // Extended width: 2 bytes (big-endian)
41    // Extended height: 2 bytes (big-endian)
42    // Original width: 2 bytes (big-endian)
43    // Original height: 2 bytes (big-endian)
44
45    reader.seek(SeekFrom::Start(8))?; // Skip magic + version + data type
46    let _extended_width = read_u16(reader, &Endian::Big)?;
47    let _extended_height = read_u16(reader, &Endian::Big)?;
48    let width = read_u16(reader, &Endian::Big)? as usize;
49    let height = read_u16(reader, &Endian::Big)? as usize;
50
51    Ok(ImageSize { width, height })
52}
53
54pub fn matches(header: &[u8]) -> bool {
55    // PKM format magic number followed by version
56    if header.len() >= 6 {
57        return header.starts_with(b"PKM ")
58            && (header[4..6] == [b'1', b'0'] || header[4..6] == [b'2', b'0']);
59    }
60    false
61}
62
63pub fn matches_eac(header: &[u8]) -> bool {
64    // PKM format with EAC-specific data types
65    if header.len() >= 8
66        && header.starts_with(b"PKM ")
67        && (header[4..6] == [b'1', b'0'] || header[4..6] == [b'2', b'0'])
68    {
69        // Check data type for EAC formats
70        let data_type = u16::from_be_bytes([header[6], header[7]]);
71        return matches!(data_type, 0x1608..=0x160B);
72    }
73    false
74}
75
76pub fn detect_compression<R: BufRead + Seek>(reader: &mut R) -> ImageResult<PkmCompression> {
77    // Read the data type from PKM header to determine compression format
78    reader.seek(SeekFrom::Start(6))?; // Skip magic and version
79    let data_type = read_u16(reader, &Endian::Big)?;
80
81    let compression = match data_type {
82        // ETC1 formats
83        0x0000 => PkmCompression::Etc1, // ETC1_RGB_NO_MIPMAPS
84
85        // ETC2 formats
86        0x0001 => PkmCompression::Etc2, // ETC2PACKAGE_RGB_NO_MIPMAPS
87        0x0002 => PkmCompression::Etc2A1, // ETC2PACKAGE_RGBA1_NO_MIPMAPS (alternative)
88        0x0003 => PkmCompression::Etc2A8, // ETC2PACKAGE_RGBA_NO_MIPMAPS_OLD
89        0x0004 => PkmCompression::Etc2A1, // ETC2PACKAGE_RGBA1_NO_MIPMAPS (generated format)
90        0x0005 => PkmCompression::Etc2A8, // ETC2PACKAGE_RGBA_NO_MIPMAPS (generated format)
91
92        // Standard EAC formats
93        0x1608 => PkmCompression::EacRgSigned, // EAC_RG11_SIGNED_FORMAT
94        0x1609 => PkmCompression::EacRSigned,  // EAC_R11_SIGNED_FORMAT
95        0x160A => PkmCompression::EacR,        // EAC_R11_UNSIGNED_FORMAT
96        0x160B => PkmCompression::EacRg,       // EAC_RG11_UNSIGNED_FORMAT
97
98        _ => PkmCompression::Unknown,
99    };
100
101    Ok(compression)
102}
ai_imagesize/container/pkm.rs

ai_imagesize/container/
pkm.rs
