imagesize/formats/
tga.rs

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1use std::io::{BufRead, Seek, SeekFrom};
2
3use crate::{util::*, ImageResult, ImageSize};
4
5pub fn size<R: BufRead + Seek>(reader: &mut R) -> ImageResult<ImageSize> {
6    reader.seek(SeekFrom::Start(12))?;
7
8    let width = read_u16(reader, &Endian::Little)? as usize;
9    let height = read_u16(reader, &Endian::Little)? as usize;
10
11    Ok(ImageSize { width, height })
12}
13
14pub fn matches<R: BufRead + Seek>(header: &[u8], reader: &mut R) -> bool {
15    // Do a naive check first to filter out any obviously non-TGA files
16    let colormap_type = header[1];
17    let image_type = header[2];
18
19    // Check the image type (byte 2) to be one of the uncompressed or RLE compressed types
20    // Note: I've seen mention of types 0, 32, and 33 but have no example files so have omitted them.
21    if image_type != 1
22        && image_type != 2
23        && image_type != 3
24        && image_type != 9
25        && image_type != 10
26        && image_type != 11
27    {
28        return false;
29    }
30
31    // Check that the colormap type (byte 1) is either 0 (no colormap) or 1 (colormap present)
32    // Technically 2-127 is reserved and 128-255 are usable by devs, but for simplicity we ignore them
33    if colormap_type >= 2 {
34        return false;
35    }
36
37    is_tga(reader, image_type, colormap_type).unwrap_or(false)
38}
39
40fn is_tga<R: BufRead + Seek>(reader: &mut R, image_type: u8, colormap_type: u8) -> ImageResult<bool> {
41    // Attempt to go to footer section. This also doubles as a size check since
42    // if there aren't 18 bytes available it will return an error.
43    reader.seek(SeekFrom::End(-18))?;
44
45    // Look for Version 2 TGA footer signature as it's the only concrete data to verify it's a TGA
46    let mut signature = [0; 18];
47    reader.read_exact(&mut signature)?;
48
49    // If signature is found then we should be confident it's a TGA
50    //
51    // We do not reset the seek here because size methods should
52    // be seeking themselves as a first step anyway.
53    if &signature == b"TRUEVISION-XFILE.\0" {
54        return Ok(true);
55    }
56
57    // Now we're into heuristic territory. 
58    // With no footer I don't believe there is a 100% way to verify whether given bytes 
59    // are a TGA or not. To get around this we add a few corroborating byte checks and
60    // if they make up a valid TGA configuration we assume that it's a TGA.
61
62    // If image type is color mapped, then color map type must be set to 1
63    if (image_type == 1 || image_type == 9) && colormap_type != 1 {
64        return Ok(false);
65    }
66
67    // Start reading the header information
68    reader.seek(SeekFrom::Start(3))?;
69
70    let colormap_offset = read_u32(reader, &Endian::Little)?;
71    let colormap_size = read_u8(reader)?;
72
73    // If there is no color map then assume that origin, length, and entry size must be 0
74    if colormap_type == 0 {
75        if colormap_offset != 0 {
76            return Ok(false);
77        }
78
79        if colormap_size != 0 {
80            return Ok(false);
81        }
82    }
83
84    // Assume color map sizes must be a multiple of 8
85    if colormap_type == 1 && 
86       (colormap_size != 0 && 
87        colormap_size != 8 && 
88        colormap_size != 16 && 
89        colormap_size != 24 && 
90        colormap_size != 32)
91    {
92        return Ok(false);
93    }
94
95    reader.seek(SeekFrom::Start(16))?;
96    let pixel_size = read_u8(reader)?;
97    let descriptor = read_u8(reader)?;
98    let alpha_bits = descriptor & 0x0F;
99
100    // Reserved bit, must be set to 0
101    if descriptor & 0x10 != 0 {
102        return Ok(false);
103    }
104
105    // Assume pixel size must be a multiple of 8
106    if pixel_size != 8 && pixel_size != 16 && pixel_size != 24 && pixel_size != 32 {
107        return Ok(false);
108    }
109
110    // Verify that the alpha bits value makes sense given pixel size
111    //
112    // 8 and 24 bits have no alpha
113    if (pixel_size == 8 || pixel_size == 24) && alpha_bits != 0 {
114        return Ok(false);
115    }
116
117    // 16 bits can either have 0 or 1 bits of alpha
118    if pixel_size == 16 && alpha_bits >= 2 {
119        return Ok(false);
120    }
121
122    // 32 bits must have 8 bits of alpha, although I've seen one with 0?
123    if pixel_size == 32 && (alpha_bits != 8 && alpha_bits != 0) {
124        return Ok(false);
125    }
126
127    Ok(true)
128}
imagesize/formats/tga.rs

imagesize/formats/
tga.rs
