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
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
use super::header::{Header, ImageType, ALPHA_BIT_MASK, SCREEN_ORIGIN_BIT_MASK};
use crate::{
    color::{ColorType, ExtendedColorType},
    error::{
        ImageError, ImageResult, LimitError, LimitErrorKind, UnsupportedError, UnsupportedErrorKind,
    },
    image::{ImageDecoder, ImageFormat, ImageReadBuffer},
};
use byteorder::ReadBytesExt;
use std::{
    io::{self, Read, Seek},
    mem,
};

struct ColorMap {
    /// sizes in bytes
    start_offset: usize,
    entry_size: usize,
    bytes: Vec<u8>,
}

impl ColorMap {
    pub(crate) fn from_reader(
        r: &mut dyn Read,
        start_offset: u16,
        num_entries: u16,
        bits_per_entry: u8,
    ) -> ImageResult<ColorMap> {
        let bytes_per_entry = (bits_per_entry as usize + 7) / 8;

        let mut bytes = vec![0; bytes_per_entry * num_entries as usize];
        r.read_exact(&mut bytes)?;

        Ok(ColorMap {
            entry_size: bytes_per_entry,
            start_offset: start_offset as usize,
            bytes,
        })
    }

    /// Get one entry from the color map
    pub(crate) fn get(&self, index: usize) -> Option<&[u8]> {
        let entry = self.start_offset + self.entry_size * index;
        self.bytes.get(entry..entry + self.entry_size)
    }
}

/// The representation of a TGA decoder
pub struct TgaDecoder<R> {
    r: R,

    width: usize,
    height: usize,
    bytes_per_pixel: usize,
    has_loaded_metadata: bool,

    image_type: ImageType,
    color_type: ColorType,
    original_color_type: Option<ExtendedColorType>,

    header: Header,
    color_map: Option<ColorMap>,

    // Used in read_scanline
    line_read: Option<usize>,
    line_remain_buff: Vec<u8>,
}

impl<R: Read + Seek> TgaDecoder<R> {
    /// Create a new decoder that decodes from the stream `r`
    pub fn new(r: R) -> ImageResult<TgaDecoder<R>> {
        let mut decoder = TgaDecoder {
            r,

            width: 0,
            height: 0,
            bytes_per_pixel: 0,
            has_loaded_metadata: false,

            image_type: ImageType::Unknown,
            color_type: ColorType::L8,
            original_color_type: None,

            header: Header::default(),
            color_map: None,

            line_read: None,
            line_remain_buff: Vec::new(),
        };
        decoder.read_metadata()?;
        Ok(decoder)
    }

    fn read_header(&mut self) -> ImageResult<()> {
        self.header = Header::from_reader(&mut self.r)?;
        self.image_type = ImageType::new(self.header.image_type);
        self.width = self.header.image_width as usize;
        self.height = self.header.image_height as usize;
        self.bytes_per_pixel = (self.header.pixel_depth as usize + 7) / 8;
        Ok(())
    }

    fn read_metadata(&mut self) -> ImageResult<()> {
        if !self.has_loaded_metadata {
            self.read_header()?;
            self.read_image_id()?;
            self.read_color_map()?;
            self.read_color_information()?;
            self.has_loaded_metadata = true;
        }
        Ok(())
    }

    /// Loads the color information for the decoder
    ///
    /// To keep things simple, we won't handle bit depths that aren't divisible
    /// by 8 and are larger than 32.
    fn read_color_information(&mut self) -> ImageResult<()> {
        if self.header.pixel_depth % 8 != 0 || self.header.pixel_depth > 32 {
            // Bit depth must be divisible by 8, and must be less than or equal
            // to 32.
            return Err(ImageError::Unsupported(
                UnsupportedError::from_format_and_kind(
                    ImageFormat::Tga.into(),
                    UnsupportedErrorKind::Color(ExtendedColorType::Unknown(
                        self.header.pixel_depth,
                    )),
                ),
            ));
        }

        let num_alpha_bits = self.header.image_desc & ALPHA_BIT_MASK;

        let other_channel_bits = if self.header.map_type != 0 {
            self.header.map_entry_size
        } else {
            if num_alpha_bits > self.header.pixel_depth {
                return Err(ImageError::Unsupported(
                    UnsupportedError::from_format_and_kind(
                        ImageFormat::Tga.into(),
                        UnsupportedErrorKind::Color(ExtendedColorType::Unknown(
                            self.header.pixel_depth,
                        )),
                    ),
                ));
            }

            self.header.pixel_depth - num_alpha_bits
        };
        let color = self.image_type.is_color();

        match (num_alpha_bits, other_channel_bits, color) {
            // really, the encoding is BGR and BGRA, this is fixed
            // up with `TgaDecoder::reverse_encoding`.
            (0, 32, true) => self.color_type = ColorType::Rgba8,
            (8, 24, true) => self.color_type = ColorType::Rgba8,
            (0, 24, true) => self.color_type = ColorType::Rgb8,
            (8, 8, false) => self.color_type = ColorType::La8,
            (0, 8, false) => self.color_type = ColorType::L8,
            (8, 0, false) => {
                // alpha-only image is treated as L8
                self.color_type = ColorType::L8;
                self.original_color_type = Some(ExtendedColorType::A8);
            }
            _ => {
                return Err(ImageError::Unsupported(
                    UnsupportedError::from_format_and_kind(
                        ImageFormat::Tga.into(),
                        UnsupportedErrorKind::Color(ExtendedColorType::Unknown(
                            self.header.pixel_depth,
                        )),
                    ),
                ))
            }
        }
        Ok(())
    }

    /// Read the image id field
    ///
    /// We're not interested in this field, so this function skips it if it
    /// is present
    fn read_image_id(&mut self) -> ImageResult<()> {
        self.r
            .seek(io::SeekFrom::Current(i64::from(self.header.id_length)))?;
        Ok(())
    }

    fn read_color_map(&mut self) -> ImageResult<()> {
        if self.header.map_type == 1 {
            // FIXME: we could reverse the map entries, which avoids having to reverse all pixels
            // in the final output individually.
            self.color_map = Some(ColorMap::from_reader(
                &mut self.r,
                self.header.map_origin,
                self.header.map_length,
                self.header.map_entry_size,
            )?);
        }
        Ok(())
    }

    /// Expands indices into its mapped color
    fn expand_color_map(&self, pixel_data: &[u8]) -> io::Result<Vec<u8>> {
        #[inline]
        fn bytes_to_index(bytes: &[u8]) -> usize {
            let mut result = 0usize;
            for byte in bytes.iter() {
                result = result << 8 | *byte as usize;
            }
            result
        }

        let bytes_per_entry = (self.header.map_entry_size as usize + 7) / 8;
        let mut result = Vec::with_capacity(self.width * self.height * bytes_per_entry);

        if self.bytes_per_pixel == 0 {
            return Err(io::ErrorKind::Other.into());
        }

        let color_map = self
            .color_map
            .as_ref()
            .ok_or_else(|| io::Error::from(io::ErrorKind::Other))?;

        for chunk in pixel_data.chunks(self.bytes_per_pixel) {
            let index = bytes_to_index(chunk);
            if let Some(color) = color_map.get(index) {
                result.extend_from_slice(color);
            } else {
                return Err(io::ErrorKind::Other.into());
            }
        }

        Ok(result)
    }

    /// Reads a run length encoded data for given number of bytes
    fn read_encoded_data(&mut self, num_bytes: usize) -> io::Result<Vec<u8>> {
        let mut pixel_data = Vec::with_capacity(num_bytes);
        let mut repeat_buf = Vec::with_capacity(self.bytes_per_pixel);

        while pixel_data.len() < num_bytes {
            let run_packet = self.r.read_u8()?;
            // If the highest bit in `run_packet` is set, then we repeat pixels
            //
            // Note: the TGA format adds 1 to both counts because having a count
            // of 0 would be pointless.
            if (run_packet & 0x80) != 0 {
                // high bit set, so we will repeat the data
                let repeat_count = ((run_packet & !0x80) + 1) as usize;
                self.r
                    .by_ref()
                    .take(self.bytes_per_pixel as u64)
                    .read_to_end(&mut repeat_buf)?;

                // get the repeating pixels from the bytes of the pixel stored in `repeat_buf`
                let data = repeat_buf
                    .iter()
                    .cycle()
                    .take(repeat_count * self.bytes_per_pixel);
                pixel_data.extend(data);
                repeat_buf.clear();
            } else {
                // not set, so `run_packet+1` is the number of non-encoded pixels
                let num_raw_bytes = (run_packet + 1) as usize * self.bytes_per_pixel;
                self.r
                    .by_ref()
                    .take(num_raw_bytes as u64)
                    .read_to_end(&mut pixel_data)?;
            }
        }

        if pixel_data.len() > num_bytes {
            // FIXME: the last packet contained more data than we asked for!
            // This is at least a warning. We truncate the data since some methods rely on the
            // length to be accurate in the success case.
            pixel_data.truncate(num_bytes);
        }

        Ok(pixel_data)
    }

    /// Reads a run length encoded packet
    fn read_all_encoded_data(&mut self) -> ImageResult<Vec<u8>> {
        let num_bytes = self.width * self.height * self.bytes_per_pixel;

        Ok(self.read_encoded_data(num_bytes)?)
    }

    /// Reads a run length encoded line
    fn read_encoded_line(&mut self) -> io::Result<Vec<u8>> {
        let line_num_bytes = self.width * self.bytes_per_pixel;
        let remain_len = self.line_remain_buff.len();

        if remain_len >= line_num_bytes {
            // `Vec::split_to` if std had it
            let bytes = {
                let bytes_after = self.line_remain_buff.split_off(line_num_bytes);
                mem::replace(&mut self.line_remain_buff, bytes_after)
            };

            return Ok(bytes);
        }

        let num_bytes = line_num_bytes - remain_len;

        let line_data = self.read_encoded_data(num_bytes)?;

        let mut pixel_data = Vec::with_capacity(line_num_bytes);
        pixel_data.append(&mut self.line_remain_buff);
        pixel_data.extend_from_slice(&line_data[..num_bytes]);

        // put the remain data to line_remain_buff.
        // expects `self.line_remain_buff` to be empty from
        // the above `pixel_data.append` call
        debug_assert!(self.line_remain_buff.is_empty());
        self.line_remain_buff
            .extend_from_slice(&line_data[num_bytes..]);

        Ok(pixel_data)
    }

    /// Reverse from BGR encoding to RGB encoding
    ///
    /// TGA files are stored in the BGRA encoding. This function swaps
    /// the blue and red bytes in the `pixels` array.
    fn reverse_encoding_in_output(&mut self, pixels: &mut [u8]) {
        // We only need to reverse the encoding of color images
        match self.color_type {
            ColorType::Rgb8 | ColorType::Rgba8 => {
                for chunk in pixels.chunks_mut(self.color_type.bytes_per_pixel().into()) {
                    chunk.swap(0, 2);
                }
            }
            _ => {}
        }
    }

    /// Flip the image vertically depending on the screen origin bit
    ///
    /// The bit in position 5 of the image descriptor byte is the screen origin bit.
    /// If it's 1, the origin is in the top left corner.
    /// If it's 0, the origin is in the bottom left corner.
    /// This function checks the bit, and if it's 0, flips the image vertically.
    fn flip_vertically(&mut self, pixels: &mut [u8]) {
        if self.is_flipped_vertically() {
            if self.height == 0 {
                return;
            }

            let num_bytes = pixels.len();

            let width_bytes = num_bytes / self.height;

            // Flip the image vertically.
            for vertical_index in 0..(self.height / 2) {
                let vertical_target = (self.height - vertical_index) * width_bytes - width_bytes;

                for horizontal_index in 0..width_bytes {
                    let source = vertical_index * width_bytes + horizontal_index;
                    let target = vertical_target + horizontal_index;

                    pixels.swap(target, source);
                }
            }
        }
    }

    /// Check whether the image is vertically flipped
    ///
    /// The bit in position 5 of the image descriptor byte is the screen origin bit.
    /// If it's 1, the origin is in the top left corner.
    /// If it's 0, the origin is in the bottom left corner.
    /// This function checks the bit, and if it's 0, flips the image vertically.
    fn is_flipped_vertically(&self) -> bool {
        let screen_origin_bit = SCREEN_ORIGIN_BIT_MASK & self.header.image_desc != 0;
        !screen_origin_bit
    }

    fn read_scanline(&mut self, buf: &mut [u8]) -> io::Result<usize> {
        if let Some(line_read) = self.line_read {
            if line_read == self.height {
                return Ok(0);
            }
        }

        // read the pixels from the data region
        let mut pixel_data = if self.image_type.is_encoded() {
            self.read_encoded_line()?
        } else {
            let num_raw_bytes = self.width * self.bytes_per_pixel;
            let mut buf = vec![0; num_raw_bytes];
            self.r.by_ref().read_exact(&mut buf)?;
            buf
        };

        // expand the indices using the color map if necessary
        if self.image_type.is_color_mapped() {
            pixel_data = self.expand_color_map(&pixel_data)?;
        }
        self.reverse_encoding_in_output(&mut pixel_data);

        // copy to the output buffer
        buf[..pixel_data.len()].copy_from_slice(&pixel_data);

        self.line_read = Some(self.line_read.unwrap_or(0) + 1);

        Ok(pixel_data.len())
    }
}

impl<'a, R: 'a + Read + Seek> ImageDecoder<'a> for TgaDecoder<R> {
    type Reader = TGAReader<R>;

    fn dimensions(&self) -> (u32, u32) {
        (self.width as u32, self.height as u32)
    }

    fn color_type(&self) -> ColorType {
        self.color_type
    }

    fn original_color_type(&self) -> ExtendedColorType {
        self.original_color_type
            .unwrap_or_else(|| self.color_type().into())
    }

    fn scanline_bytes(&self) -> u64 {
        // This cannot overflow because TGA has a maximum width of u16::MAX_VALUE and
        // `bytes_per_pixel` is a u8.
        u64::from(self.color_type.bytes_per_pixel()) * self.width as u64
    }

    fn into_reader(self) -> ImageResult<Self::Reader> {
        Ok(TGAReader {
            buffer: ImageReadBuffer::new(
                #[allow(deprecated)]
                self.scanline_bytes(),
                self.total_bytes(),
            ),
            decoder: self,
        })
    }

    fn read_image(mut self, buf: &mut [u8]) -> ImageResult<()> {
        assert_eq!(u64::try_from(buf.len()), Ok(self.total_bytes()));

        // In indexed images, we might need more bytes than pixels to read them. That's nonsensical
        // to encode but we'll not want to crash.
        let mut fallback_buf = vec![];
        // read the pixels from the data region
        let rawbuf = if self.image_type.is_encoded() {
            let pixel_data = self.read_all_encoded_data()?;
            if self.bytes_per_pixel <= usize::from(self.color_type.bytes_per_pixel()) {
                buf[..pixel_data.len()].copy_from_slice(&pixel_data);
                &buf[..pixel_data.len()]
            } else {
                fallback_buf = pixel_data;
                &fallback_buf[..]
            }
        } else {
            let num_raw_bytes = self.width * self.height * self.bytes_per_pixel;
            if self.bytes_per_pixel <= usize::from(self.color_type.bytes_per_pixel()) {
                self.r.by_ref().read_exact(&mut buf[..num_raw_bytes])?;
                &buf[..num_raw_bytes]
            } else {
                fallback_buf.resize(num_raw_bytes, 0u8);
                self.r
                    .by_ref()
                    .read_exact(&mut fallback_buf[..num_raw_bytes])?;
                &fallback_buf[..num_raw_bytes]
            }
        };

        // expand the indices using the color map if necessary
        if self.image_type.is_color_mapped() {
            let pixel_data = self.expand_color_map(rawbuf)?;
            // not enough data to fill the buffer, or would overflow the buffer
            if pixel_data.len() != buf.len() {
                return Err(ImageError::Limits(LimitError::from_kind(
                    LimitErrorKind::DimensionError,
                )));
            }
            buf.copy_from_slice(&pixel_data);
        }

        self.reverse_encoding_in_output(buf);

        self.flip_vertically(buf);

        Ok(())
    }
}

pub struct TGAReader<R> {
    buffer: ImageReadBuffer,
    decoder: TgaDecoder<R>,
}
impl<R: Read + Seek> Read for TGAReader<R> {
    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
        let decoder = &mut self.decoder;
        self.buffer.read(buf, |buf| decoder.read_scanline(buf))
    }
}