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use std::io::{self, Read};
use byteorder::{ReadBytesExt, LittleEndian};
use num::FromPrimitive;
use num::rational::Ratio;
use imageops::overlay;
use color;
use animation::Frame;
use image::{ImageError, ImageResult, DecodingResult, ImageDecoder};
use buffer::{ImageBuffer, GrayImage, RgbaImage};
use utils::lzw;
use utils::bitstream::{LsbReader};
#[derive(PartialEq)]
enum State {
Start,
HaveHeader,
HaveLSD,
}
pub struct GIFDecoder<R: Read> {
r: R,
state: State,
width: u16,
height: u16,
global_table: Vec<(u8, u8, u8)>,
global_background_index: Option<u8>,
delay: u16,
local_transparent_index: Option<u8>,
}
impl<R: Read> GIFDecoder<R> {
pub fn new(r: R) -> GIFDecoder<R> {
GIFDecoder {
r: r,
state: State::Start,
width: 0,
height: 0,
global_table: Vec::new(),
global_background_index: None,
delay: 0,
local_transparent_index: None,
}
}
fn read_header(&mut self) -> ImageResult<()> {
if self.state == State::Start {
let mut signature = [0; 3];
if try!(self.r.read(&mut signature)) != 3 {
return Err(ImageError::ImageEnd);
}
let mut version = [0; 3];
if try!(self.r.read(&mut version)) != 3 {
return Err(ImageError::ImageEnd);
}
if signature != b"GIF"[..] {
Err(ImageError::FormatError("GIF signature not found.".to_string()))
} else if version != b"87a"[..] && version != b"89a"[..] {
Err(ImageError::UnsupportedError(
format!("GIF version {:?} is not supported.", version)
))
} else {
self.state = State::HaveHeader;
Ok(())
}
} else { Ok(()) }
}
fn read_logical_screen_descriptor(&mut self) -> ImageResult<()> {
try!(self.read_header());
if self.state == State::HaveHeader {
self.width = try!(self.r.read_u16::<LittleEndian>());
self.height = try!(self.r.read_u16::<LittleEndian>());
let fields = try!(self.r.read_u8());
let global_table = fields & 0x80 != 0;
let entries = if global_table {
1 << ((fields & 0b111) + 1) as usize
} else {
0usize
};
let b = try!(self.r.read_u8());
if global_table {
self.global_table.reserve_exact(entries);
self.global_background_index = Some(b);
}
let _aspect_ratio = try!(self.r.read_u8());
let mut buf = Vec::with_capacity(3 * entries);
try!(self.r.by_ref().take(3 * entries as u64).read_to_end(&mut buf));
for rgb in buf.chunks(3) {
self.global_table.push((rgb[0], rgb[1], rgb[2]));
}
self.state = State::HaveLSD;
Ok(())
} else { Ok(()) }
}
fn read_extension(&mut self) -> ImageResult<()> {
use super::Extension::{Text, Control, Comment, Application};
match FromPrimitive::from_u8(try!(self.r.read_u8())) {
Some(Text) => try!(self.skip_extension()),
Some(Control) => try!(self.read_control_extension()),
Some(Comment) => try!(self.skip_extension()),
Some(Application) => try!(self.skip_extension()),
None => try!(self.skip_extension())
}
Ok(())
}
fn read_control_extension(&mut self) -> ImageResult<()> {
let size = try!(self.r.read_u8());
if size != 4 {
return Err(ImageError::FormatError(
"Malformed graphics control extension.".to_string()
))
}
let fields = try!(self.r.read_u8());
self.delay = try!(self.r.read_u16::<LittleEndian>());
let trans = try!(self.r.read_u8());
if fields & 1 != 0 {
self.local_transparent_index = Some(trans);
}
let size = try!(self.r.read_u8());
if size != 0 {
return Err(ImageError::FormatError(
"Malformed graphics control extension.".to_string()
))
}
Ok(())
}
fn skip_extension(&mut self) -> ImageResult<()> {
let mut size = try!(self.r.read_u8());
while size != 0 {
for _ in (0..size) {
let _ = try!(self.r.read_u8());
}
size = try!(self.r.read_u8());
}
Ok(())
}
fn read_data(&mut self) -> ImageResult<Vec<u8>> {
let mut size = try!(self.r.read_u8()) as usize;
let mut data = Vec::with_capacity(size);
while size != 0 {
try!(self.r.by_ref().take(size as u64).read_to_end(&mut data));
size = try!(self.r.read_u8()) as usize;
}
Ok(data)
}
#[allow(unused_variables)]
fn read_frame(&mut self) -> ImageResult<Frame> {
let image_left = try!(self.r.read_u16::<LittleEndian>());
let image_top = try!(self.r.read_u16::<LittleEndian>());
let image_width = try!(self.r.read_u16::<LittleEndian>());
let image_height = try!(self.r.read_u16::<LittleEndian>());
let fields = try!(self.r.read_u8());
let local_table = (fields & 0b1000_0000) != 0;
let interlace = (fields & 0b0100_0000) != 0;
let table_size = fields & 0b0000_0111;
if interlace {
return Err(ImageError::UnsupportedError(
"Interlaced images are not supported.".to_string()
))
}
let local_table = if local_table {
let entries = 1 << (table_size + 1) as usize;
let mut table = Vec::with_capacity(entries * 3);
let mut buf = Vec::with_capacity(3 * entries);
try!(self.r.by_ref().take(3 * entries as u64).read_to_end(&mut buf));
for rgb in buf.chunks(3) {
table.push((rgb[0], rgb[1], rgb[2]));
}
Some(table)
} else {
None
};
let code_size = try!(self.r.read_u8());
let data = try!(self.read_data());
let mut indices = Vec::with_capacity(
image_width as usize
* image_height as usize
);
try!(lzw::decode(
LsbReader::new(io::Cursor::new(data)),
&mut indices,
code_size
));
let table = if let Some(ref table) = local_table {
table
} else {
&self.global_table
};
let image: Option<GrayImage> = ImageBuffer::from_vec(
image_width as u32,
image_height as u32,
indices
);
if let Some(image) = image {
let image = image.expand_palette(table, self.local_transparent_index);
Ok(Frame::from_parts(
image,
image_left as u32,
image_top as u32,
Ratio::new(self.delay, 100)
))
} else {
Err(ImageError::FormatError(
"Image data has not the expected size.".to_string()
))
}
}
fn next_frame(&mut self) -> ImageResult<Option<Frame>> {
use super::Block::{Image, Extension, Trailer};
try!(self.read_logical_screen_descriptor());
loop {
match FromPrimitive::from_u8(try!(self.r.read_u8())) {
Some(Extension) => try!(self.read_extension()),
Some(Image) => return self.read_frame().map(|v| Some(v)),
Some(Trailer) => return Ok(None),
None => return Err(ImageError::UnsupportedError(
"Unknown block encountered".to_string()
))
}
}
}
}
impl<R: Read> ImageDecoder for GIFDecoder<R> {
fn dimensions(&mut self) -> ImageResult<(u32, u32)> {
let _ = try!(self.read_logical_screen_descriptor());
Ok((self.width as u32, self.height as u32))
}
fn colortype(&mut self) -> ImageResult<color::ColorType> {
let _ = try!(self.read_logical_screen_descriptor());
Ok(color::ColorType::RGBA(8))
}
fn row_len(&mut self) -> ImageResult<usize> {
let _ = try!(self.read_logical_screen_descriptor());
Ok(3 * self.width as usize)
}
fn read_scanline(&mut self, _: &mut [u8]) -> ImageResult<u32> {
unimplemented!()
}
fn read_image(&mut self) -> ImageResult<DecodingResult> {
let (width, height) = try!(self.dimensions());
let background = if let Some(idx) = self.global_background_index {
let (r, g, b) = self.global_table[idx as usize];
color::Rgba([r, g, b, 255])
} else {
color::Rgba([0, 0, 0, 255])
};
let mut canvas: RgbaImage = ImageBuffer::from_pixel(width, height, background);
let frame = try!(self.next_frame());
match frame {
Some(frame) => {
let left = frame.left();
let top = frame.top();
let buffer = frame.into_buffer();
overlay(&mut canvas, &buffer, left, top);
while let Some(frame) = try!(self.next_frame()) {
if frame.delay() == Ratio::new(0, 100) {
let left = frame.left();
let top = frame.top();
let buffer = frame.into_buffer();
overlay(&mut canvas, &buffer, left, top);
} else {
break
}
}
Ok(DecodingResult::U8(canvas.into_raw()))
},
None => Err(ImageError::ImageEnd)
}
}
}