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//! Decoding of GIF Images
//!
//! GIF (Graphics Interchange Format) is an image format that supports lossless compression.
//!
//! # Related Links
//! * <http://www.w3.org/Graphics/GIF/spec-gif89a.txt> - The GIF Specification
//!
extern crate gif;
extern crate num_rational;
use std::io::{Read, Write};
use std::clone::Clone;
pub use self::gif::{Frame, DisposalMethod};
use self::gif::{SetParameter, ColorOutput};
use image::{ImageError, ImageResult, DecodingResult, ImageDecoder};
use color::Rgba;
use color;
use animation::{Frame as Image_Frame, Frames as Image_Frames};
use buffer::{ImageBuffer, Pixel};
use num_rational::Ratio;
enum Either<T, U> {
Left(T),
Right(U)
}
/// GIF decoder
pub struct Decoder<R: Read> {
inner: Option<Either<gif::Decoder<R>, gif::Reader<R>>>
}
impl<R: Read> Decoder<R> {
/// Creates a new decoder that decodes the input steam ```r```
pub fn new(r: R) -> Decoder<R> {
let mut decoder = gif::Decoder::new(r);
decoder.set(ColorOutput::RGBA);
Decoder {
inner: Some(Either::Left(decoder))
}
}
// Converts the inner decoder to a reader
fn get_reader(&mut self) -> Result<&mut gif::Reader<R>, gif::DecodingError> {
let inner = self.inner.take().unwrap();
self.inner = Some(match inner {
Either::Left(decoder) => {
let reader = try!(decoder.read_info());
Either::Right(reader)
},
Either::Right(reader) => Either::Right(reader)
});
match self.inner {
Some(Either::Right(ref mut reader)) => Ok(reader),
_ => unreachable!()
}
}
}
impl<R: Read> ImageDecoder for Decoder<R> {
fn dimensions(&mut self) -> ImageResult<(u32, u32)> {
let reader = try!(self.get_reader());
Ok((u32::from(reader.width()), u32::from(reader.height())))
}
fn colortype(&mut self) -> ImageResult<color::ColorType> {
Ok(color::ColorType::RGBA(8))
}
fn row_len(&mut self) -> ImageResult<usize> {
let reader = try!(self.get_reader());
Ok(reader.line_length())
}
fn read_scanline(&mut self, buf: &mut [u8]) -> ImageResult<u32> {
let reader = try!(self.get_reader());
let len = reader.line_length();
try!(reader.fill_buffer(&mut buf[..len]));
Ok(len as u32)
}
fn read_image(&mut self) -> ImageResult<DecodingResult> {
let reader = try!(self.get_reader());
if try!(reader.next_frame_info()).is_some() {
let mut buf = vec![0; reader.buffer_size()];
try!(reader.read_into_buffer(&mut buf));
Ok(DecodingResult::U8(buf))
} else {
Err(ImageError::ImageEnd)
}
}
fn is_animated(&mut self) -> ImageResult<bool> {
Ok(true)
}
fn into_frames(mut self) -> ImageResult<Image_Frames> {
let reader = try!(self.get_reader());
let width = reader.width() as u32;
let height = reader.height() as u32;
// variable to hold all the image frames
let mut frames = Vec::new();
// set the background color to be either the bg_color defined in the gif
// or a transparent pixel.
let background_color_option = reader.bg_color();
let mut background_color = vec![0; 4];
let background_pixel = {
let global_palette = reader.global_palette();
match background_color_option {
Some(index) => {
// find the color by looking in the global palette
match global_palette {
// take the color from the palette that is at the index defined
// by background_color_option
Some(slice) => {
background_color.clone_from_slice(&slice[index .. (index+4)]);
Rgba::from_slice(&background_color)
},
// if there is no global palette, assign the background color to be
// transparent
None => Rgba::from_slice(&[0, 0, 0, 0]),
}
},
// return a transparent background color
None => Rgba::from_slice(&[0, 0, 0, 0]),
}
};
// create the background image to use later
let background_img = ImageBuffer::from_pixel(width, height, *background_pixel);
// the background image is the first non disposed frame
let mut non_disposed_frame = background_img.clone();
// define the variables used by each frame
let mut left: u32;
let mut top: u32;
let mut delay: Ratio<u16>;
let mut dispose: DisposalMethod;
// begin looping over each frame
loop {
if let Some(frame) = try!(reader.next_frame_info()) {
left = frame.left as u32;
top = frame.top as u32;
// frame.delay is in units of 10ms so frame.delay*10 is in ms
delay = Ratio::new(frame.delay*10, 1);
dispose = frame.dispose;
} else {
// no more frames, so end the loop here
break;
}
let mut vec = vec![0; reader.buffer_size()];
try!(reader.fill_buffer(&mut vec));
// create the image buffer from the raw frame
if let Some(mut image_buffer) = ImageBuffer::from_raw(width, height, vec) {
let previous_img_buffer = non_disposed_frame.clone();
// loop over all pixels, checking if any pixels from the non disposed
// frame need to be used
for (x, y, pixel) in image_buffer.enumerate_pixels_mut() {
let mut adjusted_pixel: &mut Rgba<u8> = pixel;
let previous_pixel: &Rgba<u8> = previous_img_buffer.get_pixel(x, y);
let pixel_alpha = adjusted_pixel.channels()[3];
// If a pixel is not visible then we show the non disposed frame pixel instead
if pixel_alpha == 0 {
adjusted_pixel.blend(previous_pixel);
}
}
let frame = Image_Frame::from_parts(image_buffer.clone(), left, top, delay);
frames.push(frame);
match dispose {
DisposalMethod::Any => {
// do nothing
// (completely replace this frame with the next)
},
DisposalMethod::Keep => {
// do not dispose
// (keep pixels from this frame)
non_disposed_frame = image_buffer;
},
DisposalMethod::Background => {
// restore to background color
// (background shows through transparent pixels in the next frame)
non_disposed_frame = background_img.clone();
},
DisposalMethod::Previous => {
// restore to previous
// (dispose frames leaving the last none disposal frame)
},
};
};
}
Ok(Image_Frames::new(frames))
}
}
/// GIF encoder.
pub struct Encoder<W: Write> {
w: W,
}
impl<W: Write> Encoder<W> {
/// Creates a new GIF encoder.
pub fn new(w: W) -> Encoder<W> {
Encoder {
w: w
}
}
/// Encodes a frame.
pub fn encode(self, frame: Frame) -> ImageResult<()> {
let mut encoder = try!(
gif::Encoder::new(self.w, frame.width, frame.height, &[])
);
encoder.write_frame(&frame).map_err(|err| err.into())
}
}
impl From<gif::DecodingError> for ImageError {
fn from(err: gif::DecodingError) -> ImageError {
use self::gif::DecodingError::*;
match err {
Format(desc) |
Internal(desc) => ImageError::FormatError(desc.into()),
Io(io_err) => ImageError::IoError(io_err),
}
}
}