Struct png::encoder::ChunkWriter

struct ChunkWriter<'a, W: Write> {
    writer: ChunkOutput<'a, W>,
    buffer: Vec<u8>,
    index: usize,
    curr_chunk: ChunkType,
}

This writer is used between the actual writer and the ZlibEncoder and has the job of packaging the compressed data into a PNG chunk, based on the image metadata

Currently the way it works is that the specified buffer will hold one chunk at the time and buffer the incoming data until flush is called or the maximum chunk size is reached.

The maximum chunk is the smallest between the selected buffer size and u32::MAX >> 1 (0x7fffffff or 2147483647 dec)

When a chunk has to be flushed the length (that is now known) and the CRC will be written at the correct locations in the chunk.

Fields

writer: ChunkOutput<'a, W>

buffer: Vec<u8>

index: usize

keeps track of where the last byte was written

curr_chunk: ChunkType

Implementations

impl<'a, W: Write> ChunkWriter<'a, W>

fn new(writer: ChunkOutput<'a, W>, buf_len: usize) -> ChunkWriter<'a, W>

fn next_frame_info(&self) -> (usize, usize)

Returns the size of each scanline for the next frame paired with the size of the whole frame

This is used by the StreamWriter to know when the scanline ends so it can filter compress it and also to know when to start the next one

fn write_header(&mut self) -> Result<(), EncodingError>

NOTE: this bypasses the internal buffer so the flush method should be called before this in the case there is some data left in the buffer when this is called, it will panic

fn set_fctl(&mut self, f: FrameControl)

Set the FrameControl for the following frame

It will ignore the sequence_number of the parameter as it is updated internally.

fn flush_inner(&mut self) -> Result<()>

Flushes the current chunk

Trait Implementations

impl<W: Write> Drop for ChunkWriter<'_, W>

fn drop(&mut self)

Executes the destructor for this type.

impl<'a, W: Write> Write for ChunkWriter<'a, W>

fn write(&mut self, data: &[u8]) -> Result<usize>

Write a buffer into this writer, returning how many bytes were written.

fn flush(&mut self) -> Result<()>

Flush this output stream, ensuring that all intermediately buffered contents reach their destination.

fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> Result<usize, Error>

Like write, except that it writes from a slice of buffers.

fn is_write_vectored(&self) -> bool

🔬This is a nightly-only experimental API. (can_vector)

Determines if this Writer has an efficient write_vectored implementation.

fn write_all(&mut self, buf: &[u8]) -> Result<(), Error>

Attempts to write an entire buffer into this writer.

fn write_all_vectored(&mut self, bufs: &mut [IoSlice<'_>]) -> Result<(), Error>

🔬This is a nightly-only experimental API. (write_all_vectored)

Attempts to write multiple buffers into this writer.

fn write_fmt(&mut self, fmt: Arguments<'_>) -> Result<(), Error>

Writes a formatted string into this writer, returning any error encountered.

fn by_ref(&mut self) -> &mut Selfwhere Self: Sized,

Creates a “by reference” adapter for this instance of Write.