Struct Reader 

pub struct Reader<R: BufRead + Seek> {
    decoder: ReadDecoder<R>,
    bpp: BytesPerPixel,
    subframe: SubframeInfo,
    remaining_frames: u32,
    unfiltering_buffer: UnfilteringBuffer,
    transform: Transformations,
    transform_fn: Option<Box<dyn Fn(&[u8], &mut [u8], &Info<'_>) + Send + Sync>>,
    scratch_buffer: Vec<u8>,
    finished: bool,
}

PNG reader (mostly high-level interface)

Provides a high level that iterates over lines or whole images.

Fields

decoder: ReadDecoder<R>

bpp: BytesPerPixel

subframe: SubframeInfo

remaining_frames: u32

How many frames remain to be decoded. Decremented after each IDAT or fdAT sequence.

unfiltering_buffer: UnfilteringBuffer

Buffer with not-yet-unfilter-ed image rows

transform: Transformations

Output transformations

transform_fn: Option<Box<dyn Fn(&[u8], &mut [u8], &Info<'_>) + Send + Sync>>

Function that can transform decompressed, unfiltered rows into final output. See the transform.rs module for more details.

scratch_buffer: Vec<u8>

This buffer is only used so that next_row and next_interlaced_row can return reference to a byte slice. In a future version of this library, this buffer will be removed and next_row and next_interlaced_row will write directly into a user provided output buffer.

finished: bool

Whether ImageEnd was already reached by fn finish.

Implementations

impl<R: BufRead + Seek> Reader<R>

pub fn next_frame_info(&mut self) -> Result<&FrameControl, DecodingError>

Advances to the start of the next animation frame and returns a reference to the FrameControl info that describes it. Skips and discards the image data of the previous frame if necessary.

Returns a ParameterError when there are no more animation frames. To avoid this the caller can check if Info::animation_control exists and consult AnimationControl::num_frames.

fn read_until_image_data(&mut self) -> Result<(), DecodingError>

Reads all meta data until the next frame data starts. Requires IHDR before the IDAT and fcTL before fdAT.

pub fn info(&self) -> &Info<'static>

Get information on the image.

The structure will change as new frames of an animated image are decoded.

pub fn next_frame( &mut self, buf: &mut [u8], ) -> Result<OutputInfo, DecodingError>

Decodes the next frame into buf.

Note that this decodes raw subframes that need to be mixed according to blend-op and dispose-op by the caller.

The caller must always provide a buffer large enough to hold a complete frame (the APNG specification restricts subframes to the dimensions given in the image header). The region that has been written be checked afterwards by calling Reader::info after a successful call and inspecting the frame_control data. This requirement may be lifted in a later version of png.

Output lines will be written in row-major, packed matrix with width and height of the read frame (or subframe), all samples are in big endian byte order where this matters.

fn mark_subframe_as_consumed_and_flushed(&mut self)

fn finish_decoding(&mut self) -> Result<(), DecodingError>

Advance over the rest of data for this (sub-)frame. Called after decoding the last row of a frame.

pub fn next_row(&mut self) -> Result<Option<Row<'_>>, DecodingError>

Returns the next processed row of the image (discarding InterlaceInfo).

See also Reader::read_row, which reads into a caller-provided buffer.

pub fn next_interlaced_row( &mut self, ) -> Result<Option<InterlacedRow<'_>>, DecodingError>

Returns the next processed row of the image.

See also Reader::read_row, which reads into a caller-provided buffer.

pub fn read_row( &mut self, output_buffer: &mut [u8], ) -> Result<Option<InterlaceInfo>, DecodingError>

Reads the next row of the image into the provided output_buffer. Ok(None) will be returned if the current image frame has no more rows.

output_buffer needs to be long enough to accommodate Reader::output_line_size for Info::width (initial interlaced rows may need less than that).

See also Reader::next_row and Reader::next_interlaced_row, which read into a Reader-owned buffer.

fn output_line_size_for_interlace_info( &self, interlace: &InterlaceInfo, ) -> usize

pub fn finish(&mut self) -> Result<(), DecodingError>

Read the rest of the image and chunks and finish up, including text chunks or others This will discard the rest of the image if the image is not read already with Reader::next_frame, Reader::next_row or Reader::next_interlaced_row

fn next_interlaced_row_impl( &mut self, rowlen: usize, output_buffer: &mut [u8], ) -> Result<(), DecodingError>

Fetch the next interlaced row and filter it according to our own transformations.

pub fn output_color_type(&self) -> (ColorType, BitDepth)

Returns the color type and the number of bits per sample of the data returned by Reader::next_row and Reader::next_frame.

pub fn output_buffer_size(&self) -> Option<usize>

Return the number of bytes required to hold a deinterlaced image frame that is decoded using the given input transformations.

Returns None if the output buffer does not fit into the memory space of the machine, otherwise returns the byte length in Some. The length is smaller than isize::MAX.

pub(crate) fn unguarded_output_line_size(&self, width: u32) -> usize

Returns the number of bytes required to hold a deinterlaced row.

pub fn output_line_size(&self, width: u32) -> Option<usize>

Returns the number of bytes required to hold a deinterlaced row.

Returns None if the output buffer does not fit into the memory space of the machine, otherwise returns the byte length in Some. The length is smaller than isize::MAX.

fn next_raw_interlaced_row( &mut self, rowlen: usize, ) -> Result<(), DecodingError>

Unfilter the next raw interlaced row into self.unfiltering_buffer.