Struct DecodedSource 

pub struct DecodedSource { /* private fields */ }

A producer that decodes a stream on demand, forward only.

Construction parses the header only — no pixel bytes are read — so Image::metadata stays free and laziness holds (SPEC §Guarantees 3).

Memory

Constant, and independent of image height: the decoder is advanced to the requested band and exactly that band is retained as a rolling window. This is what makes SPEC §Guarantees 1 true for streaming formats — the whole image is never resident.

The window also absorbs repeated demand for the same band, which is what lets two graph branches share one source without either re-reading a stream that has already moved on.

Forward only

A request that starts before the window is an error, not a rewind: the bytes are gone (ADR-0005). The scheduler is responsible for never asking — Plan detects non-forward demand ahead of time and materializes instead (ADR-0009). Reaching this error therefore indicates a scheduling defect, and it is reported rather than papered over.

Implementations

impl DecodedSource

pub fn new(decoder: Box<dyn Decoder>) -> Self

Wrap a decoder whose header has been parsed.

No pixel rows are read here.

Trait Implementations

impl Debug for DecodedSource

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Producer for DecodedSource

fn name(&self) -> &'static str

A short, stable name for this producer, used in diagnostics.

fn descriptor(&self) -> ImageDescriptor

The shape of the image this producer yields.

fn capability(&self) -> DecodeCapability

Whether this producer can serve arbitrary regions, or only forward ones.

fn reduced_descriptor(&self, target: (u32, u32)) -> Option<ImageDescriptor>

What this producer would emit if asked for target or larger, when it can reach that size more cheaply than by producing full resolution.

fn reduce_to(&self, descriptor: ImageDescriptor) -> Result<()>

Commit to emitting descriptor, which Producer::reduced_descriptor must have returned.

fn produce(&self, region: Region, output: &mut TileMut<'_>) -> Result<()>

Fill output with the pixels of region.