Enum ImageSequence 

#[non_exhaustive]
pub enum ImageSequence {
    Single,
    Animation {
        frame_count: Option<u32>,
        loop_count: Option<u32>,
        random_access: bool,
    },
    Multi {
        image_count: Option<u32>,
        random_access: bool,
    },
}

What kind of image sequence the file contains.

Determines which decoder trait is appropriate:

• Single → Decode
• Animation → AnimationFrameDecoder
• Multi → future MultiPageDecoder (or Decode for primary only)

Key invariant

The variant tells you which decoder trait applies. Code that sees Multi knows not to use AnimationFrameDecoder. Code that sees Animation knows MultiPageDecoder is wrong. Single means only Decode is needed.

Variants (Non-exhaustive)

Non-exhaustive enums could have additional variants added in future. Therefore, when matching against variants of non-exhaustive enums, an extra wildcard arm must be added to account for any future variants.

Single

Single image. Decode returns it.

Animation

Temporal animation: frames share a canvas size, have durations, and may use compositing (disposal, blending, reference slots).

Use AnimationFrameDecoder.

Fields

frame_count: Option<u32>

Number of displayed frames. None if unknown without full parse (e.g., GIF requires scanning all frames to count them).

loop_count: Option<u32>

Loop count: 0 = infinite, N = play N times. None = unspecified.

random_access: bool

Whether frame N can be rendered without decoding frames 0..N-1.

True when all frames are full-canvas replacements (no disposal dependencies). False for GIF/APNG with inter-frame disposal. JXL is typically true (keyframe-based).

Multi

Multiple independent images in a single container.

Pages may differ in dimensions, pixel format, color space, and metadata. Decode returns the primary image only. Other images require a MultiPageDecoder (future) or the codec’s native API.

Examples: multi-page TIFF, HEIF collections, ICO sizes, DICOM slices, GeoTIFF spectral bands.

Fields

image_count: Option<u32>

Number of primary-level images, excluding thumbnails, masks, and pyramid levels (those are reported via Supplements).

None if unknown without full parse.

random_access: bool

Whether image N can be decoded without decoding images 0..N-1.

True for most container formats (TIFF IFDs, HEIF items, ICO entries) where each image is independently addressable.

Implementations

impl ImageSequence

pub fn count(&self) -> Option<u32>

Frame/image count if known.

• Single → Some(1)
• Animation → frame_count (may be None)
• Multi → image_count (may be None)

pub fn random_access(&self) -> bool

Whether individual frames/images can be accessed without decoding all priors.

pub fn is_animation(&self) -> bool

Whether this is an animation sequence.

pub fn is_multi(&self) -> bool

Whether this contains multiple independent images.

Trait Implementations

impl Clone for ImageSequence

fn clone(&self) -> ImageSequence

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for ImageSequence

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

Formats the value using the given formatter.

impl Default for ImageSequence

fn default() -> ImageSequence

Returns the “default value” for a type.

impl PartialEq for ImageSequence

fn eq(&self, other: &ImageSequence) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Eq for ImageSequence

impl StructuralPartialEq for ImageSequence