Enum `Adam7Variant`

#[non_exhaustive]
pub enum Adam7Variant

The algorithm to use when progressively filling pixel data from Adam7 interlaced passes.

Adam7 interlacing is a technique optionally used in PNG by which only a sub-sample of pixel data is encoded in the beginning of the image data chunks, followed by progressively larger subsets of the data in subsequent passes. Therefore a 'rough image' is available after ust a very tiny fraction of the data has been read which can be advantageous for loading an image from a slow IO medium while optimizing time-to-first-meaningful-paint and then replacing the presented data as it is streamed in.

There are trade-offs to make here. The strictly necessary requirement for an implementation is that the exact image is recovered after all passes are applied. However the intermediate states of the output are left to the implementation, as long as it follows the restriction of resulting in the intended image when all passes have been applied.

Variants

Sparse

This is the adam7 de-interlace we do by default. Only pixels related to the pass are written. The output buffer should not be directly used for presentation until all passes are complete. At least the invalid pixels in the buffer should be masked. However, this performs the least amount of writes and is optimal when you're only reading full frames.

This corresponds to expand_interlaced_row.

Splat

A variant of the Adam7 de-interlace that ensures that all pixels are initialized after each pass, and are progressively refined towards the final image. Performs more writes than the other variant as some pixels are touched repeatedly, but ensures the buffer can be used as directly as possible for presentation.

This corresponds to splat_interlaced_row.