Module snapshot 

Available on crate feature snapshot only.

Perceptual snapshot assertions.

A snapshot is named, and where its bytes come from depends on where the test runs. Natively they are read from the asset submodule beside the test file, so a mismatch can be re-stored in place with SNAPSHOT_UPDATE=1. In a browser there is no filesystem to read or write, so snapshot! embeds the baseline into the wasm binary at the call site instead — and the comparison itself, a real SSIMULACRA2 score, runs there unchanged.

Both paths decode the same WebP and score it the same way; only the origin of the bytes differs.

Re-exports

use image::ImageEncoder; 🔒

use ssimulacra2::ColorPrimaries; 🔒

use ssimulacra2::Rgb; 🔒

use ssimulacra2::TransferCharacteristic; 🔒

use ssimulacra2::compute_frame_ssimulacra2; 🔒

Structs

Comparison 🔒

What comparing a frame against its baseline found.

Snapshot

A snapshot baseline, and where its bytes come from.

Tolerance

How closely a frame must match its snapshot.

Enums

SnapshotError

What went wrong storing or comparing a snapshot.

Constants

DEFAULT_MIN_SCORE

The perceptual score a frame must reach to match its snapshot.

DEFAULT_MISMATCH_DIRNon-WebAssembly

Where mismatched frames are written when MISMATCH_DIR_ENV is unset.

DEFAULT_TOLERANCE

The tolerance a snapshot gets when it names none: the perceptual floor DEFAULT_MIN_SCORE, with no bound on how many pixels may stand out.

MISMATCH_DIR_ENVNon-WebAssembly

The environment variable that collects mismatched frames on the host.

SNAPSHOT_DIR 🔒 Non-WebAssembly

Where Snapshot::on_disk looks a snapshot up by name, relative to the process’s working directory — which for a test is its package root.

Functions

assert_image_snapshot

Assert that rgba matches snapshot within DEFAULT_TOLERANCE.

assert_image_snapshot_with_tolerance

Assert that rgba matches snapshot within tolerance.

check_frame_size 🔒

Reject a frame whose bytes do not describe width x height RGBA pixels.

compare 🔒 Non-WebAssembly

Measure a frame against its baseline, storing one where none exists yet.

compare_frame_bytes 🔒

Measure rgba against a WebP baseline held in memory.

compare_frame_webp 🔒 Non-WebAssembly

Measure the frame rgba against the snapshot at path.

encode_frame_webp

Encode rgba as a lossless WebP.

outlier_fraction 🔒

The fraction of pixels whose largest per-channel difference from the baseline exceeds channel_delta.

rgb_frame 🔒

Turn an RGBA8 frame into the RGB the metric reads.

score_frame_webpNon-WebAssembly

Score the frame rgba against the snapshot at path, on SSIMULACRA2’s 0–100 scale where higher is closer.

snapshot_pathNon-WebAssembly

Where a snapshot named name lives, under the snapshots directory.

store_frame_webpNon-WebAssembly

Write rgba to path as a lossless WebP, creating its directory.

store_mismatch 🔒 Non-WebAssembly

Keep a frame that did not match, so a failing run leaves it behind.