Struct CompareContext 

pub struct CompareContext { /* private fields */ }

Reusable scratch buffers for Ssimulacra2Reference::compare_with.

Ssimulacra2Reference::compare allocates roughly 13 image-sized Vec<f32> planes (mul, mu2, sigma2_sq, sigma12, img2_planar) plus the Blur working memory on every call. When you compare many distorted images against the same reference (encoder rate-distortion search, simulated annealing, picker training), reuse a CompareContext to amortise those allocations across all calls. Buffers grow only on the first call and are reused thereafter; later calls do no Vec heap allocation.

Allocated for a specific reference dimension via Ssimulacra2Reference::compare_context; passed to Ssimulacra2Reference::compare_with.

Send but not Sync — give each worker thread its own context.