Function WebPPlaneDistortion 

pub unsafe extern "C" fn WebPPlaneDistortion(
    src: *const u8,
    src_stride: usize,
    ref_: *const u8,
    ref_stride: usize,
    width: c_int,
    height: c_int,
    x_step: usize,
    type_: c_int,
    distortion: *mut c_float,
    result: *mut c_float,
) -> c_int

Available on crate feature 0_6 only.

Compute the single distortion for packed planes of samples. src will be compared to ref, and the raw distortion stored into *distortion. The refined metric (log(MSE), log(1 - ssim),…) will be stored in *result. x_step is the horizontal stride (in bytes) between samples. src/ref_stride is the byte distance between rows. Returns false in case of error (bad parameter, memory allocation error, …).