Function WebPConfigLosslessPreset 

pub unsafe extern "C" fn WebPConfigLosslessPreset(
    config: *mut WebPConfig,
    level: c_int,
) -> c_int

Available on crate feature 0_5 only.

Activate the lossless compression mode with the desired efficiency level between 0 (fastest, lowest compression) and 9 (slower, best compression). A good default level is 6, providing a fair tradeoff between compression speed and final compressed size. This function will overwrite several fields from config: method, quality and lossless. Returns false in case of parameter error.