Here are the answers: It's not possible for the time being, WKWebView does not expose enough public API to support what i'm trying to do which let WKWebView works like a offscreen component instead of a UI view control. There is no faster way to access the pixel data from the CGImage.

Regarding upload CGImage pixel data to MTLTexture, i also tried vImage acclerated API, the performance bottleneck still lies on vConvert_PermuteChannels_ARGB8888_CV_vec, considering the function name start with "v", i guess it's already SIMD like instruction set accelerated. and channel permute operation looks like can't be avoided.