How to Stretch image result from SKGLView?

[MathieuJack]

I am drawing some painting into a SKGlView.
Gl is important, because I need hardware acceleration, in a render loop.
I need to downscale the drawing result into an offscreen image. My problem is that SKGlView renders into a SKSurface, but SKCanvas can't do stretching (=having source size different from dest size) using a SKSurface (while it can with a SKBitmap)
I can't clone the SKGlView's surface into a SKBitmap because it is slow (not hw accelerated)
So, how to stretch the drawing result of a SKGlView?