fn open(settings: &CaptureSettings) -> Option<GpuCapture>Expand description
Build the zero-copy capture for these settings, or report why it cannot serve them.
Everything fallible happens here, before a single frame is delivered, so the caller can fall back to the XShm path with nothing half-built. The server is asked first, over a connection of our own, because whether it draws on the GPU at all, and on which device, is its answer to give; the encoder is built on the device the server named.