-- If the device is REAGL-aware, and we're doing a PARTIAL *reader* refresh, apply some trickery to match the stock reader's behavior if needed (On *some* devices, REAGL updates are always FULL, but there's no black flash)
-- On the other hand, if we asked for a PARTIAL *UI* refresh, fall back to the default waveform mode, which is tailored per-device to hopefully be more appropriate in this instance than the one we use in the reader.