@huw while reviewing this patch I noticed that we're temporarily currently modifying stretch_blt_mode of the *source* DC, as introduced in 4a4b5d407c30dc79a632ec8c024566e5d096e47e.
I'm inclined to think that this was a mistake, since the stretch blit mode of the source DC should not affect the stretching operation. Should we fix it in this MR, or can we do it in another MR?