I have a 4k screen on my laptop which means that if I position a rendered viewport in one quarter I'm rendering on-the-fly a resolution of 1920X1080. My current solution to save time is make the viewport window smaller but then it's harder to see. What I'd really like to do is set a scale for the preview rendering of something like x0.5. In other words, whilst I size the rendered viewport to something like 1920x1080 I actually want Blender to only calculate 960x540.
Is there an option for this in Blender? Otherwise I'll end up down-sizing my resolution before starting Blender :(