Suppose you have a very heavy scene you can’t draw in one step (it takes 4 seconds to draw completely). ZPR would be impossible, even simplifying what to draw in dynamic movements.
Would it be possible to draw a reasonable number of objects, take a snapshot of color and depth buffers and add more objects in subsequent frames at some interval of time? I mean blending previous frame snapshots (buffers) with current ones?
The final effect would be that if the user does not move you see the scene populating progressively at each timer tick, while if the user moves the camera you can interrupt and start over.