The "analogue oscilloscope" redraw style, you can see in the scope example I mentioned in the earlier "long scope" thread
Now, in principle, the scrolling type scope could be done in a similar way. ..
I mentioned in the earlier thread that a bitmap was used to store previously drawn sections of the display, to avoid the need to store huge arrays and plot lots of graph points.
Something very similar could be used to make a scrolling scope - i.e. for each "frame", scroll the existing bitmap buffer to the left by the appropriate amount - overlay the next small chunk at the right hand side - capture this as a new bitmap buffer - and repeat.
The only potential flaw is that the amount of scrolling for each frame would vary slightly (due to innacurate timers) - not a problem to avoid gaps in the waveform, I already got around that to make the "ReDraw" scope stitch the frames together correctly. However unless bitmaps are scrolled in whole pixels, they become blurred due to anti aliasing - making the waveform gradually more fuzzy as it moves to the left.
You can see something of what I mean in the "waterfall" frequency plotter that I posted HERE
- only the front plot is actually "drawn" - the ones behind it are done purely by manipulating bitmap captures. Not quite what you are looking for, but it does demonstrate that animated audio displays with reasonable CPU load are definitely possible with a bit of graphics trickery.