I hear you. This is a very old HOWTO that does need to be rewritten, indeed.
But RTSS Scanline Sync is an airplane cockpit compared to other sync technologies and is very hard to explain without raster interrupts knowledge (beam raced tear lines). First, to understand how RTSS Scanline Sync was born: See Tearline Jedi
Now the reason why if you’re using the other sync technologies instead of VSYNC OFF, is that tearline moves downwards on a time-bases, as it follows the Display Scanout (high speed videos)
Once you see the links. You begin to realize tearlines just above bottom edge will take less time to the end of refresh cycle. This is important for sync technologies that waits-til-end-of-refresh (like VSYNC or triple buffering) before showing new frames.
If the tearline is below bottom edge during VSYNC OFF, then turning on a sync technology can add one refresh delay as since it already missed the end of refresh cycle (last pixel row or first line of VBI), the enabled sync technology it waits until the end of the next refesh cycle
before displaying the presented frame, because if the VSYNC OFF tearline is already below screen bottom edge, “the VSYNC is already missed!”, so +1 refresh lag penalty. Might as well turn off Scanline Sync and use plain jane VSYNC ON instead. So if you want less lag with a “non-VSYNC-OFF” RTSS Scanline Sync, you want the tearline as close to VBI (screen bottomedge) but still BEFORE in clock time, as seen in high speed videos at www.blurbusters.com/scanout
... Windows frame presentation triggers at the end of refresh cycle, before the VBI. It’s not the ideal way I want Windows to function, but this is an issue — I prefer that non-VSYNC-OFF technologies blocks until beginning of new refresh cycle and life would be a helluva lot simpler, and we’d already be getting Quick Frame Transport benfits. But we are fighting against the behavior of legacy design Present()-to-Photons black box.
RTSS Scanline Sync is more advanced, and hard to write an easy guide for.
- It’s like University versus Elementary School (VSYNC ON).
- Skill Level 40 versus Skill Level 2.
- Assembly Programming versus BASIC programming
- Pilot cockpit versus car dash
One computer may behave like a brand new Boeing 747 and another computer may behave like a defective Cessna, in how the tearline jitters, cycles, and how easy/stubborn it is to calibrate on different systems. Turning it to child’s play for some, and a hair pulling experience for others. It’s so unusually sensitive to imperfections. I even offered 300 Euros to someone technically literate to write an RTSS Scanline Sync HOWTO....and they failed. So guess I gotta do the dirty job myself, eh?
[Blur Busters is accepting cirriculum-vitae for highly technically literate freelance writers, that understands the Blur Busters concepts of GtG, MPRT, lag, and can branch to these. squad[at]blurbusters.com ...]
That’s the problem of RTSS Scanline Sync in writing easy guides for it.
But, yes, an easier guide will come sometime 2021.