Tech Question - Vertical Sync
 

What does the "Wait for Vertical Sync" selection do in the "Display Settings" screen do?

Post #657 in the "Comments and Appreciation" thread says:

"After completing the building of a frame, the program waits until the next vertical refresh of the monitor to display it. So the maximum frame rate it could ever achieve is the monitor refresh rate (usually 60 hz). "

You'll find it near the bottom of https://www.feldoncentral.com/forums...t=4382&page=33

When VSync is off, the program can display a new frame as soon as it's built. Odds are, the monitor will be somewhere in the middle of a screen refresh when that happens. In that case, the top part of the screen will still be the old picture, and the bottom part will be the new one. If there are big changes between the two (like rapid scrolling of the scene), then an unpleasant "tearing" effect is seen.

VSync eliminates this problem, but also limits the frame rate to the refresh rate of the monitor.

Thanks.

I noticed that it is set "off" (not checked) in the Display Settings screen.

It would be set "on", then, as a first step in diagnosing a video problem or if one wants to automatically limit the frame rate to equal the refresh rate of a monitor?

I believe setting VSync on does not always necessarily limit the framerate to 60. Usually, but not always.

Windows 2000 and subsequent versions initially set the display rate at the lowest rate supported by the video subsystem. As Jim clearly said (in the reference I quoted), that is usually 60 Hz.

But the user can have changed that to some higher rate supported by his/her system. In which case VSync would limit to that rate, of course. The "side effect" is that simply changing the display settings outside MA3, can change the performance/appearance of MA3.

On many systems, VSync will limit the frame rate to 30. If the system takes slightly more than 1/60 of a second to build a frame, then it's missed the boat for that refresh, and will have to wait for the next one, resulting in an every-other-frame rate.

You'd probably have to have quite an old computer to get tearing at the default panning speed. If I remember correctly this feature was included because intel graphics don't have the option in their control panel to turn Vsync on/off. They don't seem to support AA at all, but I'm not 100% sure on that.

Yes, you'd never notice it at the default speed, but most of my friends go straight for the arrow keys, to enjoy the full 3D effect.

By the way - those arrow keys (if you keep them when you go to the "limit" method) should be described in the About panel, when you get a chance.

Also, if you keep the arrow keys to adjust the "Limit Frame Rate", I suggest that the up-arrow be defined as increasing the frame rate (it now decreases it). Etc.

Since Jim mentioned in another thread that I'm rewriting/revising the readme.txt file for the Windows release, I can explain that that is why I asked the question here.

I'm trying to understand what I should write to explain what happens whether the "wait for vertical sync" box is checked.

Maybe I'll wait a bit to see if that option is actually still in the next beta.

The Vsync option was requested by a user on this forum, so it will probably not be going away. I suppose what you put for your definition depends on how technical you want to get. Maybe you could put in a link to wikipedia? I'd look into it further but I'm about to transmute into guy mode and fit a new drive belt on my lawnmower so I don't have time today. (For the Buffy fans I'm going from Glory to Ben)

Perhaps:

When checked, guarantees that the frame rate of Marine Aquarium will never be faster than the display frame rate set in Windows Display Properties. Note: the MA3 rate may be slower in some cases.

Thanks to all for help and suggestions.

At this point, I'm going with:


"Wait for vertical sync" box is normally not checked. If you experience graphical "tearing" where the animation of the fish and background appear as a series of horizontal strips, instead of a smooth, fluid image, try enabling "Wait for vertical sync". This setting instructs your scomputer to wait until the animation frame has been completely drawn before displaying it on your monitor.

Thanks to Feldon34.