Screensaver oddity

[tag]

Ok, it seems on some of my screensavers, that there is a clear line which scrolls from the bottom of the screen to the top of the screen. Now this only seems to be happening on the screensavers which are constantly moving fast, (such as the Flurry one that comes with Tiger), the ones which just zoom in and out of different pictures do not seem to be affected.

The clear line is seen as it distorts the moving/swirling image as it moves up the screen. Its a bit hard to describe but has anyone encountered anything like that? This happens multiple times a minute, and while it doesn't seem to be causing a problem, it is quite annoying.

 

[TMA]

Is it an 'invisible' line? Above the line the image does not quite match whats underneath the line? If so, I believe it's something to do with the graphics card not syncing with the refresh rate of your screen. It happens to me with fast moving graphics and i've put it down to the fact i've only got a Geforce 5200FX. Someone that understands graphics cards could explain abit better.

 

[tag]

Is it an 'invisible' line? Above the line the image does not quite match whats underneath the line? If so, I believe it's something to do with the graphics card not syncing with the refresh rate of your screen. It happens to me with fast moving graphics and i've put it down to the fact i've only got a Geforce 5200FX. Someone that understands graphics cards could explain abit better.

Ah yes, you explained it better than me I think. Thats exactly what happens. I also have a Geforce FX 5200 64MB card in my iMac. You say its probably not syncing with the refresh rate of the screen, does that mean there could be something wrong with the card or just that the card isn't fast enough to cope with the graphics?

 

[TMA]

I highly doubt it's a problem with your graphics card or computer. I've seen it happen on several computers before (PC and Mac)

I really wouldn't like to say for definite because I'm not into graphics cards/gaming or 3D in general. What I'm about to say is probably completely wrong. I think that if a 3D Scene or fast moving video taxes the GPU then the frame rate, although still well into the range that the human eye perceives as fluid movement, will overlap the refresh rate of your display. The display then doesn't have all the information it needs. so you get a quick flash with the 'invisible line'.

I also know there's a feature in some games/applications called 'Vsync' (Vertical Syncronisation) which is supposed to remedy this, but it's more work for the graphics card to time itself to the display and so you loose some performance (how much I don't know)

I'd be interested to know some details on this too, from someone that knows this area a little better!

 

[tag]

Ok, this makes it a bit more odd. I downloaded a program called Backlight, which lets you display a screensaver as a background. When its running through the program, the invisible line is gone, and the screensaver is perfectly smooth. So I find that a bit weird, but at least I have a way to display it now, without the little glitchy invisible line.