jdMorgan - 12:52 am on Jul 12, 2006 (gmt 0)

> Could you explain how one would notice if there are multiple rendering attempts?

The simplest example is multiple-column pages laid out using <table> --like the WebmasterWorld home page-- when the columns do not have a specified width.

In this case, if the content for the second column is delayed, you will see the page rendered with the left-most column taking the full width of the screen. A short time later, you'll see the first column shrink in width, as the second column renders to the right of it. This can happen with any number of columns greater than 1.

The delay in the browser receiving the second-column markup to be rendered could be due to connection-related delays, or perhaps delays in a script or a database lookup on a busy server.

But regardless of the reason, the effect is that you see "things moving around or changing size" on the screen.

You can also see this on busy "graphics-and-ad-rich" sites like The Weather Channel, but they're not good for setting/testing the browser settings because they are just "too slow" on their own, due to all the image requests from external ad servers, image servers, etc. I very rarely see sites like that that *don't* force at least one re-rendering pass during their "busy hours" when one or more of the servers get back-logged. But they make good examples to watch for re-rendering cycles if you want to see them.

I recommended "setting nglayout delay to the longest you can stand," and then adjusting down until this happens. I always end up somewhere around the default value anyway, but the number I start with -- the longest I can stand -- is admittedly only about 750 mSecs anyway... :)

The minimum visually-perceptible timeframe affected/affects the design of many systems -- The frame rate of motion pictures, the refresh rate/response time of television and computer monitors, etc. When frame/refresh rates are too slow, we perceive this as a 'flickering' on the screen. At 50 cycles per second (20 mSec per frame), the flicker is just barely perceptible, but can be quite annoying over long sittings. Raise the frequency just a little bit to 60 Hertz or 16.7 mSecs, and most people can no longer see the flicker. And at 14mSecs, almost no-one can perceive it.

Jim