some technical questions about consoles (Erp, Far...)

Hmm, really? Why does AA nulify Z compression?

 

It has to do with how the compression works and how the framebuffer is arranged in quincunx mode. This particular effect is unique to the quincunx sample arrangement.
The net result is that although the ZCompression hardware is still functional, it will rarely actually compress anything.

 

So this effect will only happen with Quincunx.. as in 2xMSAA with a blur filter. So why not just used 2xMSAA or even 4xMSAA so you can keep the Z-compression. Or is 2xMSAA and blur filter the only AA XBox is allowed to do?[/quote]

 

Sorry to clarify it occurs with or without the 5 tap filter.
There is an additional cost for it's use aswell.
There is no regular sample pattern 2xMS and going to 4xMS which does have a regular arrangement involves a much slower copy forwards operation.

I guess my point is that your going to pay of the order of at least 15% of your frametime probably more like 25% to enable AA, this isn't an issue if you plan for the cost up front. But the developer has to choose early in the process between AA and more geometry/fill complexity. And on your average small TV 2x AA is a relatively small improvement at best.