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Re: Clipping Issue

To: REALbasic Games <realbasic-games at lists dot realsoftware dot com>
Subject: Re: Clipping Issue
From: Frank Condello <developer at chaoticbox dot com>
Date: Wed, 6 Dec 2006 00:08:52 -0500
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Delivered-to: realbasic-games at lists dot realsoftware dot com
References: <20061130180035 dot 7694116C3D50 at lists dot realsoftware dot com> <d9269eb1537baecfa895627f009814ef at 98115 dot net>
On 5-Dec-06, at 10:59 PM, Craig Macomber wrote:

I have many rendered objects that are close together, (HUD, world (Tunnel), and shadows) which are having clipping issues. I believe this is called Z fighting. My Shadows (even if I make then quite far apart, like almost 1% of my entire scene depth)

To improve this, I have tried increasing the hither, decreasing the yon, removing my furthest objects (making the scene 1/5 as deep), changing the texture sizes, and nothing helped other than simply turning off the alpha mask for the tunnel.

A picture can be found at http://img215.imageshack.us/img215/7946/ clipbuguv6.jpg

This doesn't look like z fighting, but rather an artifact of Quesa's per-triangle sort. The shot in the lower left kinda gives this away, and the fact that it goes away when you turn off the tunnel's alpha confirms it. The clipping is simply caused by a big triangle (part of the tunnel) drawing on top of everything else, because it has been determined to be "in front" - sorting big triangles is tricky, and Quesa doesn't accept sorting hints so you're stuck with whatever it gives you.

The tunnel seems to be the cause. When even one of the objects passes over one of the edges between the triangles it has the problem. If I turn the Alpha mask off on the tunnel the problem is fixed, but I don't want to do that.

If you can get away with using a 1 bit alpha test on the tunnel instead of a full alpha blend that should "fix" the problem at the cost of image quality. Other than that there's not much that can be done short of hacking Quesa.

Frank.
<http://developer.chaoticbox.com/>
<http://macgameblog.com/>


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