I’m using a clipping map to remove unwanted geometry but am still seeing faint artifacts along the edges of the object which is being clipped away — not along the clipped edge itself, but along the outer limits of the geometry which is being clipped away.

The object being clipped is phong shaded and is floating over an area of raytraced transparency.

This is in 6.5.2 running on Tiger.

http://homepage.mac.com/marsviolet/.Public/fpbottle.jpg

Incidentally, I know I can work around this by rendering two passes — in fact, I have already done so — but I hate workarounds and just want to know if clipping maps can be used successfully with raytraced transparent objects, and if so, what’s the trick?

From your description, it is difficult to know what you are clipping. 

One thing you may try is making the clipping map larger than what is clipped.  You might also play with the sampling rate, the higher the rate 2X2, or 4X4 may help.  Also in the preferences>drawing>fractional digits a larger number may help.

You might also try making it a transparency map, as opposed to a clipping map.  For some reason you can get different results that way.

I like the rendering, the lighting, textures, and reflections are very nice.  The bubbles at the ‘water line’ are a nice touch.  I’m sure you have a happy client.

Yon

Oh, it’s the label I’m clipping. Because I’m basically lazy, rather than modeling geometry in the exact size and shape of the label, I just duped the bottle and am using the label artwork’s alpha channel as a clipping map. Works great so long as I don’t render the bottle and the label at the same time.

Thanks for the suggestions. I haven’t tried any of that stuff yet, so I’ll give it a go and see what happens.

I guess you tried making the label render as raytrace?

On a side, it’s funny how you say you don’t like workarounds, yet the problem you’re having is because you’re using one

BJMonkey - 11 May 2008 07:32 AM

I guess you tried making the label render as raytrace?


On a side, it’s funny how you say you don’t like workarounds, yet the problem you’re having is because you’re using one

Ha ha — a workaround for my laziness maybe, but not a workaround in the traditional sense as a way to work around a feature which isn’t behaving as expected. Clipping maps are a feature.

But yeah, I did try setting the label to raytrace at the item level.

Nice looking render, btw.  Are you lighting with HDR only?

No HDR at all, actually. Just raytracing.

And for the time being, I’ve managed to work past the problem. I just hope it doesn’t crop up again down the road.

Here’s how the bottles look.