Re: Making holes in pfEarthSky.

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Angus MacDonald Dorbie (dorbie++at++multipass.asd.sgi.com)
Wed, 21 May 1997 09:50:51 -0700

I preffer Steves suggestion, aside from the hole/ground occlusion issues,
to simply clear the depth buffer would incurr a couple of overheads, first,
you are going to have the overhead of writing ground pixels around the hole
one additional time, second you have to clear the screen (clear screen and
stencil for speed on iR).

BTW, Ran Yankir may be an expert at visualising diggers 'n stuff,
I noticed his name in the footnotes of a SigGraph paper a couple of
years ago. He did the real-time visualisation (ie the important bit).

Cheers,Angus.

On May 20, 5:05pm, Steve Baker wrote:
> Subject: Re: Making holes in pfEarthSky.
> > > I am currently working on a simulation of an excavator (used for
digging),
> > > using Performer 2.0 (IRIX 5.3). The excavator has been modelled and is
> > > working well, however animating the digging has proved to be little
> > > tricky. I am able to produce a reasonably convincing hole in the ground,
> > > but am not able to integrate this with the ground created by using a
> > > pfEarthSky. An ideal solution would be the ability to make parts of the
> > > "Earth" transparent, revealing the hole underneith. Is there a way of
> > > doing this?
> >
> > How about drawing like this:
> >
> > 1. Draw pfEarthSky
> > 2. Clear zbuffer
> > 3. Draw everything else
> >
> > This way the holes would not be covered by the Earth (they will overdraw
> > regardless of the pixel z-positions). I can't think of a better way to do
> > it, someone else here probably can.
>
> That might work - providing you don't have a really low eye angle
> such that the soil at ground level (drawn in the esky phase) should
> be occulting the polygons that make up the bottom of the hole.
>
> If the holes are shallow dimples - so that the angle of the sides
> of the hole with respect to the ground is smaller than the angle
> of the eye relative to the bottom of the hole - then you'll be
> OK.
>
> It looks like you can't really get away from drawing the ground
> yourself as a dense mesh of polygons whose elevation and texture
> would be varied as digging progresses.
>
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