Re: Making holes in pfEarthSky.

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Steve Baker (steve++at++mred.bgm.link.com)
Tue, 20 May 97 17:05:07 -0500

> > 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.

Steve Baker 817-619-1361 (Vox-Lab)
Hughes Training Inc. 817-619-8776 (Vox-Office/Vox-Mail)
2200 Arlington Downs Road 817-619-4028 (Fax)
Arlington, Texas. TX 76005-6171 Steve++at++MrEd.bgm.link.com (eMail)
http://www.hti.com (external) http://MrEd.bgm.link.com/staff/steve (intranet)
                                http://web2.airmail.net/sjbaker1 (external)

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