>MIME-Version: 1.0
>Date: Tue, 17 Apr 2001 10:53:49 -0400
>From: "Yazel, David J." <[EMAIL PROTECTED]>
>Subject: [JAVA3D] How to lay down geometry on top of other geometry?
>To: [EMAIL PROTECTED]
>
>We have been experimenting with laying paths and roads on top of our
>terrain.
>
>Examples:
>
>http://www.cosm-game.com/screenshots/cosm345.jpg
>http://www.cosm-game.com/screenshots/cosm347.jpg
>
>We build an articulated triangle strip by applying bezier curves to a series
>of path nodes, then flattening the curves by sub-dividing, then turn them
>into a series of equally spaced nodes at a certain density, then finally
>turning that into a triangle strip.
>
>We do this for a number of reasons, the primariy one being that we can apply
>a higher density texture to the path than we use for the terrain. This also
>allows us to "flow" a texture along the path, such as stone or brick.
>
>The height of each point in the path mesh is retrieved from the heightmap
>source. Laying it over the terrain has some issues. The first one is that
>the path mesh is actually more accurate than the terrain mesh, since the
>terrain is rendered with a lower density and has slight errors due to edge
>collapsing we do to reduce polygon count.
>
>This means that the path sometimes dips below the ground.
>
>1. I have tried adjusting the polygon offset and offset factor to give the
>path zbuffer precedence but this didn't seem to do anything.
>
In case you are using DirectX version of Java3D,
only negative polygon offsets are supported due to
limitation of Direct3D.
>2. The path mesh has alpha blended edges, so I don't think I can Decal it on
>top of the terrain, not to mention that the terrain is in chunks and I would
>have to break up the path and attach the segment to each chunk. If I did do
>that, how exactly is decal implemented? The documents say that decals have
>to be coplanar, then say they dont guarentee there will be no zbuffer
>collisions... which makes no sense to me. What blend modes are supported
>with Decals?
>
>3. I tried disabling zbuffer reads for the path, and this works fine as long
>as you are looking down the path, but if the path loops around the hill you
>now see it through the hill.
>
>4. I tried adding an arbitrary Y addition to deal with the terrain
>discrepencies, and this produced the best results, but still far from
>perfect.
>
>Does anyone have any suggestions?
>
>Dave Yazel
>Cosm Development Team
>http://www.cosm-game.com/
>
- Kelvin
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