Re: Layer anomalies
John Rohlf (jrohlf++at++tubes)
Wed, 22 Mar 95 10:32:10 PST
>
>
> Ran Yakir, Gary Hall, Dr. Goh Eng Lim, Michael Jones, Allan Schaffer,
> Angus Dorbie, and all other co-planar polygon, z-buffer, pfLayer, pfDecal,
> etc experts:
>
> We are still struggling with co-planar planes and z-buffering in our
> application. In our database the roads are co-planar with the terrain.
> These causes the roads to be "Z fighting" or "flimmering" like the man
> pages describe them.
>
> Ran, we have tried to setup stencils using the stensize() command with no
> difference in the behavior of our application. Maybe we are not inserting
> the calls in the right place? Can you more specific as to were this command
> should be placed within the program.
>
> Allan, we are staying away from "stitching" the road polygons because it
> will have to be done manually and there is a lot of roads, rail roads,
> rivers and other networks. Maybe somebody out there has an algorithm that
> will implement this "stitching" function. The algorithm will replace the
> terrain polygons with road polygons, however this is not a trivial task so
> we are also staying away from developing such algorithm.
>
> Angus, we are also staying away from modifying the z-buffer before and after
> drawing the road polygons because we are running on an Indigo Extreme and
> it will kill our frame rate (15 Hz).
>
> The best solution so far is being to label the roads as subfaces. This
> has taken care of the "shimmering" polygons but it has created another
> rendering anomalies. Some times depending on the angle and view point
> location roads can be seen through hills and buildings. The only changes
> here is to the database, and the anomalies can be seen using Perfly. We
> have tried stensize() calls but they do not seam to make any difference.
> Can anybody explain what Performer is doing when it sees this sub-face
> polygons and why we are seen this rendering anomalies.
>
> We have placed a copy of the database in our anonymous ftp site for all of
> those that will like to take a look at these anomalies and maybe suggest a
> fix to this problem. The database can be viewed with Perfly or any other
> program the will load a Flight 14.X format database.
>
> The ftp site is "ftp.vsl.ist.ucf.edu" and the files are in the following
> directory:
>
> /pub/vtb/graf_tdb
>
> There are two files in there:
>
> terrain.tar.Z and
> terrain.uu
>
> The terrain.tar.Z is a UNIX LZW compressed tar file of the database
> and terrain.uu is a uuencoded version of file terrain.tar.Z.
> Please feel free to ftp the database or let me know if you will like
> me to e-mail it to you.
>
>
> thanks
> |
> |\
> | \ /
> |/ /
> / .
> .... ... ...
> ... )\ )\
> / . \ / \ / \
> ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
> Benito Graniela University of Central Florida
> Visual Systems Lab Institute for Simulation & Training
> (407) 658-5075 3280 Progress Drive
> bgraniela++at++vsl.ist.ucf.edu Orlando, FL 32806-0544
> ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
Performer uses displacepolygon() for fast rendering
and stencil() for not-so-fast rendering of coplanar geometry.
Unfortunately, IrisGL's displacepolygon() is inadequate in
certain situations - you can see poke through when layers
have large z-slopes and flimmering when they have small z-slopes.
Note that if you specify PFDECAL_BASE_HIGH_QUALITY when
building your Performer database (See pfLayerMode) you will always get
accurate coplanar rendering. You need not call stensize() nor stencil().
I am currently working on a fix for the
displacepolygon() problem that will be available in 2.0
and will experiment with your database.
This archive was generated by hypermail 2.0b2
on Mon Aug 10 1998 - 17:51:06 PDT