From: Angus Dorbie (dorbie++at++sgi.com)
Date: 03/01/2001 13:01:18
OK, if this is only the diffuse term and no specular effects (which
would lead to localviewer issues) then problem is probably some
interaction of clipping and non perspective correct gouraud shading.
This is pretty insurmountable really, you could try mapping the light
source diffuse term as a texture, a 2D texture could give you two
lights, 3D could give you 3 lights. You'd then do a manual L.N
calculation and map the terms for the 3 light source L.N products to
s,t&r, this would give you perspective correct interpolation and correct
clipping and therefore eliminate the artifacts you are seeing.
This would work best where the light sources were not moving.
A very small 3D texture where the image stored an additive ramp along
each of the axes. Colored lights would work just fine. Modulate with a
constant polygon color to do diffuse material modulation.
Cheers,Angus.
Jason Coposky wrote:
>
> everyone,
>
> the scenario:
> we are drawing multiple channels of the same
> scene in a channel group, using channel offsets
> to create a partial cube map, which is then used
> to texture special geometry. this cube map would be
> a cube which was rotated 45 degress such that the
> corner would be along the -z axis in ogl. we then render
> images of the left, right, top and bottom "walls" of the cube.
>
> the problem:
> given a light model which is set to local, i am still seeing
> lighting dicontinuities across the channel boundaries
> ( diffuse i believe ), which is especially noticable after
> texturing our geometry with the partial cube map.
>
> notes:
> this problem arose in our open gl implementation,
> which we corrected by (1) moving our "channel offsets"
> into the projection matrix OR (2) applying precalculated
> model-view transforms to the lights before they
> were drawn. ( as well as setting the light model to local
> viewer to fix specular issues )
>
> the questions:
> * how are the channel offsets dealt with in the pipeline?
> i would imagine them to be applied to the model-view
> matrix to keep the fog calcs proper.
> * what is the obvious thing that im missing?
>
> a simple hack of the simple.C app is included for perusal.
> the final texturing isnt done, but the 3 channels are drawn
> and the discontinuities are noticable. the light model is set
> to local and a red ambient color is added, showing that the
> light model is applied to the scene. ive had the same results
> with both pfLights and pfLightSources and various other attempts.
>
> thanks.
>
> ~J
>
> -----------------------------------------------
> //CC -o ltest lighttest.cpp -L/usr/lib32/ -lpf_ogl -lpfdu_ogl -lpfutil_ogl
> -lGLU -lGL -lXmu -lXext -lX11 -lm
> //
> //
> // Copyright 1995, Silicon Graphics, Inc.
> // ALL RIGHTS RESERVED
> //
> // UNPUBLISHED -- Rights reserved under the copyright laws of the United
> // States. Use of a copyright notice is precautionary only and does not
> // imply publication or disclosure.
> //
> // U.S. GOVERNMENT RESTRICTED RIGHTS LEGEND:
> // Use, duplication or disclosure by the Government is subject to
> restrictions
> // as set forth in FAR 52.227.19(c)(2) or subparagraph (c)(1)(ii) of the
> Rights
> // in Technical Data and Computer Software clause at DFARS 252.227-7013
> and/or
> // in similar or successor clauses in the FAR, or the DOD or NASA FAR
> // Supplement. Contractor/manufacturer is Silicon Graphics, Inc.,
> // 2011 N. Shoreline Blvd. Mountain View, CA 94039-7311.
> //
> // Permission to use, copy, modify, distribute, and sell this software
> // and its documentation for any purpose is hereby granted without
> // fee, provided that (i) the above copyright notices and this
> // permission notice appear in all copies of the software and related
> // documentation, and (ii) the name of Silicon Graphics may not be
> // used in any advertising or publicity relating to the software
> // without the specific, prior written permission of Silicon Graphics.
> //
> // THE SOFTWARE IS PROVIDED "AS-IS" AND WITHOUT WARRANTY OF ANY KIND,
> // EXPRESS, IMPLIED OR OTHERWISE, INCLUDING WITHOUT LIMITATION, ANY
> // WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
> //
> // IN NO EVENT SHALL SILICON GRAPHICS BE LIABLE FOR ANY SPECIAL,
> // INCIDENTAL, INDIRECT OR CONSEQUENTIAL DAMAGES OF ANY KIND, OR ANY
> // DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS,
> // WHETHER OR NOT ADVISED OF THE POSSIBILITY OF DAMAGE, AND ON ANY
> // THEORY OF LIABILITY, ARISING OUT OF OR IN CONNECTION WITH THE USE
> // OR PERFORMANCE OF THIS SOFTWARE.
> //
> //
> // simpleC.C: simple Performer program for programmer's guide
> //
> // $Revision: 1.10 $
> // $Date: 1995/11/22 14:35:21 $
> //
>
> #include <stdlib.h>
>
> #include <Performer/pf/pfChannel.h>
> #include <Performer/pf/pfLightSource.h>
> #include <Performer/pf/pfNode.h>
> #include <Performer/pf/pfScene.h>
>
> #include <Performer/pr/pfLight.h>
>
> #include <Performer/pfutil.h>
> #include <Performer/pfdu.h>
>
> //
> // Usage() -- print usage advice and exit. This
> // procedure is executed in the application process.
> //
> static void
> Usage (void)
> {
> pfNotify(PFNFY_FATAL, PFNFY_USAGE, "Usage: simpleC file.ext ...\n");
> exit(1);
> }
>
> pfLight* Sun;
>
> pfGeoState* curState;
>
> void pwConfig( pfPipeWindow* _pw )
> {
> _pw->open();
>
> pfLightModel* ltm = new pfLightModel;
> ltm->setLocal( PF_ON );
> ltm->setAmbient( 1.0, 0.0, 0.0 );
> ltm->apply();
>
> Sun = new pfLight;
> Sun->setPos( 0.0, 0.0, 0.0, 1.0 );
> Sun->on();
>
> pfOverride( PFSTATE_LIGHTMODEL, PF_ON );
> }
>
> int
> main (int argc, char *argv[])
> {
> float t = 0.0f;
>
> if (argc < 2)
> Usage();
>
> // Initialize Performer
> pfInit();
>
> // Use default multiprocessing mode based on number of
> // processors.
> //
> pfMultiprocess( PFMP_DEFAULT );
>
> // Load all loader DSO's before pfConfig() forks
> pfdInitConverter(argv[1]);
>
> // initiate multi-processing mode set in pfMultiprocess call
> // FORKs for Performer processes, CULL and DRAW, etc. happen here.
> //
> pfConfig();
>
> // Append to Performer search path, PFPATH, files in
> // /usr/share/Performer/data */
> pfFilePath(".:/usr/share/Performer/data");
>
> pfNode *root = pfdLoadFile(argv[1]);
> if (root == NULL)
> {
> pfExit();
> exit(-1);
> }
>
> // Attach loaded file to a new pfScene
> pfScene *scene = new pfScene;
> scene->addChild( root );
>
> // Create a pfLightSource and attach it to scene
> //scene->addChild(new pfLightSource);
>
> // Configure and open GL window
> pfPipe *p = pfGetPipe(0);
> pfPipeWindow *pw = new pfPipeWindow(p);
> pw->setWinType(PFPWIN_TYPE_X);
> pw->setName("IRIS Performer");
> pw->setOriginSize(0,0,500,500/3);
> pw->setConfigFunc( pwConfig );
> pw->config();
>
> // Create and configure a pfChannel.
> pfChannel *chanL = new pfChannel(p);
> pfChannel *chanR = new pfChannel(p);
> pfChannel *chanF = new pfChannel(p);
>
> chanL->setViewport( 0.0, 0.3333, 0.0, 1.0 );
> chanF->setViewport( 0.3333, 0.6666, 0.0, 1.0 );
> chanR->setViewport( 0.6666, 1.0, 0.0, 1.0 );
>
> pfVec3 xyz ( 0.0, 0.0, 0.0 );
> pfVec3 hprL( 90.0, 0.0, 0.0 );
> pfVec3 hprR( -90.0, 0.0, 0.0 );
> pfVec3 hprF( 0.0, 0.0, 0.0 );
>
> chanL->setViewOffsets( xyz, hprL );
> chanR->setViewOffsets( xyz, hprR );
> chanF->setViewOffsets( xyz, hprF );
>
> chanF->setShare( PFCHAN_FOV |
> PFCHAN_VIEW |
> PFCHAN_NEARFAR |
> PFCHAN_SCENE );
>
> chanF->attach( chanL );
> chanF->attach( chanR );
> // determine extent of scene's geometry
> pfSphere bsphere;
> root->getBound(&bsphere);
>
> chanF->setNearFar(0.001f, 10.0f * bsphere.radius);
> chanF->setScene(scene);
> chanF->setFOV(90.0f, 0.0f);
>
> pfEnable( PFEN_LIGHTING );
>
> // Simulate for twenty seconds.
> while ( 1 )//t < 20.0f)
> {
> pfCoord view;
> float s, c;
>
> // Go to sleep until next frame time.
> pfSync();
>
> // Initiate cull/draw for this frame.
> pfFrame();
>
> // Compute new view position.
> t = pfGetTime() / 2.0 ;
>
> pfSinCos(45.0f*t, &s, &c);
> view.hpr.set(45.0f*t, 0.0f, 0);
> view.xyz.set(
> #if 1
> 0.0, 0.0, 0.0 );
> #else
> 2.0f * bsphere.radius * s,
> -2.0f * bsphere.radius * c,
> 0.5f * bsphere.radius );
> #endif
>
> chanF->setView(view.xyz, view.hpr);
> }
>
> // Terminate parallel processes and exit
> pfExit();
> return 0;
> }
>
> -----------------------------------------------
>
> // =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
> Jason M. Coposky, 3D Software Engineer
> jasonc++at++elumens.com
> // =-=-=-=-=-=-=-=-=-=
>
> -----------------------------------------------------------------------
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This archive was generated by hypermail 2b29 : Thu Mar 01 2001 - 13:01:48 PST