pratt@TAURUS.CS.NPS.NAVY.MIL (david pratt) (02/28/91)
Greetings, We are working on a 3D vehicle simulator, called NPSNET, and it is working quite well. We have 500 vehicles moving over the terrain in real time with texture and fog on a 4D 240/VGX. But all is not happy at Zydaville (the town in the simulator)! When the texturing is turned on, with scrsubdivide set to 10 pixels, I get a polygon edge mismatch. This results in the clear color showing through the terrain. It is very noticeable when we sail the ships on the ocean or drive/fly over large flat areas. I have subpixel(TRUE) on and tried polysmooth(PYSM_ON) with no luck. Does anybody out there in netland have any ideas? How about SGI? Dave -- Dave Pratt pratt@cs.nps.navy.mil (408) 646-2865 If the meek shall inherit the earth, I'm SOL! These are my opinions, who knows what the Navy thinks.
rad@home.asd.sgi.com (Bob Drebin) (03/01/91)
You have to be careful when using scrsubdivide(). As noted in the man page: When the screen size of subdivided polygons is limited, either by minsize or by maxsize, adjacent polygons can subdivide differently such that newly created vertices on their shared boundary do not coincide. In this case, some pixels at their shared boundary may not be scan converted by either polygon. I can suggest two solutions: 1) Only use maxz to control subdivision. Disable minsize and maxsize by setting them to zero. This will prevent T-verticies from being generated, which cause the pixel dropouts. 2) Use anti-aliased lines. Draw your scene using your current scrsubdivide parameters, then redraw the outlines of troublesome polygons using anti-aliased lines. For example: /* draw the scene */ zbuffer(TRUE); blendfunction(BF_ONE,BF_ZERO); scrsubdivide(SS_ON,myparms); draw_terrain(); scrsubdivide(SS_OFF,myparms); draw_nontextured_stuff(); /* redraw outlines of textured polys */ blendfunction(BF_SA,BF_MSA); polymode(PYM_LINE); linesmooth(SML_ON); scrsubdivide(SS_ON,myparms); draw_terrain(); Hope this helps. Bob Drebin, SGI P.S.: The function polysmooth does not work with textured polygons. This is noted in its man page.