Hi Eric, You are correct that what I saw was much like your Artifacts128.png.
Most of my stress testing has been on ATI since its artifacts are so obvious; I haven't tried hard to cause on NV but I'll try when I have a chance. I'll try to adjust the parameter and report my results. Where exactly is the offset parameter to adjust? (sorry I'm a bit pressed for time) Thanks -- mew E. Wing wrote: >> Date: Tue, 11 Jul 2006 10:09:32 +0100 >> From: "Robert Osfield" <[EMAIL PROTECTED]> >> Subject: Re: [osg-users] sigh: osglogo 1.1rc1 on ATI > > >> Hi Eric/Mike, >> >> I think for 1.1 we should experiment with what mulitpliers work on >> different hardware, and then come up with some auto detection code >> that detects the hardware and produces an appropriate fudge setting >> for it. If could be a simple as its ATI then use 512 as a multiplier, >> it could be that this should go into osg::PolygonOffset itself. > > > Unfortunately, I don't think there is one perfect value for the ATI > cards. I've been experimenting with the values more and there seem to > be two different z-fighting cases that conflict with each other. For > small multipliers, I'm getting the artifacts that I originally > complained about and I think Mike is also complaining about. (see > attached Artifacts128.png) You see holes/gaps in the the glyphs and if > you rotate the text quickly, they come and go in different spots very > quickly which gives an unplesant 'flickering' effect. Pumping up the > fudge multiplier helps remove this effect. I noticed that Nvidia gets > it too occasionally at the current 2x multiplier. Pumping this value > up helped there as well. For ATI, I found that 128 still has some of > these artifacts (which the picture is set to). Going up to 150 might > be the minimal acceptable value where flickers are few, though I think > I'm slightly more comfortable with 192. At 512, I don't notice these > effects any more. (FYI, if I disable the textures, and just look at > the polygons, there are no holes/artifacts so its partially related to > texturing.) > > But pumping up the offset multiplier too high seems to lead to a > different z-fighting problem. (see attached Missing192.png). When > zoomed in, and looking at extreme angles, it seems that some or all of > the backdrop polygons completely disappear from being rendered in the > distance. Higher the multiplier values seem to cause more backdrop > text to disappear. (Nvidia doesn't seem to suffer from this value.) > (And FYI, if I disable the textures, the polygons still disappear on > the ATI, so unlike the first case, this does not seem related to > texturing.) > > So unfortunately, there doesn't seem to be a perfect value between the > artifacts and the missing polygons. After experimenting, I'm thinking, > I'm thinking 192 might be the best balance between the two. But I > think the range I'm looking at is 150-512. > > I am curious to hear what Mike sees for different values. > > But I'm thinking we might have to expose this value to a public API. > > Btw, my ATI card is an ATI Radeon 9800 Pro (chipset: ATY,R350). My > Nvidia card is a GeForce FX Go5200. Both are running OS X 10.4.7 > (PowerPC). > > Also, I did try disabling GL_DEPTH_TEST for the backdrop text just to > see what would happen. Both rendering problems did go away so I'm > pretty confident this is indeed a z-fighting problem. The unfortunate > side effect is the text doesn't get correctly culled or drawn when > below/ontop of the Earth model. > > So I'm thinking maybe in addition to a tweak API call, we might > want/need a render-method API tweak. Down the road we could introduce > this current render system (as default), a mode that disables > depth_test internally (for text that doesn't need to care about the > side effects), and a stencil buffer mode. > > Or I don't know if there is a bug report channel to get ATI to fix > this problem. We need to craft a good bug report to submit though. > > Thanks, > Eric _______________________________________________ osg-users mailing list [email protected] http://openscenegraph.net/mailman/listinfo/osg-users http://www.openscenegraph.org/
