From: Paik, Charles C (Charles.Paik++at++MW.Boeing.com)
Date: 01/27/2000 07:06:46
Thanks for the responses thus far. I believe the best suggestions thus far
is to use an alpha blending approach. I have considered using alpha
blending. However, I believe alpha blending may give unwanted effects.
Let's take the example of rendering the scene with the first material
properties, and then turn on alpha blending and render the scene with the
second set of material properties. There would a problem with the second
render if there were objects that overlapped each other, and I would
definitely have things that would overlap. I have an earth-sky model, a
terrain model, and other models that populate the terrain. Each time an
object is rendered in a specific pixel, the alpha blending would blend it in
with the background pixel. So, I have the potential of blending in the
earth-sky model, terrain, and other models in a single pixel, but the effect
I want is to blend only the model with the background. I suppose I might
want to sort by distance, but I was hoping not to get to that low level of
control.
I welcome future comment Thanks.
-- Charles C. Paik The Boeing Company P.O. Box 516 MC S106-4715 St. Louis, MO 630166-0516email: charles.c.paik++at++boeing.com phone: 314-233-6807 fax: 314-232-4181
> ---------- > From: Lawrence Bertoldi[SMTP:lberto++at++bert.clubfed.sgi.com] > Sent: Wednesday, January 26, 2000 11:35 PM > To: Paik, Charles C > Cc: 'info-performer++at++sgi.com' > Subject: Re: Changing Accumulation Buffer > > > > Hi, > > > > I am rendering a scene with 2 different sets of material properties. I > > would like to display the scene as if the scene was rendered separately > and > > additively superimposed. My thought was that the accumulation buffer > would > > be ideal for this application. I could render each scene independently > and > > use the accumulation buffer to mix the imagery. However, it seems that > > there is a serious performance penalty with the accumulation buffer. > > > > I used an onyx2 at 1280x1024 resolution as a test bed. It seems that > it > > takes approximately 3.5 ms for each glAccum operation. In my > experiments, I > > would > > > > 1) Render the scene with the first material property to the color > buffer, > > 2) Copy the color buffer to the accumulation buffer, > > 3) Render the scene with the second material property to the color > buffer, > > 4) Additively transfer the color buffer to the accumulation buffer, and > > 5) Copy the accumulation buffer back to the color buffer. > > > Why not render the scene once with the first material to the color buffer > Then: > change the material, > then do something like > glBlendFunc(GL_CONSTANT_ALPHA_EXT,GL_ONE_MINUS_CONSTANT_ALPHA_EXT); > ( if no alpha (you might want to check the man page for > specifics)), > glBlendEquationEXT(GL_FUNC_ADD_EXT); > glEnable(GL_BLEND); > > render the object or scene again? > > > > > There are three transfers between the color and accumulation buffers > (Steps > > 2, 4, & 5). Those three steps have caused an additional 10.5 ms of fill > > time. 10.5 ms is a very heavy hit for my application. > > > > My next thought was to render the second scene directly in the > accumulation > > buffer, and additively transfer the accumulation buffer back to the > color > > buffer. But I do not know how to do either of those steps. (Or even if > it > > is possible.) > > > > Can anyone offer any suggestions? I am open to any hints, hacks, or > > altogether different approaches. Thanks. > > > > > > PS Does anyone know how to load tiff files in performer? Thanks again. > > -- > > Charles C. Paik > > The Boeing Company > > P.O. Box 516 MC S106-4715 > > St. Louis, MO 630166-0516 > > > > email: charles.c.paik++at++boeing.com > > phone: 314-233-6807 fax: 314-232-4181 > > ----------------------------------------------------------------------- > > List Archives, FAQ, FTP: http://www.sgi.com/software/performer/ > > Submissions: info-performer++at++sgi.com > > Admin. requests: info-performer-request++at++sgi.com > > > > Lawrence Eugene Bertoldi > graphics consultant > SGI Professional Services > ~;-}> >
This archive was generated by hypermail 2b29 : Thu Jan 27 2000 - 07:08:01 PST