look at "Rendering Model" in chapter 16 of the programmer's reference. It briefly discusses the model for volume rendering, which is different from the rendering of surfaces. Opacity of 0 does not imply invisibility; to make something invisible it must have a color *value* of 0.
Think of the model as a cloud of little light emitters that can also absorb light. An opacity of 0 just means that that particular emitter doesn't absorb anything from the guys behind it. It still emits color. _________________________________ Donna L. Gresh, Ph.D. Visual Analysis Group IBM T.J. Watson Research Center (914) 784-5049 [EMAIL PROTECTED] Rasmus Bording <[EMAIL PROTECTED]>@opendx.watson.ibm.com on 04/06/2001 10:15:50 AM Please respond to [email protected] Sent by: [EMAIL PROTECTED] To: "[email protected]" <[email protected]> cc: Subject: [opendx-users] Volum render and opacities Hi! I am working on a volumdata set of a heart. It is a scalarfield over a tetrahedral grid. I use the built in volumrender in OpenDX to visualize it. A screencapture of the VPE in action looks like this: http://www.stud.ifi.uio.no/~rasmusb/hovedfag/dx/screen.jpg My question is, why are there red areas in the image? Since the opacety value for the red is 0, should'nt the red ares actually be black? To me it looks like the opacity table has no effect on the volumrender at all. Is this correct? Is the opacity table constant or something when using the volum render? The net and datafile for the example are available here: http://www.stud.ifi.uio.no/~rasmusb/hovedfag/dx/ -- Rasmus Bording [EMAIL PROTECTED] http://www.bording.no/rasmus "In the beginning the Universe was created. This however has made many people very angry and has been widely regarded as a bad move." -Douglas N. Adams
