Re: Transparent Layering w/ Solids

*To*: mathgroup at smc.vnet.net*Subject*: [mg26561] Re: Transparent Layering w/ Solids*From*: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>*Date*: Fri, 5 Jan 2001 22:22:58 -0500 (EST)*Organization*: Universitaet Leipzig*References*: <92k1b0$636@smc.vnet.net> <92uru4$dt3@smc.vnet.net> <933mqg$k9r@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Hi Martin, thanks for this nice solution. > Of course, this is far from being as powerful as OpenGL-like > transparency > (whatever that might be :-). something like ? http://phong.informatik.uni-leipzig.de/~kuska/mathgl3dv3/09296d70.jpg MathGL3d "transparence" uses alpha-Blending for transprent polygons. It draw the polygons from back to front and combine the pixels in the frame buffer due to alpha*PolygonPixelColor+(1-alpha)*OldPixelColor with and alpha<1 the polygon look transparent. OpenGL has two problems with it. At first, the depth buffer does not work for transparent objects. Drawing the polygons in a false order (not back to front) some artefacts become visible. MathGL3d sort the transparent polygons and draw all transparent polygons after the solid objects in the graphics. Since the sorting can take some time, only for new view points the polygon order is updated. Using the spin option of MathGL3d with transparent objects may fail. Reordering can be forced by using the viewpoint control and select the synchron update of the main window. The second problem here is that the human eye not only expect transparence, it expect light refraction too. Because every real transparent object must have a refraction index differnt form 1. This can't be simulated with OpenGL and for good looking transparent objects a raytracer is the only possible solution. Fortunatly MathGL3d can write POVRay scripts and it is easy to add a refraction index to the scripts and get real looking transparent objects. Regards Jens