View Full Version : Transparency maps VS fog and reflections

09-15-2003, 05:45 PM
This is my first post, please be gentle...

When making landscapes and cities that need lots of trees in the scene, I use a single square polygon with a photo of a tree as the texture map, and a BW high contrast of the same tree as the alpha mask. Pretty basic concept, I suppose, and it works great, it even casts raytraced shadows. Problem is when reflected in shiny windows and doors, and if there is any distance fog in the scene, the alpha mask doesn't seem to work. But I think I remember it working a few years ago in LW5.6, I currently use 7.0.

09-16-2003, 12:50 PM
I'm not sure this will solve your current issue but
anyway insure your black and white map (alpha) should be
used as CLIP MAP texture and in no case as TRANSPARENT texture.
Leave your transparent texture alone (0% transparency),
open the Object properties panel, tab "render" and check CLIP MAP,
then you'll see you can apply your alpha map the same way than
you first did in the surface editor.

1/ generally it solves troubles like you seem to have
2/ rendering is 10 x more fast
3/ don't forget though that clip mapping works as YES or NO,
means that levels of greys in your image won't be recognize and
it will only be 100% opaque or 100% transparent.
That said I don't think your image has too many levels of greys according
to what you're doing with it (tree shape).
Clip Mapping is always better for such things, transparency map is
usefull only is precisely you need different levels of transparency…

Oh, about your trouble it may come from the fact
you have or not enabled the Ray Trace Transparency in the rendering options
window, try both and see if one works better than the other…

09-23-2003, 10:22 AM
Thanks, lasco!

Your solution worked wonders. I really appreciate the help.

09-25-2003, 03:51 PM
every time you need to cut off a part of geometry from rendering you must use clip map, be cause it cut off geometry.
render engine see the hole, and not transparency.

it's more fast be cause not check transparency and not calculate diffraction, refraction and other thing of transparency.

it's more stable be cause work with every kind of shadow (ray trace shadow and shadow map).

if you find some jagg on edge (clip map read only white and black, cut or not cut surface, gray is used like white if is more than 50% limous, like black if is less than 50%)
you can try with a more high resolution image or you can apply the clip image on transparency channel of surface, it blend the edge correctly, and with clip you not risk the problem of single transparency map.

don't miss that clip map are saved with scene and not with obj.
have a nice day.