Chat Log: Env mapping in detail

Listed in: Technical backgrounds
Date: 2000-05-29
Author: ali
13:01 Antimorph: Laser I have a question for you
13:02 Antimorph: On some custom cars I've downloaded, every face of the model is reflecting light oddly
13:02 LaserBeams: hrm?
13:02 LaserBeams: like - examples?
13:02 Antimorph: hmm, cant think of one, let me rephrase
13:02 Antimorph: how do you control the glossiness on cars?
13:03 LaserBeams: in the parameters.txt
13:03 Antimorph: hmm, ok, for the car your working on with ST, you mentioned that you were going to make the fenders reflect differently from the body
13:03 LaserBeams: yes
13:04 Antimorph: how is such a thing achieved?
13:04 LaserBeams: the vertex normals will not be matched there
13:04 LaserBeams: you mean in max?
13:04 Antimorph: yes please
13:04 LaserBeams: I have not a clue - I know how to do it in Rhino...
13:05 Antimorph: What do you do in Rhino?
13:05 LaserBeams: weld wherever you want the reflections to flow smoothly across body
13:05 Antimorph: weld vertices?
13:05 LaserBeams: do not weld where you want reflection "creases" - yes
13:05 Antimorph: kewl
13:05 LaserBeams: if it looks smooth in perspective, the reflection will be smooth
13:06 LaserBeams: if it looks faceted, the reflection will be faceted
13:06 Antimorph: thankyou, I was having an epi fit wondering if it was something to do with smoothing groups, but I thought that couldn't be
13:06 LaserBeams: It does
13:06 LaserBeams: want to know how it eorks?
13:06 LaserBeams: works?
13:06 Antimorph: yes please
13:07 LaserBeams: Expl follows...
13:07 LaserBeams: Each model has a list of vertexes and vertex normals
13:08 LaserBeams: each polygon is defined by indexing into that list of vertices
13:09 LaserBeams: flat surfaces have normals that point straight (perpendicularly) away from the face
13:09 LaserBeams: When two vertexes are blended, their normals are averaged
13:09 LaserBeams: and converted into one vertex, with one normal
13:10 LaserBeams: the polygons that used the previous two vertexes
13:10 LaserBeams: both now index onto the one, blended vertex
13:10 Antimorph: I understand Laser
13:10 LaserBeams: this is used in gouraud shading to approximate curved surfaces
13:11 LaserBeams: the normals are used to calculate reflections
13:11 Antimorph: So how do you blend your vertices then?
13:11 LaserBeams: weld
13:11 Antimorph: ok, nothing to do with SG's then
13:11 LaserBeams: I guess not - though maybe
13:12 LaserBeams: if it makes it look smooth, then yes.
13:12 Antimorph: hmm
13:13 Antimorph is concerned
13:13 LaserBeams: If the normal is pointing directly at the camera, the coordinate at the center of the env map is set to that point on the secondary texture
13:14 LaserBeams: if the normal is pointing directly away from the camera, a point around the edge of a circular area from the env map is set to that point on the secondary texture
13:14 Antimorph: I need to go into max and take a look at this
13:15 Antimorph: be back in a bit
13:15 LaserBeams: normals pointing perpenicular tot he camera are refernced to a point halfway between the center of the env map and the circle inscribed in the env map.
13:15 Antimorph starts to sweat
13:16 SKITCH2: see ya later peeps
13:16 LaserBeams: normals between parallel and perpendicular are calulated with trigonometric functions so the enfironment appears spherical and not squarish

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