3ds loader .. calc normals with multiple vertices used?!
Author
hi
i got an loader for 3ds files in openGL
an it works nearly perfect, ok ,there
are no NORMAL's saved in 3ds file format
i GOOGELD a lot of things with
"+opengl +calculating +normals etc
and i found some examples of calculatin face normal,
ok,but there is one mistake in it
when calculatin round objects like tree
there are points that should have a normal
direction mixed because that point is used
by some faces (sorry for my english,i normally speak only german)
for example this are 8 faces and 8 points (watching from top)
<img src="http://img111.imageshack.us/img111/4395/normal3df.jpg" alt="problem" />
when calculating point '0' with '2' and '3' they miss '6' and '7'
normally the normal of 0 must look North and not northeast like
here
what formula is there to combine all vertices
that are mutiple used by faces
(please no google answers anymore)
First off: 3ds files do support normals.
Second: Learn to use google. :D
If you want to calculate the "average" normal for those points..
1) calculate the normals of ALL faces that is connected to one vertex. (simple cross-product..)
2) Average those (should be depending on the area of the face) and you have your normal.
For a cube, you normally want "hard" edges, that is, no shared normals, but to use the face-normals instead, which means you have to split each vertex into 3 vertcies...
Good luck!
Second: Learn to use google. :D
If you want to calculate the "average" normal for those points..
1) calculate the normals of ALL faces that is connected to one vertex. (simple cross-product..)
2) Average those (should be depending on the area of the face) and you have your normal.
For a cube, you normally want "hard" edges, that is, no shared normals, but to use the face-normals instead, which means you have to split each vertex into 3 vertcies...
Good luck!
Author
chunk
0x4110 == vertices
chunk
0x4120 == face polys
chunk
0x4140: == texture coordinates
etc..etc
google tell not about the mistery what chunk
uses/stores normals but it looks that
YOU "gugli" know more about it :)
please feel free to tell us more about it here
or did anybody else know a complete serious describtion of .3ds files
with "normal" definitions inside..so i can stop thinking about normals
when using 3d editors (only watching face orientation when creating objects)
a lot of "google" result tells that 3ds did NOT store normals
set the normal for the vertex to be the average face normal for all the triangles that use the vertex. this will look "right" and will provide smoother shading than having the vertex have a different normal for each triangle that uses it.
-me
for ( each vertex ){ find all the triangles that use it; for (each triangle) { add the tri normal to the average; } normalize the average;}-me
Quote:Original post by Palidine
set the normal for the vertex to be the average face normal for all the triangles that use the vertex. this will look "right" and will provide smoother shading than having the vertex have a different normal for each triangle that uses it.for ( each vertex ){ find all the triangles that use it; for (each triangle) { add the tri normal to the average; } normalize the average;}
-me
Agree. In addition, I've just written a basic 3ds loader (tell me if you want the source to look at, and I could mail it to you, if you're interested) and AFAIK there are no normals stored in the 3ds format file. Most of the others formats I looked at don't keep normals simply because they can be calculated from vertices. Only a couple of formats do that (but I don't remember wich).
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