Smoothing Groups

[Wilco]

okay i've got the basics of a model (and I mean basics ). But on a supposedly flat surface XSI renders a sharp contrasting line through it. Now from what I've read this has something to do with "smoothing groups", I can guess at how they work but I dont know where the option is in XSI. Can anyone explain how you use them?

 

[Wilco]

P.S.
While im here, can u get XSI to work with just Triangles? Like show all the edges and not hide them in polygons

 

[Jaenos]

I believe you are talking about discontinuity angle rather then subdivisional surfacing(hit the + or -, while it does fake subdividing it and smooths it, it's absolutely useless for games because it's basically adding twice the poly count)

Anyway, and someone can correct me if I am wrong here, to change the disconinuity angle;

1. Open the Explorer (hot key 8)

2. Branch down the object you want

3. Locate "Geometry Approximation" it will most likely be in italics, double click it.

4. Press Yes or No to the question you ask, depending on what you want

5. Locate the Poly Mesh Tab and go to it

6. There you will see the Discontinuity Angle set at the defaul 60, raise it to smooth, lower it to sharpen.


If all else fails, just play with the verts so it isn't so sharp.

Triangulation

1. Go to the "Model" side(the right hand buttons, press 1 for Modeling,2 for Animation, 3 for Rendering, 4 for Simulate)

2. Locate Modify>PolyMesh>Triangulate

As long as you have your mesh selected when you do that, bam, triangulated.

 

[Wilco]

that doesnt seem to solve what I mean....

heres some pics. the first 1 shows that the side of the object is flat, and the second 1 shows the wierd reflection thats coming off it

Front:

Side:

I dont know if this can be solved, or its its just what im doing. but it crops up later in wierder ways.

 

[Wilco]

also I cant find triangulate under Modify->Poly Mesh. Im using XSI EXP so im not sure if its in this.

sorry for the double posts but I do 1 thing, post, get 2 the next thing, and I cba to edit the prev 1

 

[Jaenos]

Oh, I think I see now, you are talking about the odd shading that is occuring on a flat polygon, not about sharp edges?

This is a common problem when I am working on half a character and have the other half cloned, on certain polygons it has the opposite perfered angle(since I just scale everything -1 to flip it) thus creating something like what I am seeing... if this is in fact your problem. The quick solution is to not use a quad; sometimes triangluation function(that you can't find, sorry I don't use exp) will select the prefered angle, yet it's still wrong, so you have to go in manually....

If you showed the wireframe of the second pic, this might be easier(if what I am talking about is your problem, hehehe) Anyway, just slice your quads into triangles, and try different ways, I am just going to guess at this one....

The black lines are the supposed wireframe(again just a simple guess work) and the red lines are what you should do, you will see that they go "against the grain" for your unwanted highlights, thus getting rid of them, in theory.

If I am completely wrong about your problem, sorry, heh

 

[spin]

If I understand the problem correctly, it looks like Jaenos took care of answering it. Turning that edge should take care of that smoothing error that he pointed out.

However, if you are talking about the very sharp line running across where the flat part of the body meets the area that starts to curve inwards, that is where two opposing smoothing groups meet. Like so:

Setting up smoothing groups that share edges will result in a hard edge as shown. Groups 1 and 2 share an edge, and groups 2 and 3 share another edge.

Note that I am using Max, but the theory is still the same. I don't know how XSI handles smoothing groups, but I can try to help you with it if this is indeed the problem you're referring to.

 

[Jaenos]

Ah I see, so if, in your example, the sphere was three different meshes it would result in that? Actually, I'd be interested in learning more about what you speak of, spin, so please continue.

 

[Wilco]

Okay here's a side wireframe pic.

as u can see theres no actual edge where the "line" is in the shaded view. If I add an edge there the shading goes away, but theres other places where adding edges doesnt seem 2 work XSI Help is fcking useless

 

[Jaenos]

XSI Help is actually really awesome, but I'm betting because you are using the exp addition it is useless, hehehe.

Anyway, did you try adding edges in the spots where you say it doesn't work in different combinations? Like I said, try against the grain so try different ways of splitting the poly.

 

[spin]

Sorry for taking so long to reply, but I've been having problems with my ISP. I have a response typed up in a text file that I'll paste here if this goes through.

Edit: Hmph, it won't go through for some reason. I'll try breaking it up.

Jaenos: That is a single mesh. Again, I've never used XSI, so I don't know how things are done with it. However, Max and Milkshape 3D use numbered smoothing groups. These groups can be applied to any faces on the mesh, resulting in only those selected being smoothed. When two smoothing groups meet each other and share an edge between them, you get a hard edged effect, as shown in the image from my post above. Here's another example.

That is all a single mesh object with different smoothing groups applied to random faces that I selected.

 

[spin]

Okay here's a side wireframe pic.

as u can see theres no actual edge where the "line" is in the shaded view. If I add an edge there the shading goes away, but theres other places where adding edges doesnt seem 2 work XSI Help is fcking useless

The edge actually exists there, it is just hidden. I don't know how XSI works since I don't use it, but I assume it works similarly to Max in handling visible and invisible edges. Creating a visible edge there seems to be manipulating the smoothing groups with unpredictable results. I really don't know what I'm talking about here in reguard to XSI, so I'll leave that one to someone that can answer correctly.

 

[Mr. Coffee]

Smoothing in XSI:

In XSI the entire mesh is smoothed out according to the Discontinuity Angle. If the normals between two adjacent polygons are within this angle, then their common edges are smoothed. This works well for an approximation, but some edges are bound to be wrong. For these cases you must specify them as hard or smooth (Modify -> Component -> Mark Hard Edge/Vertex).

In edge.jpg I’ve made a sphere equivalent to Spin’s using this method.

In gun.jpg is a possible solution to your problem. This will fix the smoothing error on the side of the rifle, but at the expense of a sharp transition between the polygons.