6 replies to this topic

[enigma]

I must render the silhouette of an arbitrary 3D model.
The models are in OBJ format.
First I have follow this to read obj file:
http://cggmwww.csie..../2002/prog1.htm
It works, but only if in the file are stored vertex normals.
For example:

v -1.500976 13.063408 0.460043

vn -0.461797 0.858629 -0.222485

vt 0.000000 0.000000

But if the vertex normals are not stored in this manner, I'm not able to found a silhouette.
So, I have tried this code for read obj file:
http://www.gamedev.n...=12&gforum_id=0
(third post, objread.h).
Whit this code, vertex normal are manually generated.
It works, but with some problems, for example:

In this rendering, there are some wrong edges.
For me is because some normals are wrong. It's correct?
How can I solve this problem?
Thanks!!

[yakul]

I am not sure what you are trying to do.
But if you want a fast outline rendering, you should take a look at this:
http://graphics.cs.b...dges/index.html

[enigma]

Hi!
I've found and I tried to use this code:

void drawSilhouette(GLfloat r, GLfloat g, GLfloat b)

{

	glPolygonMode(GL_FRONT,GL_FILL);

	glDepthFunc(GL_LESS);

             glEnable(GL_CULL_FACE);


	glBegin(GL_TRIANGLES);

	glColor3f(0.0, 0.0,0.0);


	//Here I draw my model with GL_TRIANGLES


	glEnable(GL_BLEND);

	glBlendFunc(GL_SRC_ALPHA,GL_ONE_MINUS_SRC_ALPHA);


	glColor3f(r, g, b);

	glLineWidth(1.0);

	glDepthFunc(GL_LEQUAL);

	glPolygonMode(GL_BACK, GL_LINE);

	glCullFace(GL_FRONT);


	//Here I draw my model with GL_TRIANGLES


	glDisable(GL_BLEND);

	

	glDepthFunc(GL_LESS);

	glCullFace(GL_BACK);

	glDisable(GL_CULL_FACE);

}

It works correctly, see for example this silhouette rendering of Utah Teapot:

But I've a problem if the model has a holes, see for example this rendering of a head:

How can I fix this problem?
In the other cases the method run correctly!
Thanks!

[Mattias Gustavsson]

well, easiest way would be to fix the model, so it no longer has any holes :-)

[starstutter]

Mattias Gustavsson said:

well, easiest way would be to fix the model, so it no longer has any holes :-)

I hate to say it, but he's right. Your 3D models should never have holes in them.

[enigma]

starstutter said:

I hate to say it, but he's right. Your 3D models should never have holes in them.

Ok, no holes... :-)
Otherwise, in this case, I must use another method...
Thanks!

[Vilem Otte]

Well, you can render silhouettes with holes using pixel comparing and some value to compare when it's silhouette and when not, anyway it has to run as post processing effect in a pixel shader.