question about NewtonMeshAddFace usage

[sinisa]

Hi all,

I've been working on a fast-paced game for iPhone, using Newton for physics. Everything works great (very easy to use, works without any problems, congrats to developers on this one), except part when I want to use NewtonMesh to create collision, instead of Newton's box/sphere body. I need it because one model needs to have precise collision detection, and has some curved surface part.

Problem:

When I generate NewtonMesh, create a Convex Hull Collision based on that mesh, and then NewtonBody, bounding box of that body is significantly bigger than mesh's bounding box should be. I've read supporting vertices from newton's body (up/down/left/right/front/back) and rendered it in wireframe over actual 3d mesh to see what's going on, and wire box is huge. I've initially used code sample found somewhere on this forum. That sample was including vertex (smoothing) normals and texture coordinates (I have no idea why it was required for collision calculation).

I've changed code to what looked logical to me, and apparently it worked (now bounding box received back from NewtonBody is the same as the one loaded with real mesh, and body reacts on hits in a way I would expect it).

However, I'd like to check with Newton crew if this is how newton mesh was supposed to be generated, and also I have few more questions (below source code):

Code: Select all

   vec3f *data_verts = ddata->vertices; // ptr to array of vertices (vertices are glDrawElement ready, so 3 vertices in a row are 1 face)
   NewtonMesh *nwMesh = NewtonMeshCreate(); // allocate new newton mesh
   NewtonMeshBeginFace(nwMesh); // start adding faces
   xfloat verts[3*3];
   for( xint t = 0; t < trinum; t++) // for each triangle fill coordinates of 3 vertices (9 float values) ...
   {
      for( xint v = 0; v<3; v++)
      {
         verts[v*3+0] = data_verts[ t*3+v ].x;
         verts[v*3+1] = data_verts[ t*3+v  ].y;
         verts[v*3+2] = data_verts[ t*3+v  ].z;
      }
      NewtonMeshAddFace( nwMesh,3,verts,sizeof(xfloat)*3,0); // ...and add them to newton's mesh.
   }
   NewtonMeshEndFace(nwMesh);
   col = NewtonCreateConvexHullFromMesh(nwWorld, nwMesh, 0.1f, 0);
   body = NewtonCreateBody(nwWorld, col);
   ..... etc .....


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NewtonMeshBeginFace(nwMesh);

QUESTION: is this really needed? I've tried without begin/end function pair and it worked too. what is the purpose of begin/end functions?

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NewtonMeshAddFace( nwMesh,3,verts,sizeof(xfloat)*3,0);

QUESTION: why function 'add face' requires number of vertices? triangle has 3 vertices. is newton mesh able to load triangle fan instead? or multiple triangles with 1 function call? if so, is it better to pass to newton all triangles at once, or one-by-one? also, stride size is distance between vertex data (size of 1 vertex data), and in the case number of vertices is not 3, is this also affected?

Code: Select all

col = NewtonCreateConvexHullFromMesh(nwWorld, nwMesh, 0.1f, 0);

QUESTION: if mesh is already defined with triangles, how will 'tolerance' parameter in this function affect collision calculation?

Thanks in advance!
Cheers,

[JernejL]

Newton trimesh can happly support triangles, quads, and even more vertices per face, i assume newton mesh is same.

[sinisa]

Newton trimesh can happly support triangles, quads, and even more vertices per face, i assume newton mesh is same.

Thanx for prompt reply, however didn't answer my questions

[Stucuk]

Newton trimesh can happly support triangles, quads, and even more vertices per face, i assume newton mesh is same.

Thanx for prompt reply, however didn't answer my questions

What Delfi is saying is you can pass any Polygon shape as a face (As long as its Convex.. At least i think it has to be Convex. Never used NewtonMesh). So it works with all Polygon types rather than just Trianges.

[Julio Jerez]

the triangle of the mesh are not part of teh face of teh convex shape.

to tolerance is a parameter that is used for post processing of teh hull,
after a conevex hull is made, it takes each point point and calculate the average plane equation of the face formed by all the point that are directly conected too the center point.
then it calculate the distacne from the center point to the plane equation and if it is less than the tolerance, it means that point can be removed from the Hull.
It keeps doing that until no more points can be extracted while each time it removes a point, the Hull is repaired.
This have the effect that simplify convex hull where points are clustered too close

a value of 0.1 is probably too big,

[sinisa]

the triangle of the mesh are not part of teh face of teh convex shape.

to tolerance is a parameter that is used for post processing of teh hull,
after a conevex hull is made, it takes each point point and calculate the average plane equation of the face formed by all the point that are directly conected too the center point.
then it calculate the distacne from the center point to the plane equation and if it is less than the tolerance, it means that point can be removed from the Hull.
It keeps doing that until no more points can be extracted while each time it removes a point, the Hull is repaired.
This have the effect that simplify convex hull where points are clustered too close

a value of 0.1 is probably too big,

Thnx! ))