convex hull v.s. user mesh

[Neo]

Hey, I'm just building newton system in my irrlicht map...and I need to make everything (excloding the floor) in my map into dynamic body.
but the thing is, for a little bit more complex object, for example a wall with an arch door in it, the convex hull seems not a ideal choise,it turns out that
the collision which the function createConvexHull provided would be a wall with no arch door(I saw this in the sandbox)...

another option is to make the objects into usermesh or treecollision, however, they are static bodies. Any other idea? Thx

[Julio Jerez]

you can separate the arch and use NewtonMeshApproximateConvexDecomposition to make into a compound, check out ConvexApproximation.cpp in teh sandbox

[Neo]

you can separate the arch and use NewtonMeshApproximateConvexDecomposition to make into a compound, check out ConvexApproximation.cpp in teh sandbox

Thx, but there comes a new problem: My meshes are extracted from the irrlicht scene, and I'm quite sure that irrlicht mesh has different archetecture with the newton mesh joint.
So, because I cannot load mesh directly from .ngd file like the sdkdome did, I want to extract the vertices and faces from the irrlicht mesh(like what I did in building tree collision and convexhull collision), and somehow rebuild a newton mesh with them.
I've tried to use NewtonMeshAddFace to create the newton mesh, but it turned out totally in a mess...
So any ideas? Did I use the mesh joint functions in a right way?

[Neo]

here is the code:

Code: Select all

NewtonBody* mapManager::createMeshConvexHull(NewtonWorld* nWorld, scene::IMeshSceneNode* irr_meshNode, s32 shapeID,bool sync,scene::IMesh*irrmesh)
{
   //Function to create a NewtonMeshCollision from irrlicht mesh
   scene::IMesh *mesh;
   if(sync)mesh=static_cast<scene::IMeshSceneNode*>(irr_meshNode)->getMesh();//if the scene node is the mesh source, extract the mesh
   else mesh=irrmesh;//load external mesh

   NewtonMesh*cMesh=NewtonMeshCreate(nWorld);

   NewtonMeshBeginFace(cMesh);
   u32 nMeshBuffer=0;//total count of the meshBuffer
   u32 vertice_index[3]={0,0,0};//vertex index
   scene::IMeshBuffer *mesh_buffer=NULL;
   f32 vertex_array[33];//vertex array（a newtonmesh node has 11 values
   //they are vertice（vertex_array[0]~vertex_array[3]）、normal（vertex_array[4]~vertex_array[6]）、and uv coordinates（vertex_array[7]~vertex_array[10]））
   //as a collison，all we need is the first 4 values, plus the 4th value(w axis) has to be set to 0.

   for (nMeshBuffer=0;nMeshBuffer<mesh->getMeshBufferCount();nMeshBuffer++)
   {
      mesh_buffer=mesh->getMeshBuffer(nMeshBuffer);
      //get node and index pointer
      video::S3DVertex *vertices=(video::S3DVertex*)mesh_buffer->getVertices();
      u16*indices=mesh_buffer->getIndices();

      //fill the collision model
      for (u32 i=0;i<mesh_buffer->getIndexCount();i+=3)
      {
         //extract 3 node one time
         for(u32 j=0;j<3;j++)vertice_index[j]=indices[i+j];

         //first
         vertex_array[0]=vertices[vertice_index[0]].Pos.X;
         vertex_array[1]=vertices[vertice_index[0]].Pos.Y;
         vertex_array[2]=vertices[vertice_index[0]].Pos.Z;
         vertex_array[4]=0.0f;
         //second
         vertex_array[11]=vertices[vertice_index[1]].Pos.X;
         vertex_array[12]=vertices[vertice_index[1]].Pos.Y;
         vertex_array[13]=vertices[vertice_index[1]].Pos.Z;
         vertex_array[14]=0.0f;
         //third
         vertex_array[21]=vertices[vertice_index[2]].Pos.X;
         vertex_array[22]=vertices[vertice_index[2]].Pos.Y;
         vertex_array[23]=vertices[vertice_index[2]].Pos.Z;
         vertex_array[24]=0.0f;


         //add new face to newtonMesh
         NewtonMeshAddFace(cMesh,//destination model
            3,//total vertices for one face
            &vertex_array[0],//vertex array
            11*sizeof(f32),//the bit size of one node
            0);//material ID（no need here）
      }
   }

   NewtonMeshEndFace(cMesh);

   NewtonMesh* const convexApproximation=NewtonMeshApproximateConvexDecomposition(cMesh,0.01f,0.02f,64,200,NULL);
   NewtonCollision* const compoundC=NewtonCreateCompoundCollisionFromMesh(nWorld,convexApproximation,0.001f,shapeID,0);
   
   vector3df scale=irr_meshNode->getScale()*IrrToNewton;//irrToNewton is set to 0.1, I use this value for simulation purpose
   vector3df pos=irr_meshNode->getPosition()*IrrToNewton;
   NewtonCollisionSetScale(compoundC,scale.X,scale.Y,scale.Z);//scale the collision
   matrix4 matrix;
   matrix.makeIdentity();
   matrix.setTranslation(pos);//set the position of the newtonBody
   NewtonBody* mb=NewtonCreateBody(nWorld,compoundC,&matrix.pointer()[0]);
   
   NewtonMeshDestroy(cMesh);
   NewtonMeshDestroy(convexApproximation);
   NewtonDestroyCollision(compoundC);
   return mb;
}


[Julio Jerez]

you need to cinver the mesh to a NewtonMesh, by makeing one and adding the faces to it.

[Neo]

you need to cinver the mesh to a NewtonMesh, by makeing one and adding the faces to it.

I did...as above...but it turns out that collision mesh in scene is totally a huge....stuff...I cannot even tell want is it...it's not like the original mesh at all...just messy faces stick together...
I just wonder what's wrong with my function(see above)?