Wrong Polygon indices

[fraukman2]

Hi everyone, I'm writing a small ray tracer, and I'm having problems with the mesh indices, the order is wrong.

for(int i = 0;i < meshes.size();i++)
			{
				for (int k = 0; k < meshes[i].PolyCount;k++)
				{
					Int32 indexPointA = meshes[i].indices[k].a;
					Int32 indexPointB = meshes[i].indices[k].b;
					Int32 indexPointC = meshes[i].indices[k].c;
					
					Tri triangle;
					triangle.vertex0 = (meshes[i].vertices[indexPointA]) / 100.0f;
					triangle.vertex1 = (meshes[i].vertices[indexPointB]) / 100.0f;
					triangle.vertex2 = (meshes[i].vertices[indexPointC]) / 100.0f;
					IntersectTri(ray, triangle);
					if (ray.t < 1e30f)
					{
						_film->setImagePixel(x, y, 255, 255, 255);
					}
				}
			}

I'm using a plane (previously triangulated) to test and get this result:

i debuged the indices and they are wrong.
indices:
{1,3,0} - triangle 1
{1,2,3} - triangle 2

this is how i get the polygons:

void Scene::_recurseHierarchy(BaseObject* op)
	{
		while (op)
		{
			Bool isPolygon = op->IsInstanceOf(Opolygon) && !op->IsInstanceOf(Ojoint);
			if (isPolygon)
			{
				Frog::Mesh mesh = {};
				GePrint(op->GetName());

				PolygonObject* poly = (PolygonObject*)op;
				if (poly)
				{
					Int32 numOfVertices = poly->GetPointCount();
					const CPolygon* cpoly = poly->GetPolygonR();
					CPolygon* trianguled = nullptr;
					const Vector* vetices = poly->GetPointR();
					Int32 trianguledPolyCount;
					Bool triRes = Triangulate(vetices, numOfVertices, &trianguled, &trianguledPolyCount);
					if (triRes)
					{
						mesh.vertices = vetices;
						mesh.indices = trianguled;
						mesh.PolyCount = trianguledPolyCount;
						objects.push_back(mesh);
					}
				}
			}
			_recurseHierarchy(op->GetDown());
			op = op->GetNext();
		}
	}

Can anyone point me what I'm doing wrong ?

[m_adam]

Hi @fraukman2 thanks for posting, for me it's looks like a bug, since if you use a polygon primitive instead of a plane, it work as expected. I think there is a remapping needed for the point indices and polygon indices but I don't get it.

As it is the Christmas season, some members of the development team are away and the answer to this question may take longer than usual.
But I will keep you posted as soon as I have more information.

In the meantime, the easiest way would be to use MCOMMAND_TRIAGULATE that will triangulate the passed object.

BaseObject* op = doc->GetActiveObject();
if (!op)
	return true;

// This will triangle op, if you dont want to affect the object in the scene call GetClone first.
PolygonObject* poly = static_cast<PolygonObject*>(op);

ModelingCommandData mcd; 
mcd.op = op;
if (!SendModelingCommand(MCOMMAND_TRIANGULATE, mcd)) 
	return false;

EventAdd();
return true;

Cheers,
Maxime.

[fraukman2]

Hi @m_adam, I just tested your suggestion and worked flawless, thank you very much.

Cheers and happy holidays