MDL normals

void R_BuildFrameNormals (aliashdr_t *hdr, trivertx_t *verts, dtriangle_t *triangles, vertexnormals_t *vnorms)
{
	for (int i = 0; i < hdr->numverts; i++)
	{
		// no normals initially
		Vector3Clear (vnorms[i].normal);
		vnorms[i].numnormals = 0;
	}

	for (int i = 0; i < hdr->numtris; i++)
	{
		float triverts[3][3];
		float vtemp1[3], vtemp2[3], normal[3];
		int *vertindexes = triangles[i].vertindex;

		// undo the vertex rotation from modelgen.c here too
		for (int j = 0; j < 3; j++)
		{
			triverts[j][0] = (float) verts[vertindexes[j]].v[1] * hdr->scale[1] + hdr->scale_origin[1];
			triverts[j][1] = -((float) verts[vertindexes[j]].v[0] * hdr->scale[0] + hdr->scale_origin[0]);
			triverts[j][2] = (float) verts[vertindexes[j]].v[2] * hdr->scale[2] + hdr->scale_origin[2];
		}

		// calc the per-triangle normal
		Vector3Subtract (vtemp1, triverts[0], triverts[1]);
		Vector3Subtract (vtemp2, triverts[2], triverts[1]);
		Vector3Cross (normal, vtemp1, vtemp2);
		Vector3Normalize (normal);

		// rotate the normal so the model faces down the positive x axis
		float newnormal[3] = {-normal[1], normal[0], normal[2]};

		// and accumulate it into the calculated normals array
		for (int j = 0; j < 3; j++)
		{
			Vector3Add (vnorms[vertindexes[j]].normal, vnorms[vertindexes[j]].normal, newnormal);
			vnorms[vertindexes[j]].numnormals++;
		}
	}

	// copy out normals
	for (int i = 0; i < hdr->numverts; i++)
	{
		// numnormals was checked for > 0 in modelgen.c so we shouldn't need to do it again
		// here but we do anyway just in case a rogue modder has used a bad modelling tool
		if (vnorms[i].numnormals > 0)
		{
			Vector3Scalef (vnorms[i].normal, vnorms[i].normal, (float) vnorms[i].numnormals);
			Vector3Normalize (vnorms[i].normal);
		}
		else Vector3Set (vnorms[i].normal, 0.0f, 0.0f, 1.0f);
	}
}