Technical Information home | technical information | RMF format

hlfix currently performs three phases of geometry correction:

• Tesselating non-planar faces
• Decomposing non-convex solids
• Uniting coplanar faces

Tesselating non-planar faces

Figure 1.1 shows a brush with a non-planar face. Vertices 1, 2 and 3 of the face are in the indicated plane but vertex 4 is not.

Figure 1.1: Brush with non-planar face

• A "best-fit" normal is calculated for the face which comes close to the average normal of the intended surface
• The face is projected onto a plane with that normal, creating a 2D polygon
• The 2D polygon is triangulated using an ear-clipping algorithm. Ear-clipping involves removing the triangles formed by convex corners one by one until only a triangle remains.
• The original 3D face is tesselated with the equivelant triangulation
• Any resulting triangles that are adjacent and coplanar are ultimately united in a later phase.

Figure 1.2: Two possible tesselations of the face in figure 1.1

In order for this algorithm to work, the projected polygon must be a simple polygon. This means that its boundary cannot intersect itself. If the projected polygon is not simple, hlfix will abort with the error "Can't tesselate non-planar face". It's also important for the modeler to make sure that the tesselation of a non-planar face will not intersect other faces of the brush it's part of. This error will not be detected during the tesselation phase but will cause problems during later phases.

If two non-planar faces on two different brushes are coincident i.e. they share all of their edges, they will be tesselated the same way. This assures that tesselated brushes that touch each other will "fit" together snugly with no overlap or gaps.

Figure 1.3: Brush with many non-planar faces and it's tesselation

Decomposing non-convex solids

Figure 2.1 shows a non-convex brush. The highlighted edge is "reflex" meaning it points inwards.

Figure 2.1: Non-convex brush

hlfix eliminates reflex edges by cutting the brush along the plane of one of the faces adjacent to the edge, creating two or more new brushes. The plane that contains the most reflex edges is chosen for the cut. If the resulting brushes also contain reflex edges, the same procedure is used to cut them. This process continues recursively until all brushes are convex.

Figure 2.2: Decomposed brush

When a brush is cut, new faces must be generated in the cutting plane. hlfix does it's best to determine the texture information for these faces however this is not always possible. For example, the brush in figure 2.3 has two faces in the cutting plane but after decomposition, the corresponding surface area is covered by only one face.

Figure 2.3: The original brush has two faces (red and green) in the cutting plane.
These faces become a single face (purple) after decomposition.

In these cases, if the faces have different texture information, hlfix will give the warning "Found multiple textures for generated face"" and pick one of the textures randomly. To avoid this situation, don't put coplanar faces with different textures on the same brush unless you are certain that they won't be united in this way.

Uniting coplanar faces

At this point, all brushes are convex and so any coplanar faces on a brush must also be adjacent. Since the hlxxx compile tools don't allow this, hlfix simply unites all coplanar faces on a brush into a single face. If the faces being united don't all share the same texture information, hlfix will give the warning "Uniting faces with different texture info" and choose one of the textures at random.

Invalid input

hlfix may fail with solids that "pinch" i.e. the inner surface touches itself at any point. However, it's ok for the outer surface to touch itself. Figure 2.4 shows some examples of valid and invalid brushes.

Path support

hlfix will handle paths created with VHE's path tool and generate the proper entities when outputting to .map format. However, the custom node properties "speed", "yaw speed", "wait" and "wait for retrigger" are not supported. This is due to a bug in VHE which prevents these properties from being written to .rmf files. VHE currently does not export these fields to .map properly either so they are effectively useless whether you use hlfix or not.

VHE also does not generate ping-pong or circular paths properly, however hlfix does overcome this problem. You can safely use all three path types with hlfix.

Error messages

Message	Cause	Fix
WARNING: Uniting faces with different texture info	Two adjacent and coplanar faces on the same brush have different texture info	The brush must be manually split so that the offending textures are on separate brushes
WARNING: Found multiple textures for generated face	A face generated during decomposition contains multiple original faces with different texture info	The brush must be manually split so that the offending textures are on separate brushes
ERROR: Could not tesselate non-planar face	A non-planar face can't be triangulated probably because it's projection is not a simple polygon	Brush geometry is invalid and must be modified
ERROR: Attempt to assemble incomplete edge cycle	This error occurs during the decomposition phase and is normally the result of an invalid brush	Brush geometry is invalid and must be modified. If you believe your geometry is valid, this may be the result of a bug in hlfix.
ERROR: Inner edge cycle generated with no containing outer cycle	This error occurs during the decomposition phase and is normally the result of an invalid brush	Brush geometry is invalid and must be modified. If you believe your geometry is valid, this may be the result of a bug in hlfix.
ERROR: Orphaned face # [texture] with normal (# # #)	This error occurs during the decomposition phase and is normally the result of an invalid brush	Brush geometry is invalid and must be modified. If you believe your geometry is valid, this may be the result of a bug in hlfix.
ERROR: Incomplete solid	This error occurs during the decomposition phase and is normally the result of an invalid brush	Brush geometry is invalid and must be modified. If you believe your geometry is valid, this may be the result of a bug in hlfix.
ERROR: Attempt to cut outer/inner edge cycle which lies entirely within cutting plane	This error should never occur and is probably the result of a bug in hlfix
ERROR: Odd number of front/back intersection points	This error should never occur and is probably the result of a bug in hlfix