Creating Valid Geometry for Level exporting on trueSpace/gameSpace.
by Rodrigo Hernández (Kwizatz)

Introduction

Lots of people ask about why they can't just export the game levels they have made on gameSpace or trueSpace successfully, and many more have doubts about what makes an object (called a brush on BSP terminology) legal or illegal - this tutorial will try to explain those things, and will show you some techniques to help you create valid brushes. The tutorial is written from the point of view of using the Aeon Games Mapper plug-in, though some of the points about what makes geometry legal and illegal will apply in general to level exporting with any plug-in.

So, what makes a brush illegal?

An object, block, or brush (I will refer to these just as brushes from now on) is considered illegal if it has more than 32 faces or more than 16 edges, if its concave or if it has 2 or more coplanar faces, I will explain those characteristics in detail.

No more than 32 faces?

A face, simply put is any of the flat surfaces on a brush, for example in a cube each side of the cube would be a face, a face can also be defined as any of the polygons (a 2D shape) that form a polyhedron (a 3d shape), notice that since the "smallest" polygon you can draw is a triangle, in the cube example above you can have 2 faces (if you split each square into 2 triangles) per side, but we will leave that for later, for now just understand what a face is .

You can see here the visible faces of a cube marked with black lines:

By right clicking the Object Tool in trueSpace/gameSpace you will get the Object Info window, there you will be able to see how many faces does your brush has:

Here you can see that the Cube has 6 faces, and now that you know what a face is and how to find out how many faces a brush has, all that you need to do is keep the count under 32 for any given object.

No more than 16 edges?

Now that you know what a face is , it will be easy for you to understand what an edge is, and edge, if you have not figured it out already, is each one of the straight lines that delimit the face, in our picture of the cube each straight black line is an edge.

On this image I have highlighted each edge with a different color, so its easy to spot them.

And now that you know what an edge is, you know that you cant have more than 16 of them on each brush, there is no easy way to know how many edges there are in a brush in trueSpace/gameSpace, or at least not that I know off, but the Mapper can easily spot if there are more than 16 edges in an object and it will report it, so you can fix it.

Concave?

Brushes MUST be convex, a polygon is convex if it doesn't have any dents, and its concave if it does have dents, a classic example is Pac-Man, when the yellow dude opens his mouth he is concave, when he closes it, he is convex, here are some examples, excuse the bad drawing skills :

Now, in 3D there is no concave or convex per se, so the way to tell if a brush is convex or concave is to check its faces, if all faces represent convex polygons, the brush is said to be convex, if at least one face is concave, the brush is said to be concave and hence, invalid. There is no way to tell if a brush is concave in trueSpace/gameSpace other than eyeballing it, but luckily again, the Mapper is able to spot them and report the problems.

So, that's it, you just have to avoid concave faces.

Coplanar faces?

Two faces are said to be coplanar if they reside on the same imaginary plane, remember I said we would leave the problem for having 2 faces per cube side?, well now its the time.

When you triangulate a cube, you will get 2 triangles per side, each of those triangles is coplanar in respect to the other, because they are in the same plane.

This cube if triangulated like that, will be no good for exporting, the solution is to remove the edges between the coplanar faces, you can do this manually or use the "Remove Edges" tool found on the Mapper.

The way to find out if a face is coplanar to another is to compare their normals, if two faces have the same normal (or are between the acceptable range to consider them the same), and they are adjacent to one another (they share and edge), they are said to be coplanar.

Now that you know what a coplanar face is, you can avoid them too .

Let's get to Work!

Now that you know what to avoid when modeling a level in trueSpace or gameSpace, I am going to teach you some techniques you can use to make your levels export at the first try. Now, of course this is focused on exporting using the Mapper, however the techniques should apply to pretty much any other level exporter.

We will be building a door's frame or arc, initially I was thinking about just a plain tube, but that was too easy and boring, so I think this will be a lot more fun. We won't get into texturing, because first, it would make the tutorial way too long, and second, I will be explaining texturing on a different tutorial, so we will pick up texturing then. Finally, I will be adding a door to the frame, but inside the game the door would not be functional unless you set it as a door entity or somehow you program its behavior on your own, if exported just as a brush (as we will be doing here) the door will only work as decoration.

Enough babble, fire up your trueSpace or gameSpace environment and proceed to Step 1:

Step 1:
Start by creating a simple cylinder with the cylinder () tool:

Step 2:
Bring up the Object info window and set the "Location" to 0,0,0 so the cylinder sits nicely right at the center of the scene, leave the size on 2,2,2 meters, we will be using meters because that's what I use, and most game engines measure distances in meters, feel free to change to whatever suits your preference, but keep in mind that this is a door frame, keep it big enough to allow a person to pass thru.

Step 3:
Create a new cylinder and set the location to 0,0,0 as well, but this time set the size to 1.5,1.5,3.0.

The 1.5 values represent the actual width of the door, the 3 is just so the second cylinder extends quite a bit over and under the first cylinder because we will be applying a boolean on step 4.

Step 4:
Select the first cylinder and click the Boolean subtract tool (), the default parameters for the boolean are ok, but if you want to change then right click the tool to do so, we will be changing those later, for now leave them as they are.

Click the second cylinder, you will get the following result:

if you get something different, perhaps you forgot to select the first cylinder before applying the boolean subtraction, hopefully, you should be able to Undo and try again.

Step 5:
Having selected the resulting polyhedron, press the triangulate tool (), switch to the top view () and zoom a bit to you get a better picture of the donut :

Step 6:
Go into point edit and using the Rectangle Selection tool ( ) select half the tube as shown below, make sure you have Backside checked on the selection parameters, if you are not sure and you can't find the window, just right click the Rectangle Selection tool and the window will pop up.

Step 7:
Still in point edit mode, press the Separate selected part of object tool (), this will split the tube in two, press delete, we don't need the lower half of the tube, you will end up with something like this:

Step 8:
Change back to Perspective View (), go into point edit mode and select the two faces generated by the split, as you can see here:

Step 9:
Go back again to the Top View () and press the Sweep tool (), our frame starts to get some shape:

Step 10:
Still in point edit mode and having the 2 faces selected, bring up the object info window, and click somewhere in the window, anywhere, so the object info fills with the data for the selected faces and not the whole object. Change the Location Y value (which should be 0.500 if you have faithfully followed my instructions) to say 2.000.

Note that you could had just used the bounding box widget to drag the surfaces down, that's completely valid, and if you prefer to do it that way its fine, however this way we get tidy numbers instead of something like say 1.987, notice how nicely the shape fits on the grid too.

Step 11:
Ok, the arch is done, but we now need to break the geometry so it is completely valid, right now, this wont even export, so start by hitting delete so the selection is dropped, then using rectangular selection (still inside point edit mode), select one of the columns of our arch as follows:

And then just press the Separate selected part of object tool (), that will effectively break the geometry in 2 pieces, the column and the rest of our arc, remember to have the backside check for the selection tool, otherwise you would only select the face facing you, and you won't get the desired results.

Step 12:
Now everything else left to do is pretty much repeat the last step on all convex chunks you can find, try to split the geometry always by the biggest convex piece there is, that way you will end up with less brushes and the engine will have an easier time doing its calculations, for example, we could proceed to break each single triangle shaped block, but that would give us twice the number of required blocks, so, instead select each rhomboid shaped block as shown here:

And press the Separate selected part of object tool .

Step 13:
Once you are done splitting the arch around, you should end with the arch split like this:

I have given different colors to each block so you can notice that they are now indeed different blocks, there is still one problem to be solved before we can export the arch, and that is, the coplanar faces on the rhomboid brushes.

© 2003-2004 Rodrigo Hernández All Rights Reserved