The first thing we have to do for our SDRVOD is get the body model. Since we're basing it on the existing Boogey Van (one of the trucks that came with the game), we shall be using a copy of it.
If you were to look for the Boogey Van models, you'd find that there are in fact three different .BIN files - Boogey.bin, Boogey0.bin and Boogey1.bin. The composite image below gives a comparative look at these different models:
The different models are used for different levels of detail. When the model is close to the viewer, you will be able to see the details on it - but when it's far away, you won't be able to see it and it would be a waste of computing power trying to draw it, and could cause unnecessary lag in the game. So what the game does is alternate between different models whenever it gets closer to the viewer or further away.
Boogey.bin has 184 vertices and 176 faces. You can see from the 3D solid view that it has a more complex surface structure than the other two. This is the high-detail model, and is used when the model is close enough for you to see the details on it. Boogey1.bin is the medium-detail model, with 160 vertices and 157 faces. It looks a little rough, but it's only used when the truck is a moderate distance away, so you won't notice the blemishes. Boogey0.bin is the low detail model, with a slimline 148 vertices and 151 faces. For both the textured and solid views it looks a right dog's breakfast, but this model is only used when the truck is so far away that, while you can still see it, it's impossible to pick up the details.
Using these different models, game performance can be improved by swapping in a model with lower detail and displaying the high-detail version(s) only when necessary. This takes a load off the CPU, so the game will run faster. This is standard fare with pretty much all 3D games these days.
For these reasons, most people do not make medium and low detail versions of their models, concentrating entirely on the single high detail model (the good looking one!). However the convention is that a good modeller will always strive to get the maximum face, texture, and vertex "effeciency" and not unnecessarily load a model up with detail.
You may have heard people complain of latency or "lag" in a game - when a game's framerate is so low that things happening on the screen do not move smoothly but appear to jerk or "chug". This usually occurs when too many things happen in the game at once, and your computer is struggling to keep up. The act of showing a 3-dimensional model such as an MTM2 truck moving around in a 3-dimensional environment such as an MTM2 track places a huge strain on the processor of a computer. As modern technology has evolved, computers have become faster and better able to cope with huge loads, so that the computing power required for an old game such as MTM2 has become paltry. But for an older, slower computer, framerates can really suffer when the computer tries to display a high-detail model moving and interacting with its environment.
As a general rule, the more detailed a model is, the more computing power is required to display it and make it appear to move. For a truck maker, this means that the more detail you pour into your truck, the more strain you are going to place on a computer trying to display it. This is an important consideration if you plan to release your truck to the world even if you do not have a slow computer yourself, because if a person with a slow computer tries to drive your truck they may find that their framerate plunges to unacceptably slow levels. You will notice that the stock trucks (the ones that come with the game) do not have terribly detailed bodies - they're solid, rather than having the detail of the fiberglass truck I describe here. The game developers have "considered the lowest denominator" with these: they may not look as fancy, but they allow for a decent framerate even with a computer that can only just run the game.
Three factors affect the amount of lag a detailed truck model produces on a computer: in order of importance, these are the number of vertices, the number of texture files, and the number of faces.
The number of vertices is the biggest factor - the more vertices a model has, the more computing power is required to project them into the 3D environment of the game. High vertice models - those that exceed 1000 vertices - can really make a huge drain on the game's framerate. Hence the reason why the stock trucks have a modest vertice count of around 200. A good rule of thumb is to try to stick to below 1000 vertices when making trucks, as this allows a decent amount of detail but still makes the truck run acceptabley on almost any system capable of running the game. Aim to be frugal with the number of vertices on your models.
The number of texture files also has an impact, because the game has to load these and hold them in memory to display the truck. You will need a large number of texture files to notice any difference, but practically speaking, you shouldn't need more than three for most types of truck.
The number of faces is the third factor that effects framerates, and it might be surprising to know that they don't really effect it much at all. It seems that vertices have the greatest effect by far, and projecting the faces that the truck uses is simple. As long as you are concious of the number of vertices you are using and use them efficiently, you can still build very detailed models that run beautifully in the game.
Of course, some 3D cards (especially the really new ones) can handle models way over 1000 verts, and some old ones have a limit much less than 1000 verts, but it is generally accepted that most are limited to exactly 1000. This means that when you make a truck you have to be mindful of this limit if you plan to have shiny faces on the truck.
It is possible to drive a truck whose model is over 1000 verts on a computer whose 3D card has the 1000 vert limit, if the faces of the model are set to MTM1 non-shiny texture. This basically eliminates the need for environment mapping. There are two ways to set it this way:
1) Turn "Truck reflections" in MTM2's 3D graphics options OFF.
2) Set the faces to 0x18 Normal Texture (MTM) type in BINedit.