XSI: Quick and Easy LOD Levels

The example model I'll be using is that of the HL2 Combine model you can see on the right but I'll be treating it more like a static prop than an animated character through the tutorial. Its current triangle count is 3852 and I'll show you how we get that down to under 900 and still look like a combine soldier.

I'm using XSI Mod Tool version 7.5 and I'm assuming you already have some basic knowledge of the interface. I'll also be using the default layout so I don't lose anyone.

Now the actual tool/function that's used to help lower poly counts is called Polygon Reduction and can be found on the left menu under Modify > Poly. Mesh > Polygon Reduction

If you have your model selected and then use the Polygon Reduction function then it will apply the reduction to the entire model like so:

From a quick glance you can see that there are only 50% of the original polygons and it still resembles a combine soldier very well. However, applying the reduction to the entire model at once is only good once in a while - normally small reductions for the first few LOD levels.

What you really want to do is select the sections of the model you want to reduce piece by piece via the Raycast Selection or Rectangle Selection polygon options.

Now I'm just going to start again with the original model and show you some of the options you can do and use the hands as an example.

The default option is "Ratio Units" but just think of it as the 'Percent of Original' to remove. Quick and easy and all you have to do is move the slider up/down till your happy with the results.

Normally you will just use that, but in the event that you want to be extremely precise about the polycount on your models there are two more options that allow you to specify either the final vertex or triangle count. So if you wanted the hand to have just 40 polygons then you would just switch the mode from "Ratio" to "Final Triangle Count" and type in 40 like so:

To sum up the different reduction types:

With these basic tools you should now be able to easily modify your models to create several LOD levels and increase their performance in-game.

And like I said in the beginning, this tool is quite capable of taking that 3852 poly Combine soldier and turning it into a simple 900 poly Combine soldier with even more room to go lower with some spot touch-ups.

Just remember to export a new .smd file for each LOD level you want before you get too carried away as you should aim for a smooth transition from your most detailed model to the least detailed.

With your model selected just hit M and you should see your pointer change a bit along with some new buttons in the bottom centre of the screen:

It's the third button that you should be interested in at this point as that toggles the weld points option in which you can just click on a point and drag it to a neighbour and they will weld together. A small word of warning though about doing it this way, regularly freeze your model as after doing a dozen or so point welds your system will be using a lot of memory and be really slow. Trust me you'll notice when this happens so just hit the freeze button occasionally when working in this fashion.

A very simple qc file looks like this:

$modelname  "somefolder\model.mdl"
$body "body"    "model_ref.smd"
$staticprop
$surfaceprop    metal
$cdmaterials    "models\somefolder"


$sequence idle  "model_idle.smd" loop fps 15

$collisionmodel "model-phys.smd" 
{ 
     $concave
}

And to add in the various LOD smd files you've made there are a few simple lines to add:

$lod 5 //Distance from model in metres
{
      replacemodel "original.smd" "LOD_Replacement.smd"
}

You just cut/paste this little section for however many LOD smd's you've made for your model and change their distances:

$modelname    "somefolder\model.mdl"
$body "body"    "model_ref.smd"
$staticprop
$surfaceprop    metal
$cdmaterials    "models\somefolder"


$sequence idle  "model_idle.smd" loop fps 15

$collisionmodel "modelphys.smd" 
{ 
     $concave
}

$lod 5 //Distance from model in metres
{
      replacemodel "modelref.smd" "LODReplacement1.smd"
}
$lod 10 //Distance from model in metres
{
      replacemodel "modelref.smd" "LODReplacement2.smd"
}
$lod 15 //Distance from model in metres
{
      replacemodel "modelref.smd" "LODReplacement3.smd"
}

Now you'll have a rather simple optimized prop for use in your map. Keep in mind this example just deals with the basics, this tutorial should just be a stepping stone to more complex things. I would suggesting checking out the Valve Developer Wiki for more information and details about how to further control your models performance outside of basic static props as with the above qc file example.