Game Character Creation Series: Kila Chapter 10 - Level of Detail Variations

Final product image — What You'll Be Creating

Well, it had to happen eventually, but we have reached the final part of the Game Character Creation Series. We have had fun over the previous nine tutorials, and hopefully you have learned a lot, but even though this is the last in this series it’s still a crucial part of the real time character building process.

Throughout this course we have talked in detail about optimization. Whether that was geometry, texture size or even joint limits, we have always had restrictions to work within to maintain an economical and game friendly model and rig.

In Part 10 we will take model optimization to the next level as we look at making Kila even more efficient when she is viewed at any distance. To do this we will need to be harsh and strip her down to her base geometry, reducing her to mere shapes and colors as we create her various level of detail models.

What are LODs?

Every game, be it for a high end PC, a console like the Playstation 4, or even aimed at the more modest mobile market will utilize level of detail models. These models are simply lower resolution versions of the main character, prop or vehicle which are swapped in as they move away from the game camera.

If we take Kila as an example. She currently weighs in at around 10,700 polygons, which is quite modest by some of today’s standards. This is fine as she is close to the camera, but as she moves into the distance you lose most of her details as she occupies fewer pixels on screen. The problem is, the game engine will still be processing most of the geometry. Take the rest of the environment into account, plus non player characters, vehicles and particle effects and the processor starts to quickly reach its limits.

In order for things to run smoothly you need to keep an eye on the overall polygon count, so to do this, Level of Detail models or LODs for short, are used.

As Kila walks into the distance she seamlessly swaps from her 10,700 polygon model down to a lighter 7,000 polygon version. This then eventually changes to a 3,000 polygon model, and continues to drop through each version until she simply can’t be seen. If done correctly you may not even notice.

Watch as you play any game and you will see this happening as the character, (or vehicle, or prop) suddenly pops as the models swap to a lower, boxier version.

1. Creating Your LODs

There are various approaches to creating level of detail models. Some more advanced systems are code based, meaning that the model is dynamically reduced by the game engine at set distances. Others are a little more involved with the artists’ 3D application having a built in “reduce” option to do some of the work for you, although in practice these often leave the artist with more clean-up work to do.

There are even stand along applications which will optimize the geometry for you and output the various resolutions, ready to use.

In this tutorial you will be going back to basics and taking a much more traditional, hands on approach which means you can be in full control of just what is removed from where. This means you can ensure deforming areas work correctly, at any distance, and you can also strive to avoid the dreaded and sometimes obvious LOD pop mentioned earlier.

With the approach decided the next question you should be asking is what are the target polygon limits for each model? Ideally, to remain economical, the total polygon count of all your LODs shouldn’t exceed that of the main model.

If Kila is 10,700 polygons then you should be looking at the following limits.

LOD 1 – 10,700
LOD 2 – 7,000
LOD 3 – 3,000
LOD 4 – 450

So all the lower level of detail models add up to 10,450 which is below the polygon count on the highest, allowing for a little wiggle room should you need it.

Step 1: LOD Preparation

So where do you begin with Kila?

You have the main model which is the primary LOD. This is good for use when she is closer to the camera as she has all the major details so you can move your focus onto the second level of detail.

Begin by loading Kila_LOD_Start.ma.
Now rename the model of Kila to Kila_LOD01_10666, which shows which LOD it is, and the current polygon count. Feel free to adjust this to match your own polygon count if it differs.

Initially you will need a copy of this model to work upon, but as she is currently rigged you need to make sure the duplicate is in the default pose. This is so each new version you create has an identical pose, meaning they all match and line up with the rig when you come to reattach them to the skeleton.

Go to Modify > Evaluate Nodes > Ignore All.
Now select the Kila_LOD01_10666 model.
Go to Skin > Go To Bind Pose.

You should notice the head move slightly, which is exactly what you were looking for.

Now duplicate the Kila model and rename this to Kila_LOD02_7k so you know which level of detail it is you are working on, and the desired polygon count.
You can now hide everything else in the scene so you can focus on just this model.

Note: You might also need to unlock the models attributes if you want to move, rotate, or scale her.

Tip: To work in a safer environment why not delete the rig and save this scene separately. You can always import all the LODs back into the rigged scene once you are finished.

2. LOD 02 – 7,000 Polygons

Now you have the first duplicate you are ready to start working, but before you do it’s beneficial to visualize roughly how this 7,000 polygon level of detail will be seen in game.

To do this simply zoom out slightly, so she is roughly half the size, as demonstrated in the image below.

It’s a basic step but it’s crucial to see the model like this so you know exactly which details can be removed as they simply aren’t seen at this distance.

Spend some time now examining Kila while keeping her at a distance. Rotate around her and look at what can be sacrificed.

There will be plenty of obvious places you should spot straight away, but remember that this LOD also needs to remain as close to the original as possible, with no drastic reduction happening at this stage. This will help to reduce the amount of LOD pop as the models swap.

Now you have examined the model for a while you can zoom back in and start chipping away at the polygon count, removing enough geometry to reach your 7,000 polygon goal.

Obvious places which just can’t be seen at the target distance should go first, but then the focus should shift to topology. Tiny polygons and ones which don’t add greatly to the volume of the model should be deleted next, as should any geometry which is essentially hidden.

Note: You must always keep in mind that areas which need to deform, like her face, knees, elbows etc. will still need to at the target distance, so don`t remove too much geometry from those areas at this stage.

Let’s work through some key areas to focus on.

Note: In this tutorial we won’t be walking through the removal of each and every polygon. Instead we will focus on key areas to work on to give you the general idea.

The first area to remove would be her eyelashes. These are relatively quite small, and from the test distance not really noticeable.
Next you should reduce her inner mouth elements, so in this case that would be her teeth and tongue. At the target distance you won`t see every tooth so this is a good place to chop out a good amount of geometry.

Step 1: Head Reduction

Densely populated areas, like the face and hands should be the next area to work on but, as mentioned, you do need to be careful as they will still need to deform convincingly.

At this level you are simply looking to reduce hidden geometry, or small polygons. So with the head you can safely work on her scalp and ears which are hidden by her hair for most of the time.

Note: The best workflow for reducing textured models is to use the Edge Collapse, or Delete Edge tools. This will remove the geometry while also maintaining the UV layout.

With her face, try to find smaller geometry and follow edge loops and rings to keep the topology clean. Her lips and around her cheeks can easily be optimized here, with little noticeable effect.
Kila's eyes can also be simplified. The main eyeball can be reduced, and her iris can also be less rounded, again, you won`t tell the difference at the target distance.
Finally move onto her hair and strip out any dense edge loops over her scalp.

Tip: Remember to use the Isolate Selected tool to quickly hide areas you aren't working on. This is a great way to focus on the eyes, or just the head without the rest of the model being in your way.

Step 2: Hand Reduction

The hands are next to work on. You will see that there is a lot of extra topology in each finger which only adds to the shape in a slight way. This is mostly over each knuckle which helps the fingers to bend, and between each knuckle along the fingers length which adds a slight bulge.

Go in and remove these now by simply selecting the edge loops and deleting the edges.
You can then focus on the back of the hand and the palm, removing a full edge ring which flows around the hand.
While you’re here you might as well chop some geometry out of her bracelet too.

Step 3: Foot & Lower Leg Reduction

Moving on you can now drop to the lower end of her body and look at Kila's feet. Again, looking at them you can see you added lots of extra geometry to round off her shoes and reduce the jaggedness of the model, this can now all be trimmed away.

If you look around the side of the trainers, above and below the red stripe, you will see a slight bevel. This is so small that at a distance it won't be seen. Perfect to remove!
You can also work around the circumference of her footwear, collapsing every other edge ring. Close up it will look more angular, but from a set distance it looks no different.

What you will find now is since you removed geometry from around the outside of the trainer, the upper part seems almost out of balance. It’s this effect which will happen frequently as you work. One area will be reduced, and in doing so another will suddenly become an obvious candidate for optimization.

Continue to reduce the upper trainer, and feel free to follow the natural flow of your work onto her lower, and then upper legs.

Note: When reducing the geometry on any model with normal maps you may notice that the resulting area may not appear as smooth as the original. Areas may also appear darker, but don't worry about this now as we will look into a quick way to combat this later in the tutorial.

Step 4: Torso Reduction

We have looked at Kila's extremities so it’s time to now focus on her core. There is plenty you can remove from her torso, and in doing so should highlight other areas to work on.

The chest is an obvious candidate for reduction. This area has lots of smaller polygons simply because in the original model needed a nice curve in its silhouette.

A good place to start with the chest is to collapse alternate horizontal edge rings. This will quickly half the amount of geometry here.
If you stay on the shirt, the rim around the bottom can also be collapsed. It’s quite slim so again, won't be seen at a distance.
You can then focus on her stomach and shoulders, removing an edge ring initially before zooming out to see if you can afford to collapse any more.

Note: Keep an eye on your UV seams and make sure you correct the UVs if the model is altered in a dramatic, and noticeable way.

While working on the front of her torso you will inadvertently end up editing her back. As you select and collapse edge rings, they obviously flow around the whole model, saving you time in the long run.

However, there is more you can do.

Originally, geometry was added to Kila to enhance the creases in her shirt. These are prime for removal as they only add a slight hint of detail at a distance.
The upper section of her jeans can be reduced. The edge ring around the center only adds a little curvature here which works up close, but won't make a difference on this LOD.
You can also remove the bevel which adds a lip to the lower part of the same section.
Finally, the curvature of her buttocks could cope with losing a horizontal edge ring or two.

Now those key areas have been reduced continue to work around the model, collapsing and deleting more edges until you reach your 7,000 polygon goal. Remember you are looking for hidden geometry, small polygons or edges which don't add greatly to the volume of the character.

If you aren't confident make sure you zoom out to the target distance before and after you remove the geometry. At the end of the day, if something doesn't work you can always hit Undo!

With the first pass complete you can see that once zoomed out there is little, if any noticeable difference between the two levels of detail.

Ideally you want to zoom out and let Maya automatically swap the models for you so you can visualize just how close they are. This is something we will look at later in the tutorial.

Tip: Don't worry if you haven't reached you target polygon count. If you feel like you are getting to a stage where you can’t see many more geometry to remove then leave this model and start to work on the next. You can always come back to this one later.

3. LOD 03 – 3,000 Polygons

The first LOD is complete, or at the very least you have taken a huge chunk off the polygon count and intend to revisit it later.

For the next level of detail you follow exactly the same process, except you duplicate LOD 2, rather than the main model to give you your starting point. The good news is that you have less geometry to play with, plus this version is further away from the camera, so you can afford to be a bit more aggressive with your polygon removal.

Duplicate Kila_LOD02_7k and rename this to Kila_LOD03_3k.
Hide the other models in the scene and focus on the new duplicate.
Again, begin by zooming out so this LOD is half the size of the previous so you can visualize how it will be seen in game.

You are further away now, and at a point where her eyes are just a few pixels in size. It’s this that you need to keep in mind as you work because it’s easy when your close up to keep small details which aren't needed.

Tip: As you’re working on this lower LOD, keep an eye out for extra ways in which you can remove more from the previous LOD if you need to go back to it.

So, the process begins again, exactly as you did before except you can be less conservative.