Antony Ward shows you how to optimise your polygon count to improve speed and response without making too many visual sacrifices

FOR: Maya

TOPICS COVERED:

• Level of detail principles
• Reducing polygon counts
• Simulating detail

Building assets for games is a bit like packing a case for a long holiday – there’s never enough room to fit everything in. Put too much on screen at the same time and the game can grind to a halt. This is where level of detail (LOD) models can help. By switching to lower-resolution models as the character or object moves away from the camera, you can lighten the overall polygon count on the screen without sacrificing visual quality. In this tutorial, Antony Ward shows you how to get the best out of LOD models while keeping quality high and the frame rate solid.

01 The golden rule
There’s one rule that all level of detail models must live by: the total number of polygons in the lower LODs must not be greater than the polygon count of the highest LOD. For example, if you’re using four LODs and your most detailed model has a total of 5,000 polygons, the next LOD down should be around 3,000, the model after that would be 1,500, and the last one would be 500. If you have more than four LODs, the limits would have to be adjusted.

TOP TIP: Switch to lower-resolution models as your character moves further away from the camera

The further away a model appears to be, the fewer polygons it needs to have

02 Remember to zoom out
It’s important to remember that the in-game model you’re working on won’t be seen until it’s a certain distance away from the camera. The player will never get up close, so, as you work, make sure you’re zooming out all the time. This way you can better judge what can be sacrificed, and what can’t. Viewing a lower LOD up close will always give you a false sense of how it will look in-game.

As characters get smaller, gradually reduce their hands to mitten shapes

03 Hack away at the hands
Hands are an obvious place to chop out those polygons – they typically hold a lot and the digits are relatively small. Initially, reduce the round digits until they’re more of a diamond shape and then start to sacrifice them – not by deleting them, but by merging the fingers gradually until you end up with a basic mitten shape.

At a distance you won’t see eyes blink or a mouth smile, so you can afford to chop these right back

04 Facial animation
If your model has facial animation, this is another area to sacrifice. At a distance you won’t see eyes blink or a mouth smile, so chop this right back, but leave room for the jaw to open and close so some degree of animation is still available to the medium LODs. If using blend shapes or morph targets, simply ensure these are disabled.

05 Remove small details
At a distance from the camera and surrounded by a complex game environment, small details on your model’s surface just won’t be seen. Items such as buttons, belts or buckles can easily be removed and, if needed, you can always replace them by painting them back in on the texture page.

06 Remove small tangents
When you’re optimising a model, you should look out for geometry that doesn’t add to the overall shape, or help in deformation. The same rules can apply to LOD models. When reducing, look out for slight tangents in its silhouette that won’t be missed if flattened.

07 If it’s quicker, rebuild
If you’re working with a high-res model, reducing it manually can be a tedious task – so why not just rebuild the model? Use the high-res version as a reference and, once built, adjust its UVs to fit the existing texture page or bake the texture from the high-res model down onto your new set.

Swap out an object and replace it with a simpler model with an alpha map applied

08 Use alpha maps
A quick way to claw back some of those precious polygons is to replace an object with a much simpler model, with an alpha map applied. This is an essential approach for curved or round objects, such as wheels. Reducing the geometry alone would result in a boxy-looking model, but adding an alpha plane at either side is quick, painless and can keep the object looking round.

09 Watch those texture seams
It’s all very well chopping out polygons here and there, but it will also affect your UV seams. You may find that when you remove a complete edge ring you’re left with a glaring seam. Depending on the LOD you’re working on, this may not be an issue as it will be too far away to even notice, but try to adjust the UVs, or update the texture page as you go.

10 Fill out the shape
Things become reduced when you take something away from them. As you peel away the geometry of your character models, you may notice that the body and limbs are much thinner than when you started. To avoid this rapid weight loss, keep comparing the shape against the highest LOD. A good trick is to put the higher LOD into a display layer and set it to Reference. This will display just its wireframe, so you can refer to it as you work.

In Maya you could use the Transfer Maps tool to bake textures onto the lower LODs

11 Bake textures down
If the budget will allow it, and you’re struggling with texture warping and UV seams, you can always use a smaller texture page for your LODs. Once the model has been reduced, rework the UVs and then bake the diffuse map down onto the lower LODs. In Maya use the Transfer Maps tool.

12 Skeleton LODs
Polygons take up memory, as do the joints moving them around. It’s not always a good idea to completely replace a skeleton on the fly, but you could reduce its influence on the model. So, for example, on lower LODs where you’ve reduced the hands, make sure you remove the finger joints’ influences too. The same applies to facial animation.

13 Minimise the ‘pop’ factor
When playing a game you can always tell when LOD models have swapped because you see that tell-tale ‘pop’. The character will suddenly, and often drastically, change shape as the higher LOD is removed and its lower replacement is loaded. You may not be able to completely avoid this, but you can make it less obvious by constantly comparing it with its higher version and using reduction techniques.

14 Strip out texture passes
It’s not just polygons and joints that can be removed: you can also strip out textures, particularly extra texture passes such as a normal map, reflection or specular pass, which would only be effective on the higher LODs.

Use a Level of Detail group to hide and reveal objects at different distances

15 Use a LOD group
As you create your LODs you’ll naturally want to see that they change at the correct distances. Maya has a handy tool to help: going to Edit > Level Of Detail > Group will put your objects into groups, which you can then show and hide when at specific distances from the camera. This is a great way to help reduce the ‘pop’ effect mentioned earlier. As an added bonus, some game engines will take this group and use the information in-game, so you know what you see is what will be in the game.

16 Stagger your LODs
If your model is made up from a collection of parts – like a vehicle, for example – then you don’t need to restrict yourself to just three or four set distances for objects to switch at. For instance, if the vehicle will be viewed from behind for most of the time, set the front elements to drop to lower LODs earlier than those behind.

Lower-poly models can suffer if the normals aren’t set up properly

17 Surface normals
Lower-poly geometry, when not using a normal map, can suffer if the normals aren’t set up correctly. You may end up with edges appearing darker than they should be and a general reduction in quality as the models swap. When you’ve reached your desired polygon limit, make sure you also do a normals pass, softening and hardening key edges to reduce this effect.

Keep an eye out for quads being triangulated the wrong way on lower models when exported

18 Triangulate and flip edges
When exported, most models are triangulated as part of the process, and on higher-resolution models the result is generally fine. On lower-end models, however, you can suffer when a quad is triangulated the wrong way so that the surface appears concave, rather than convex. To prevent this, make sure you triangulate any suspicious areas, ensuring the edges will export how you want them to and not how the exporter thinks they should be.

About the author
Antony Ward has been developing games since the early 1990s. He’s worked for some of today’s top game studios and has also written three books and numerous tutorials
www.ant-online.co.uk

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With tools like Unity 3D and markets like the App Store and Steam, building indie games is becoming easier and more lucrative. As a result, more and more indie games are being developed every single day.

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By Antony Ward

Modelling characters for games means knowing what to put in and what to leave out

For this sequence of tips, I hope to share some of the tricks and techniques I have learned in my 17 years in the games industry, with particular reference to modelling games characters at lower resolutions.

You may think this is redundant, and are possibly saying to yourself: “Surely I just use the first division from my sculpted model?” Or perhaps you’re glancing favourably at your re-topology tools.

These are all great starting points, but can only get you so far.

Besides, what if you are working with a model that isn’t pre-sculpted, or perhaps is aimed for a mobile device?

For those times, and many more, I hope these simple rules will help you as you work.

01 Know your restrictions

One of the first things you should investigate before starting any game character is your set of working restrictions.

By this I don’t mean polygon and texture page limits – which are paramount to the success of your creation, of course – but rather the environment settings and how the character will be used and seen in the game.

Environment settings are variables such as working units. Are you going to work in centimetres or metres? This has to remain consistent throughout the game or you will end up with scale issues further down the line, especially when rigging and animation are involved.

Knowing how the character will be used and what they must be able to do can have a dramatic effect on the model itself.

Will it be animated, for example? If so, will individual fingers need to bend, or will the mouth need to open? If the character wears a hat, will you ever see underneath it? If not, there’s little point in building the top of its head.

02 Do your research

Approaching a project with no research material is like building something with your eyes closed. Even the most talented artists have a wealth of reference around them while they work.

Working from memory is fine, but a folder of photographs or a wall of concept sketches to work from are crucial.

I often get asked to review work. It always surprises me, especially when recreating the human form, how many artists don’t use reference photos – or have them but aren’t applying them correctly. All it takes is an hour on the web and you can have some great images to guide you.

03 Start simple

When you start working on your character, don’t rush in and try to create a fully detailed head or hand: this can come later. Block out the whole figure first using basic primitives and stitch them together. I personally like to start by using cylinders.

This will give you a broad overview of the character’s proportions, and an immediate feel for how it will look. As an added bonus, this rough shape can be passed on to be rigged, and an animator can start blocking out some early moves.

04 Try subdivision surfaces

A fantastic way to create a smoother model with an initially low polygon count is to use subdivision surfaces. This method enables you to create a higher-detail model from a low-resolution ‘cage’ mesh, meaning you don’t need to push around lots of geometry.

Once you’re happy with your creation, you can simply bake out the model and convert it to a fully polygon-based mesh, ready for further editing and optimisation.

05 Add detail only where it’s needed

Many artists’ first impulse is to put detail into every area of their creation. It’s only natural to want to do your best, and produce an amazing character. But in the gaming world, it may just be a wasted effort if it’s never seen.

You need to know how the character will be used. If it will be seen from a distance, there’s no point adding fabric detail or the inside of its mouth. You could even use mitten-style hands if each individual finger will not be seen.

Zoom out as you work, to view the character as it would be seen.

06 Be economical

When the words Xbox 360 or PS3 are muttered, artists sometimes think, or are told, that polygon counts can go out of the window. I have worked on many projects where the artwork started out like this, only to then be greeted by a slideshow instead of a game, meaning work has to be redone.

Being economical and optimising models correctly can save you having to revisit your work later – and your lead artist will love you for it.

For me, two basic rules apply. First, remove all unseen geometry: if you can’t see it, delete it. Second, remove all unused geometry: anything which doesn’t directly benefit the shape of an object, or how it deforms.

A good example is a cube: it should only ever be made up of 12 triangles. Any added divisions are a pure waste unless they add to the shape.

07 Follow natural muscle lines

As you build, keep thinking ahead. As your character moves around in the virtual world, it will look better and deform in a more convincing way if your topology mimics the natural muscle layout of a real person.

You don’t need every muscle etching into the surface, however: the normal map, if you can use one, will add nice detail for you. Think of this more as the foundations of how the model will move.

If done correctly, when the arm raises the upper arm and shoulder, geometry will twist and crease as real muscles do.

08 Retain a seamless model

Having lots of separate elements added to a model can make it a pain to rig. As it deforms and moves around the screen, many parts will intersect with the main model, shattering the gaming experience.

This is also true of clothing. Creating the body beneath the outfit is never a good idea: always try and make the two elements part of a single model, or the skin under the clothing will inevitably pop through when the model is animated.

Physically building these into the mesh can stop this from happening, and make life easier for the animator.

09 Keep your topology clean

One phenomenon that bugs me more than any other is messy topology.

Being handed a model with random edges and vertices placed across the surface not only looks awful, but makes any future tasks more difficult, and more than often means the model has to be rebuilt or edited.

Remove anything that isn’t directly needed by the model and won’t enhance the way it looks or deforms.

Also move around the mesh and look for areas that aren’t tidy. Try to keep a clean, grid-type layout across the surface, and everyone will be happy.

10 Check deforming areas

Make sure you have enough geometry in areas that will deform. Not having the correct topology around an elbow, for example, will cause it to look jagged and harsh. It could even result in the elbow pinching as it bends.

You can get away with adding just a few extra polygons to avoid this, but keep the direction a joint will bend in mind. In the example of an elbow, add more around the outer elbow itself, as this will be the area that will stretch.

The inner elbow will also need attention, but will not require as much extra geometry. If you’re not sure, add a few joints and test it to see how it looks.

11 Image planes

Working from reference on your desk or on a second monitor is a good way to start, but why not bring these images into the application, so you can work on top of them and be more accurate?

All 3D applications have the ability to import image files so you can view them in the scene.

12 Work smarter, not harder

As a character modeller, you will work your way through many humans and creatures in your career, so why not make things easier for yourself?

If you create a good hand model with correct topology, for example, put it to one side so you can use it again on another character.

If the character design you’re working on is symmetrical, just model half and mirror it.

13 Keep your scene clean

When you work in games, your work is never your own. Once your character is modelled,
it will go through the hands of many other people before it gets into the game – so aim to keep your scene as tidy as possible.

Correctly name each model, delete unused nodes and shaders, and bake any construction history on your models. Leave the scene as you would like to be given it.

14 Unify your normals

Most geometry in your scene is set by default to be displayed as double-sided. This can cause confusion when things start to look strange, or that hard edge just won’t go away.

Chances are the normals are flipped on part of your model, so turn it to single-sided to highlight any potential problems.

15 Let the normal map help

Normal maps are great, so take full advantage of them. They add fantastic surface detail to any model, so if you can accomplish the same effect with a normal map, remove the polygons.

This is great for objects close to the surface, like a sock, jewellery or skin detail like tendons and veins.

16 Prioritise

Think about what will be seen most in your model, and prioritise the polygon budget accordingly.

If the character has a big hat, for example, spend more polygons rounding it off so it looks smooth.

If the character’s face will feature greatly, spend time making it look great.

17 Keep regular, sequential back-ups

Like us, your software and hardware have their bad days. Some days you sail through your modelling; the next you are fighting against crash after crash, with hours of work being lost. It sounds obvious, but save regularly and use your application’s auto-save function if it has one.

You can also set many apps to save sequentially, so if you make a mistake, you can roll back to a previous version.

18 Check the silhouette

Sometimes it’s difficult to step back and see a character with fresh eyes, especially if you’ve been working on it for a week. A quick test to help weed out those jagged, polygonal areas is to disable the lights in your scene.

This will leave you with a silhouette you can move around, making more obvious any areas in need of smoothing out.

Issue 146 of 3D World includes a free DVD. Click on the image for details of the latest issue

This month, 3D World is carrying a DVD rammed full of great stuff for you to try – including 13 hours of video!

Issue 146 goes on sale on 26th July in the UK (a month later in the US), so make sure you get your copy at the newsstand, subscribe today or buy a single issue.

Note: the digital Zino editions will not come with this content!

Geomagic Wrap trial (PC only) and video
Geomagic Wrap is an application that takes LIDAR data and generate a mesh, which you can then use as a 3D asset. We got a trial version of the app, some LIDAR data and a tutorial video by Craig Crane on how to use it. If you’ve ver wondered what you can do with a LIDAR set-up, now’s your chance to find out.

DAZ Studio 4 (PC and Mac, worth $49.95)
The latest edition of DAZ’s figure creation software provides access to the new Genesis line of figures. After the end of August DAZ Studio 4 will be $49.95 – so here it is for you, complete with a code to register the new Autofit feature.

DAZ models (worth $104)
We have collection of six items of DAZ clothing that works with the new Autofit feature in DAZ Studio 4.

LightWave 10.1 trial (PC and Mac), assets and video
With CORE technology being ported into the LightWave 10 series, here’s your chance to sample the new interactive preview renderer VPR, stereoscopic toolset, data interchange, linear colour workflow and FiberFX hair and fur system. We’ve also got rigged models for you to play with (check out the multithreaded mesh evaluation) and the opening chapter of Lino Grande’s DVD on rigging in LightWave.

Sculptris Alpha 6
If you’ve been unable to register or download the new sculpting tool from Pixologic, then we’ve got installs for both Mac and PC on the disc.

Substance Player (PC only)
Allegorithmic’s unique procedural texture generator is on the disc, alongside a sample set of Substances. A similar collection of textures would sell for about $120 online.

Digital-Tutors Photoshop video
This complete 104-minute series from Digital-Tutors shows how to take a typical character render and give it some visual oomph, ready to add to your portfolio.

InfiniteSkills Learning Maya 2012 video
This sample chapter of the InfiniteSkills video shows what to expect from the full 13-hour series on learning Maya 2012.

Bluebrain models (worth $314)
Bluebrain has supplied us with a detailed human skull, a Lamborghini Gallardo and an electronic cash till, all textured and ready to use in your own scenes.

Intero Visuals models (worth $550)
Intero has provided various home furnishings including a bed, table football, wall unit, chairs, tables and a jug – again, beautifully detailed and ready to populate your arch-viz interiors.

My3DTextures textures
This issue’s selection of textures includes concrete, fabric, foliage, grass, metal, rock, wheels and wood.

Soundsnap sound effects (worth $59)
Another set of useful sound effects, consisting of ambient backgrounds and various sound effects in addition to long and short music loops.

Tutorial files and videos
The disc also contains all the scene files and video you need to complete our Q&As and tutorials, including hard-surface modelling in Maya, sculpting clothes in 3ds max and ZBrush, an intro to Sculptris, files for the Cinema 4D tutorial, plus a video on subdivision surface modelling.

The range of models includes a copying machine, fan, air conditioner, desk chair and desk lamp.

Formats:

*.max (Scanline)
*.max (MentalRay)
*.max (Vray)
*.c4d Cinema4D
*.c4d Cinema 4D VRay
*.fbx
*.obj

Specification

Total size: 645MB
Materials: Yes
Textures: Yes

The collection is currently priced at $79.99. For more information and to see all the included models, visit the CGAxis website.