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HappyDay's blog


Car tire model explained

posted Monday, 12 May 2014 by FS HappyDay
Welcome everybody to my blog. In this blog I will mainly talk about level design, modeling, texture creation and any other creative work I do while working on Urban Terror HD. Why? Because I like to show off work that I'm proud of. :)

When working on a map I usually start with the things that give me the most joy working on and I procrastinate doing the boring work, even if that's what actually should be done first. So in my first blog entry I'll show you screenshots of one of the first models I created for Urt HD and I'll explain a bit how I did it. If you have no experience in level design this might give you a glimpse of how the environments in games are created. If you are a mapper you might learn some new technique. In any case I hope you'll enjoy reading this post.

When creating a game asset I always start with a high poly model that has tons of detail. I use blender as my 3D application of choice but 3ds Max or Maya are just as good (those two are actually the industry standard). You can see the high poly version of a car tire I modeled on the very left on the two images below. The first screenshot shows the models in solid mode, the second one shows the wireframe. As you can see, all of the detail is actually in the model, there is no texture used on the high poly model, just a basic black color. In case you didn't know, game engines break down surfaces into triangles (tris for short) no matter what shape the surface initially has. The more tris your graphics card has to render, the lower your fps (frames per second) will be. 64740 tris is obviously too much to be used in a real time game for such a simple object. In current UrT maps somewhere around 20k - 50k tris are drawn at any given time for the whole map (!). So, since the high poly model is far too complex to be used as is, lower resolution models have to be used and much of the detail has to be faked by textures.

A series of low poly models labeled lod 0 - lod 2 (lod = level of detail) are actually used in the game. The lod 0 model is used when you are very close to the model. The further away you get, the smaller the object will be on your screen and the less detail you will be able to see. That's why the lod 0 model automatically gets replaced by a lower detail lod 1 model at a certain distance. If done correctly you won't even be able to see the switch happening. In theory any number of lods can be used but at some point it's not worth the effort to create them or it's not even possible to reduce the tris anymore. In this case I used three different lod models.


Now let's talk about getting the detail of the high poly model onto the low poly models. That's the job of the textures. Each model uses several different textures which are more or less important. The image below shows the three main textures I use for the tire model. The base color map (also called diffuse map) defines, like the name suggests, the color of the model. I created this texture with the free version of dDo, an awesome photoshop add-on that makes it so easy to create amazing textures for your models. The ambient occlusion map and normal map are generated in blender from the high poly model in a process called "baking". All of the detail of the high poly model is baked to a texture that can be used on a low poly model. The ambient occlusion map fakes the darker, more concealed areas of the model, whereas the normal map shows the direction the surfaces are facing in the world. The latter information is used to make light and shadow behave as if there was all this detail in the model. The textures play such an important role in how realistic an object looks, they almost work like magic :) . Having explained this, take another look at the first image and note how you can hardly see any difference between the high poly model and lod 0. All the lod models use the ambient occlusion map and normal map generated from the high poly model.

You might have wondered what the collision model in the first two images is all about. Determining where a player can walk and where his path is blocked is computationally a very expensive task. Poor collision has an even greater impact on fps as poor modeling. That's why it's important to keep the collision as simple as possible and therefore I created yet another, even simpler version of the car tire that will be invisible in the game and is only used to block the player. Most people do not realize how simple and blocky the environments in games really are. The visuals may be highly detailed and realistic but the movement is limited by flat walls and big cubes.

Putting all this together, the lod models, the collision model and several textures we end up with one simple game asset that can be placed in any map:

Did you like this post? Would you like to see more of these entries focusing on level design? Let me know what you think.

And as always, have a happy day! :)
comments: Feel free to discuss this on our forums

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