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Deciding what resolution (height and width) and file format to use for the texture in your project is important. A variety of factors can influence your decisions.
The first thing to realize is that texture resolutions must be in what is known as a Power of Two. The more common texture resolutions are as follows:
Game consoles have a very limited amount of texture memory compared to computers; therefore, smaller resolutions are generally used. For example, a single character model created for a particular Playstation2 game required the use of three textures— two 256 × 256 textures for the body and one 64 × 64 texture for the head. On the other hand, characters created for a PC game I was involved with used one or possibly two 512 × 512 textures each. Your Art Director and programming team will tell you what kind of texture limitations your project will have.
When creating your textures, you should create the texture larger than you actually need for your project. This will allow you to pack more detail into the image, and it will give you the ability to use a variety of different texture resolutions from the larger source file when creating a game for multiple platforms with different resolution requirements. I generally recommend creating a texture one Power of Two larger than the maximum file resolution. If your game will use a 512 × 512 texture, create the texture at 1024 × 1024 and shrink the image upon completion.
For our Silenus project, we will use one 512 × 512 for the body, one 256 × 256 for the head, and one 256 × 256 for the sword. When creating the textures, we will use one Power of Two larger (one 1024 × 1024 and two 512 × 512).
Many image formats are available in the UV Snapshot options; however, you
probably will want to use either Targa (.tga) or TIFF (.tif) formats because they keep
alpha channel information and they are frequently used in modern game engines. For
our project, we will use .tga. Either format will work just fine.
Your standard game texture is an RGB image (using Red, Green, and Blue channels). Adding a fourth channel creates what is called an alpha channel. This extra channel holds secondary texture information in the form of a grayscale image that can be used in a variety of ways depending on the game engine. Alpha channels are most commonly used for the following:
Opacity/Transparency This is probably the most common use of an alpha channel. In the alpha, wherever the alpha is white, the model will be opaque; wherever the alpha is black, the model will be transparent.
Specularity This is another very common use of an alpha channel in games. Wherever the alpha is white, the model will be highly specular or shiny; wherever the alpha is black, the model will have no specularity.
Incandescence Not quite as common is the use of an alpha channel for incandescence, which will create a glow effect where the alpha is white.
Reflectivity Similar to Specularity, except instead of a simple white specular highlight where the alpha is white, the model will reflect a created reflectivity texture map. The reflectivity map is usually a Cube Map, which is a type of texture that is used by the game engine to project an image from all around the model. This type of map is used mostly for reflectivity as you project sky from above, trees and buildings from the sides, and grass or dirt from the floor. These are created in a variety of ways, and your project director should be able to let you know how your particular job handles it.
Other alpha channel effects are commonly used in the case of pixel shaders, which are becoming much more prevalent in modern games. Pixel shaders have special render effects on a per-pixel basis on the model, as opposed to the more common pervertex method that had been used previously. Arguably, the most dramatic pixel shader effect is the use of bump maps and normal maps.
Bump Maps and Normal Maps Bump maps and normal maps are very similar in purpose. They convey irregular surface information where geometry is not available or would not be plausible to do so (for example, the surface texture of a piece of clothing or the scaly skin of a creature). The main differences between the two kinds of maps are the method of creating them and the quality of their results.
Bump maps are created by using a black-and-white image to convey height. White conveys higher; black conveys lower. On the contrary, a normal map is an RGB image that will calculate the vector of the light direction to convey depth much more realistically. Because it is not grayscale, a normal map is not used in the alpha channel of an image.
Displacement Maps Displacement Mapping is fairly new to the game industry. It actually uses the height information conveyed as a black-and-white image to push and pull the pixels of the texture file to adjust the texture perspective according to the camera view. This is pretty neat stuff—but for the purposes of our project, we will not use it. Your Art Director should be able to let you know if Displacement Mapping will be used in your project.
| Note: Depending on the game engine and how the graphics are handled, some alpha channel maps can be used as separate texture files instead.Because our Silenus project is being made with only Maya software and no game engine,we need to use most of these alpha channel effects as basic texture maps, rather than alpha channel effects, to see their results. |
Before we spend too much time on the different texture options that are available (we will get back to them soon) and while the concept of UVs is still fresh in your mind, let’s start UV Mapping Silenus. First, we will UV map his sword to get the hang of the process.
One thing to keep in mind when planning your textures is what kind of game you are developing. Obviously, you can expect this 3500-polygon character to be rather prominently featured in the game. The sword may also be very visible. With this information, you can more accurately plan what resolution textures you will want to use. I am going to plan for a texture map that is 256 × 256 for the sword. For development, we will go one Power of Two larger and create the texture at a resolution of 512 × 512.
Character_
Final.mb from Tutorials/Chapter2/Project_Character/Scenes on the CD.
Select the character, and hide it from view (Ctrl+H).| Note: To make working with your model’s UVs a little easier, you can use one of Maya’s pre-saved panel layouts. In your chosen view panel’s menus, navigate to Panels > Saved Layouts > Persp/UV Texture Editor. If you would like to edit the layouts (as I did—I reversed the Persp/UV Texture Editor layout to be on opposite sides of the screen), you can change them with Panels > Saved Layouts > Edit Layouts…. |
2. With the UV Texture Editor displayed, select the sword’s blade. Use Edit Polygons > Texture > Planar Mapping UV projection with the mapping direction set to Z (if your model is oriented differently, you will need to change this to whichever direction you are using).
With the UVs projected, you can see the result in the UV Texture Editor. Projecting the UVs in this manner will map both sides of the blade from the same direction, effectively causing both sides of the sword to share UV space to maximize the texture usage.
Figure 3.7 Planar map the sword and position the UVs.
Figure 3.8 Auto map the sword’s square edge.
Figure 3.9 The blade UV mapped
Images/ mapping_grid_color.jpg. You can turn off Show Texture Image in
the UV Texture Editor so that you can better see the UVs above the image. (The
Hypershade is discussed later in this chapter, if you have trouble applying the
image to your model).
Figure 3.10 Cylindrical map the grip.
Figure 3.11 Position the grip UVs.
Figure 3.12 UV Mapping the hilt of the grip
Note: Select multiple objects in order to see multiple objects’ UV shells in the UV Texture Editor. |
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Created: March 27, 2003
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