3D graphics eBook - Course Materials Repository

Texel 211
change the location from a three-element vector to a two-element vector with values ranging from zero to one (uv). [3]
These values are multiplied by the resolution of the texture to obtain the location of the texel. When a texel is
requested that is not on an integer position, texture filtering is applied.
Clamping & Wrapping
When a texel is requested that is outside of the texture, one of two techniques is used: clamping or wrapping.
Clamping limits the texel to the texture size, moving it to the nearest edge if it is more than the texture size.
Wrapping moves the texel in increments of the texture's size to bring it back into the texture. Wrapping causes a
texture to be repeated; clamping causes it to be in one spot only.
References
[1] Andrew Glassner, An Introduction to Ray Tracing, San Francisco: Morgan–Kaufmann, 1989
[2] Linda G. Shapiro and George C. Stockman, Computer Vision, Upper Saddle River: Prentice–Hall, 2001
[3] Tomas Akenine-Moller, Eric Haines, and Naty Hoffman, Real-Time Rendering, Wellesley: A K Peters, 2008
Texture atlas
In realtime computer graphics, a texture atlas is a large image, or "atlas" which contains many smaller sub-images,
each of which is a texture for some part of a 3D object. The sub-textures can be rendered by modifying the texture
coordinates of the object's uvmap on the atlas, essentially telling it which part of the image its texture is in. In an
application where many small textures are used frequently, it is often more efficient to store the textures in a texture
atlas which is treated as a unit by the graphics hardware. In particular, because there are less rendering state changes
by binding once, it can be faster to bind one large texture once than to bind many smaller textures as they are drawn.
For example, a tile-based game would benefit greatly in performance from a texture atlas.
Atlases can consist of uniformly-sized sub-textures, or they can consist of textures of varying sizes (usually restricted
to powers of two). In the latter case, the program must usually arrange the textures in an efficient manner before
sending the textures to hardware. Manual arrangement of texture atlases is possible, and sometimes preferable, but
can be tedious. If using mipmaps, care must be taken to arrange the textures in such a manner as to avoid sub-images
being "polluted" by their neighbours.
External links
• Texture Atlas Whitepaper [1] - A whitepaper by NVIDIA which explains the technique.
• Texture Atlas Tools [2] - Tools to create texture atlases semi-manually.
• Practical Texture Atlases [3] - A guide on using a texture atlas (and the pros and cons).
References
[1] http:/ / download. nvidia. com/ developer/ NVTextureSuite/ Atlas_Tools/ Texture_Atlas_Whitepaper. pdf
[2] http:/ / developer. nvidia. com/ content/ texture-atlas-tools
[3] http:/ / www. gamasutra. com/ features/ 20060126/ ivanov_01. shtml