Texture Coordinates

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Texture coordinates, also called UVs, are pairs of numbers stored in the vertices of a mesh.

These numbers are often used to stretch a 2D texture onto a 3D mesh, but they can be used for other things like coloring the mesh (see Vertex color), controlling the flow across the surface (see Flow map), etc.

Game engines commonly use two texture coordinates, U and V, for mapping the width and height of a texture. A third axis W can also be used for depth if you are using a 3D volume texture, but usually this coordinate is removed for efficiency.

Texture coordinates are measured in a scale of 0.0 to 1.0, with 0.0 and 1.0 at opposite sides of the texture. When a model has a UV distance greater than 1 (for example, UV goes from -1 to 2) then the texture will tile across the model.

These numbers are usually hidden from the artist, replaced by helpful visual representations of how the textures are projected. Planes, cylinders and spheres help the artist align the textures in a visual way, but it helps to know that games only see the UV numbers that these shapes create.

UV Address Modes

Opengl clamping.png

Image by Open.GL.

There are four common methods for controlling how a texture is rendered when the UVs go beyond the 0-1 square. These methods can be chosen with a Shader.

  • Repeat or Wrap is usually the default. The texture will tile.
  • Mirror causes the texture to be flipped along each edge. Mirror has a tendency to create Rorschach/butterfly artifacts, but can be useful in certain situations like fences or railings.
  • Clamp causes the edge pixels to stretch outwards beyond the edges of the texture. Clamp is great for use with Cubemaps, since when the texture is filtered you don't want seams to appear along the edges of each cube face.
  • Border causes a solid color to appear outside the edge of the texture. Border is good for use with Decals, since you don't want the edges to tile and cause rendering seams.


UDIM is another address method, not used in games. UDIM allows multiple textures to be used by a single model, by offsetting the textures in whole units across UV space. UDIM is useful for texturing in television and film to increase the number of textures per model in a logical and uniform way.


Usually a single texture pattern is tiled by UV'ing the model outside the 0-1 square. However, multiple tiling textures can be arranged in a Texture atlas as sub-tiles and cropped out using a shader. The shader for this is more expensive than traditional texture tiling, but can be used if you are limited by the number of textures you can use.

UV Tutorials & Threads

Skankerzero uv mapping thoughts p1of4.png
Skankerzero uv mapping thoughts p2of4.png
Skankerzero uv mapping thoughts p3of4.png
Skankerzero uv mapping thoughts p4of4.png
UV mapping thought process. Images by Jesse "skankerzero" Sosa.
An automated UV projection network in Maya.
Image by Paul "prolow" Lohman.
How to edit multiple UV channels in 3ds Max.
Image by Carlos "cman2k" Montero.

UV Tools

Standalone

A standalone tool is one which is not directly integrated into another 3D package.

IPackThat by "[PB]Snoelk"

RoadKill by Francis O'Brien

UVLayout by Headus

3ds Max

Maya

Softimage / XSI

UV Map Grids

The grid is a texture to use while unwrapping a mesh. Sometimes called a custom UV map template, a UV checker, or a test grid.

Good things to have in a UV map grid:

  • A large checker grid to see large distortions.
  • A fine per-pixel grid to see small distortions.
  • Circles help with solving distortion, as it's easier for the human eye to see when a circle is distorted than a square.
  • Unique colors across the map, to see where the UV is tiling.
  • Letters and/or numbers to see when the UV is reversed.
  • Letters and/or numbers to see where a mesh feature is located in UV space.
Uvrefmap blackwhite.jpg
Uvrefmap blender.jpg
Uvrefmap checker green.gif
Uvrefmap checker util-mark.jpg
Uvrefmap checkeredmap.jpg
Uvrefmap circles.jpg
Uvrefmap circles letters.jpg
Uvrefmap circles noise.jpg
Uvrefmap circlesgreen noise.jpg
Uvrefmap circlessquares.jpg
Uvrefmap grid large.jpg
Uvrefmap grid small.jpg
Uvrefmap HarlequiN grid.jpg
Uvrefmap nvidia greengrid.jpg
Uvrefmap util-mark1.jpg
Uv mapping grid by cymae.jpg
Muse uv 01-01-1024x1024.jpg

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