Post

Controlling How Textures are Mapped

Posted Updated
By CREATE3000 4 min read

Motivation

  • By default, an entire texture image is mapped once around the shape
  • You can also:
    • Extract only pieces of interest
    • Create repeating patterns

Working through the texturing process

  • Imagine the texture image is a big piece of rubbery cookie dough
  • Select a texture image piece
    • Define the shape of a cookie cutter
    • Position and orient the cookie cutter
    • Stamp out a piece of texture dough
  • Stretch the rubbery texture cookie to fit a face

Using texture coordinate system

Texture images (the dough) are in a texture coordinate system:

  • S - direction is horizontal
  • T - direction is vertical
  • (0,0) at lower-left
  • (1,1) at upper-right

Specifying texture coordinates

Texture coordinates and texture coordinate indexes specify a texture piece shape (the cookie cutter):

 Coordinates
Texture Mapping 10.0 0.0 1.0 0.0 1.0 1.0 0.0 1.0

Applying texture transforms

Texture transforms translate, rotate, and scale the texture coordinates (placing the cookie cutter):

  
Texture Mapping 2Texture Mapping 3

Texturing a face

Bind the texture to a face (stretch the cookie and stick it):

  
Cookie 1Cookie 2

Working through the texturing process

  • Select piece with texture coordinates and indexes
    • Create a cookie cutter
  • Transform the texture coordinates
    • Position and orient the cookie cutter
  • Bind the texture to a face
    • Stamp out the texture and stick it on a face
  • The process is very similar to creating faces!

Syntax: TextureCoordinate

A TextureCoordinate node contains a list of texture coordinates:

XML Encoding

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<TextureCoordinate
    point='0.2 0.2, 0.8 0.2, ...'/>

Classic Encoding

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TextureCoordinate {
  point [ 0.2 0.2, 0.8 0.2, ... ]
}

Used as the texCoord field value of IndexedFaceSet or ElevationGrid nodes.

Syntax: IndexedFaceSet

An IndexedFaceSet geometry node creates geometry out of faces:

  • texCoord and texCoordIndex - specify texture pieces

XML Encoding

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<Shape>
  <Appearance><!-- ... --></Appearance>
  <IndexedFaceSet
      texCoordIndex='...'
      coordIndex='...'>
    <TextureCoordinate ... />
    <Coordinate ... />
  </IndexedFaceSet>
</Shape>

Classic Encoding

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Shape {
  appearance Appearance { ... }
  geometry IndexedFaceSet {
    texCoordIndex [ ... ]
    coordIndex [ ... ]
    texCoord TextureCoordinate { ... }
    coord Coordinate { ... }
  }
}

Syntax: ElevationGrid

An ElevationGrid geometry node creates terrains:

  • texCoord - specify texture pieces
  • Automatically generated texture coordinate indexes

XML Encoding

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<Shape>
  <Appearance><!-- ... --></Appearance>
  <ElevationGrid
      height='...'>
    <TextureCoordinate ... />
  </ElevationGrid>
</Shape>

Classic Encoding

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Shape {
  appearance Appearance { ... }
  geometry ElevationGrid {
    texCoord TextureCoordinate { ... }
    height [ ... ]
  }
}

Syntax: Appearance

An Appearance node describes overall shape appearance:

  • textureTransform - transform

XML Encoding

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<Shape>
  <Appearance>
    <Material ... />
    <ImageTexture ... />
    <TextureTransform ... />
  </Appearance>
  <!-- geometry ... -->
</Shape>

Classic Encoding

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Shape {
  appearance Appearance {
    material Material { ... }
    texture ImageTexture { ... }
    textureTransform TextureTransform { ... }
  }
  geometry ...
}

Syntax: TextureTransform

A TextureTransform node transforms texture coordinates:

  • translation - position
  • rotation - orientation
  • scale - size

XML Encoding

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<Shape>
  <Appearance>
    <Material ... />
    <ImageTexture ... />
    <TextureTransform
        translation='0.0 0.0'
        rotation='0.0'
        scale='1.0 1.0'/>
  </Appearance>
  <!-- geometry ... -->
</Shape>

Classic Encoding

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Shape {
  appearance Appearance {
    material Material { ... }
    texture ImageTexture { ... }
    textureTransform TextureTransform {
      translation 0.0 0.0
      rotation    0.0
      scale       1.0 1.0
    }
  }
  geometry ...
}

Scaling, rotating, and translating

Scale, Rotate, and Translate a texture cookie cutter one after the other:

XML Encoding

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<Shape>
  <Appearance>
    <Material ... />
    <ImageTexture ... />
    <TextureTransform
        translation='0.0 0.0'
        rotation='0.785'
        scale='8.5 8.5'/>
  </Appearance>
  <!-- geometry ... -->
</Shape>

Classic Encoding

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Shape {
  appearance Appearance {
    material Material { ... }
    texture ImageTexture { ... }
    textureTransform TextureTransform {
      translation 0.0 0.0
      rotation    0.785
      scale       8.5 8.5
    }
  }
  geometry ...
}

Read texture transform operations top-down:

  • The cookie cutter is translated, rotated, then scaled Order is fixed, independent of field order
  • This is the reverse of a Transform node

Summary

  • Texture images are in a texture coordinate system
  • Texture coordinates and indexes describe a texture cookie cutter
  • Texture transforms translate, rotate, and scale place the cookie cutter
  • Texture indexes bind the cut-out cookie texture to a face on a shape

Textures, Lights, and Environment

Tutorials
Controlling Textures Mapped
This post is licensed under CC BY 4.0 by the author.