Controlling How Textures are Mapped

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
	0.0 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):

Texturing a face

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

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

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

Classic VRML Encoding

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

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

Classic VRML Encoding

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

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

Classic VRML Encoding

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

Syntax: Appearance

An Appearance node describes overall shape appearance:

• textureTransform - transform

XML Encoding

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

Classic VRML Encoding

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

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

Classic VRML Encoding

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

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

Classic VRML Encoding

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