Texture Mapping

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Texture Mapping
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Why texture?

• Detail is expensive to model
• Often the surface of an object is viewed only
  from a distance
• We can paint the detail on the object instead
  of increasing the complexity of the object

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How is it done?

• As we draw each pixel of a surface, we get the
  local colour from the texture image.
• So we need a coordinate system on the surface to
  find the right bit of the texture.

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Just use x, y?
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u, v Mapping
v
u
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Remember shading and normals?

• Each vertex carries shading and/or normal vector
  values for interpolation.
• Give each vertex u, v values too.
• The interpolation can be done by software or
  hardware.

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Scan-line interpolation
a
b
p
u's
us
Scan line y s
us ub(uc-ub)(s - by)/(cy by) similarly u's
and up, vp
c
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Ways to get u, v
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Parametric surfaces
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Different uses of texture
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Ray traced?
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Bump mapping
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Bump Mapping Examples
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Problems

• Undersampling one pixel maps to an area covering
  many texture pixels (texels)
• Oversampling many pixels map to an area
  contained by only one texel.

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Undersampling
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Under-sampling
COSC326 Lecture 17
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Oversampling
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Oversampling
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Surface and volume texture
2D
3D
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Functional Textures
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Movie Example