Texture Mapping from Watt, Ch' 8

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Texture Mapping from Watt, Ch. 8

• Jonathan Han

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Topics Discussed

• Texture Map to Models
• Bump Maps, Light Maps
• Environment (Reflection) Mapping
• 3D Textures
• Interactive Texture Mapping

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What is Mapping?

• Assigning colors to the
• pixels on a 3D model to
• simulate. . .
• Color
• Specular color
• Surface perturbation
• Transparency

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2D Texture Maps to Polygon Mesh Objects

• Association of 2 coordinate systems between the
  mesh and the map
• Inverse Mapping vs. Forward Mapping
• Bilinear Interpolation
• Problem is parametrization of object surface

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Mapping by Intermediate Surface

• Map -gt (S map) Simple 3D shape -gt (O map)
  Projection onto complex mesh
• Plane, cylinder, cube, spheres all possible
  intermediate shapes

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O Mapping
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O Mapping Result
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Bi-Cubic Parametric Patch

• If an object is already a quadric or a cubic,
  then the surface possess a coordinate system that
  covers every point already.
• Simply multiply u and v by the resolution in
  pixels to obtain location on texture map

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Parametric Example
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Parametric Patch (contd)

• Divide mesh up to individual parametric surfaces,
  and place the texture over each

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Parametric Patch (contd)

• Assign (u, v) coordinates to points on mesh
  surface, and interpolate between these points

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Billboards

• Technique to create pseudo-realistic 3D objects
  when viewed in constricted directions

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Bump mapping

• Simulation for surface perturbation without
  adding polygons to the mesh
• The lighting changes per-pixel to achieve said
  simulation

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What is a Bump Map?

• Array of values that represent objects height
  variation on small scale
• Combined with surface normal to evaluate lighting
  equation

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Light Maps

• Like Bump Maps, Light Maps store information on a
  surface thats not just color
• Simulate localized lighting
• Same map applied to multiple mesh to create the
  same lighting pattern

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Light Maps Example
No light maps
With light maps
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Environmental Mapping

• To substitute expensive ray-tracing for modelling
  shiny objects, 2D environment map are textured
  onto the object.

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Creating an Environmental Map

• Sphere map
• Render scene from opposite angle of output
  camera, and apply as texture map
• Problem Inaccurate when the object is round

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Creating an Environmental Map

• Ball Map
• Create a mirrored sphere and place at approximate
  location of object render the sphere.
• Problem Non-uniform sampling at non-original
  viewpoint

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Creating an Environmental Map

• Cube Map
• Place a camera at location of object and remove
  object take snapshots at 6 directions.

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Extended Environmental Mapping

• Surface Properties
• 2 maps diffuse and specular, combined like in
  Phong shading
• Diffuse Indexed by surface normal
• Specular Indexed by reflected view vector

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3-D Texture Domains

• Instead of a 2D texture pattern, why not make the
  texture 3D?
• Circumvent problems in texture compression and
  texture continuity
• Problem Only have texture that are defined in 3D

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Easy Example

• If Z-axis integer is even, make it red. If not,
  make it white.

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Easy Example No. 2

• Sine and ramp functions

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3D Noise

• Used to distort existing texture to form
  irregular and interesting patterns

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Perlins Noise Lattice

• The Perlins Method of Noise Generation
• Lattice of points (i,j,k), where i, j, and k are
  integers each assigned a random number. Values
  between i, j, and k linearly (or otherwise)
  interpolated

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Adjusting Noise

• Instead of noise(x,y,z), we can use
  noise(fx,fy,fz) a to fine-tune result
• f frequency
• a - amplitude

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Creating Recognizable Textures

• Turbulate stripes to emulate marble texture
• (marble(x) marble_colour (sin(x turbulence(x))

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3D Textures for Animation

• Emulate flame by adding time dimension to 3D
  Texture Map
• Successive slices of noise rendered for
  flickering flame

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Interactive Texturing

• Assist artists in creating helpful textures
• Applet
• Applet

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Interactivity in Texturing Symmetrical Models

• Model placed in bounding box
• Artist paints profile texture as 2D image
• Image plane-textured onto the model
• Artist adjusts image and re-render for results

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Painting Textures

• Artist paints textures onto models directly
• Imbues shading, glossiness, as well as pattern to
  model spontaneously as artist selects it

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Implementing Texture Paint

• Auxiliary frame buffer item buffer created
• Screen cursors location on model gives pointer
  to position on object surface
• Requires parametrized surface divide objects
  surface into numerous micropolygons

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Discussion

• Additional possibilities for clever ways around
  expensive modelling?
• Applications for 3D textures and noise? In
  combination with environmental mapping? In
  combination with light maps and bump maps?