Texture mapping from watt ch 8
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Texture Mapping from Watt, Ch. 8 Jonathan Han Topics Discussed Texture Map to Models Bump Maps, Light Maps Environment (Reflection) Mapping 3D Textures Interactive Texture Mapping What is Mapping? Assigning colors to the pixels on a 3D model to simulate. . . Color Specular ‘color’

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Topics discussed l.jpg
Topics Discussed

  • Texture Map to Models

  • Bump Maps, Light Maps

  • Environment (Reflection) Mapping

  • 3D Textures

  • Interactive Texture Mapping


What is mapping l.jpg
What is Mapping?

Assigning colors to the

pixels on a 3D model to

simulate. . .

  • Color

  • Specular ‘color’

  • Surface perturbation

  • Transparency


2d texture maps to polygon mesh objects l.jpg
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 -> (S map) Simple 3D shape -> (O map) Projection onto complex mesh

  • Plane, cylinder, cube, spheres all possible intermediate shapes




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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 Patch (cont’d)

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


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Parametric Patch (cont’d)

  • 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 object’s 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 that’s 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


Easy example l.jpg
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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Perlin’s Noise Lattice

  • The Perlin’s 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


Adjusting noise l.jpg
Adjusting Noise

  • Instead of noise(x,y,z), we can use noise(f*x,f*y,f*z) * 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 cursor’s location on model gives pointer to position on object surface

  • Requires parametrized surface – divide object’s surface into numerous micropolygons


Discussion l.jpg
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?


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