Texture Mapping from Watt, Ch. 8

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# Texture Mapping from Watt, Ch. 8 - PowerPoint PPT Presentation

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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### 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’
• Surface perturbation
• Transparency
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
Mapping by Intermediate Surface
• Map -> (S map) Simple 3D shape -> (O map) Projection onto complex mesh
• Plane, cylinder, cube, spheres all possible intermediate shapes
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
Parametric Patch (cont’d)
• Divide mesh up to individual parametric surfaces, and place the texture over each
Parametric Patch (cont’d)
• Assign (u, v) coordinates to points on mesh surface, and interpolate between these points
Billboards
• Technique to create pseudo-realistic 3D objects when viewed in constricted directions
Bump mapping
• Simulation for surface perturbation without adding polygons to the mesh
• The lighting changes per-pixel to achieve said simulation
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
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
Light Maps Example

No light maps

With light maps

Environmental Mapping
• To substitute expensive ray-tracing for modelling shiny objects, 2D environment map are textured onto the object.
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
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
Creating an Environmental Map
• Cube Map:
• Place a camera at location of object and remove object – take snapshots at 6 directions.
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
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
• If Z-axis integer is even, make it red. If not, make it white.
Easy Example No. 2
• Sine and ramp functions
3D Noise
• Used to distort existing texture to form irregular and interesting patterns
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
• 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
Creating Recognizable Textures
• Turbulate stripes to emulate marble texture
• (marble(x) = marble_colour (sin(x + turbulence(x))
3D Textures for Animation
• Emulate flame by adding time dimension to 3D Texture Map
• Successive “slices” of noise rendered for flickering flame
Interactive Texturing
• Assist artists in creating helpful textures
• Applet
• Applet
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
“Painting” Textures
• Artist “paints” textures onto models directly
• Imbues shading, glossiness, as well as pattern to model spontaneously as artist selects it
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
• 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?