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... 1.Color 2.Specular ‘color’ 3.Surface perturbation 4.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

O Mapping

O Mapping Result

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 Example

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 mapsWith 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

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

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

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?