Lecture20-TextureMapping

Lecture20-TextureMapping - Texture Mapping(Some Images from...

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Texture Mapping (Some Images from Rosalee Wolff)

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Texture Mapping Problem with shading models: -they assume that a diffuse surface has uniform reflectance This is okay for walls or pool balls, but not most objects We could add geometric complexity - BAD! Too time consuming Alternative: Texture mapping - Developed by Catmull (1974), Blinn and Newell (1976), and others
Texture Mapping Goal: add visual detail without adding geometric detail 8 polygons 8 polygons

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Typical Textures
Replicating Textures

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Replicating Textures
Textures Any image can be used as a texture map

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Texture Mapping There are both 2D and 3D versions of texture mapping 2D – “wallpaper” a 2D image onto an object 3D – “carve” a 3D object out of a block
2D Texture Mapping Given a 2D texture (image) and a 3D object, map the texture onto the object. Where does each point on the object map into the texture?

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Texture Map Shapes Planar Map Simply remove one of the object’s coordinates (project onto that coordinate plane)
Planar Map This has the unwanted side effect of keeping the texture constant in one direction. E.g., projecting along Z

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Planar Map Projecting along X and Y respectively
Cylindrical Map Instead of a planar map, we could use a cylindrical map ( x,y,z ) is converted to ( r, theta, height ). For texture mapping, theta is converted into a u - coordinate and height is converted into a v -coordinate. This wraps the two- dimensional texture map around the object.

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Cylindrical Map At minimum and maximum extents of the cylinder, the texture gets pinched together. E.g., a cylindrical map parallel to Z:
Cylindrical Map Similarly if the map is parallel to X or Y:

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Spherical Map Convert from (x, y, z) to spherical coordinates. Latitude is converted to a u-coordinate , longitude is converted to a v-coordinate .
Spherical Map This still has the effect of pinching the texture at the poles, but differently than using a cylindrical map.

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Spherical Map With the poles in the X and Y directions:
Box Map We can use a collection of planar maps to provide better coverage than using a single planar map:

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Box Map We project each plane onto its portion of the object. Use the object’s normal to determine which texture to use.
Box Map This produces:

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Box Map Using a different set of textures:
Box Map We get:

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Map Entity To texture map, we take an (x, y, z) value from the object and determine a (u, v) texture value. How we determine what we use as the (x, y, z) value is
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Lecture20-TextureMapping - Texture Mapping(Some Images from...

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