Lecture20-TextureMapping

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

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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
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Texture Mapping Goal: add visual detail without adding geometric detail 8 polygons 8 polygons
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Typical Textures
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Replicating Textures
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Replicating Textures
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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
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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)
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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
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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:
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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 .
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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:
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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.
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Box Map This produces:
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Box Map Using a different set of textures:
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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...

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