| OCR Text |
Show 1 2.3.1 Description of Texture Maps A texture map is an array of surface attributes. These surface attribute includ such things as color values, shading parameters, surface normal perturbations, or as proposed by this thesis, displacement values for surface perturbations. Data structures for texture maps are detailed in the next section. Consider the texture map as a two-dimensional array. The fundamental process of texture mapping is to define a transformation that will map the world coordinate {x, y, z) into a map coordinate (u,v). Once such a transformation is defined it can be used to rnap the texture onto the object during rendering. 2.3.2 Mapping Texture onto Objects The mapping of texture onto objects requires a transformation that takes threedimensional space onto a two-dimensional map. In the case of a polygon this involves a projection onto the texture map. A straight projection would not maintain perspective since texture appears smaller as it gets farther away. It is also necessary to perform the transformation in a consistent manner so that the texture is consistent across borders of objects. The usual method is to compute a transformation matrix that maps the texture map onto the polygon. The inverse of this matrix can then be multiplied by any coordinate on the polygon to produce map coordinates. The transformation calculation also requires three parameters for each index ( usize, urepeat, utrans) and (vsize, vrepeat, vtrans). The usize and vsize pa- |
