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<H1><A ID="SECTION00910000000000000000"> Texturing Functions</A> </H1> <DL> <DT><#4982#><#4982#></DT> <DD><#1477#><TT>blotch</TT><#1477#> <#1478#>BlendFactor surface<#1478#> Produces a mildly interesting blotchy-looking surface. <#673#>BlendFactor<#673#> is used to control the interpolation between the default surface characteristics and the characteristics of the given surface. A value of 0 results in a roughly 50-50 mix of the two surfaces. Higher values result in a great portion of the default surface characteristics. </DD> </DL> <DL> <DT><#4983#><#4983#></DT> <DD><#1481#><TT>bump</TT><#1481#> <#1482#>scale<#1482#> Apply a random bump map. The point of intersection is passed to <#678#>DNoise()<#678#>. The returned normalized vector is weighted by <#679#>scale<#679#> and the result is added to the normal vector at the point of intersection. </DD> </DL>Using an image texture applied to the ``bump'' component offers a more direct way to control the modification of surface normals (see below). <DL> <DT><#4984#><#4984#></DT> <DD><#1485#><TT>checker</TT><#1485#> ;SPMlt;<#1486#>Surface<#1486#>;SPMgt; Applies a 3D checkerboard texture. Every point that falls within an ``even'' unit cube will be assigned the characteristics of the named surface applied to it, while points that fall within ``odd'' cubes will have its usual surface characteristics. Be wary of strange effects due to roundoff error that occur when a planar checkered surface lies in a plane of constant integral value (e.g., z = 0) in texture space. In such cases, simply translate the texture to ensure that the planar surface is not coincident with an integral plane in texture space (e.g., <#684#><TT>translate 0 0 0.1</TT><#684#>). </DD> </DL> <DL> <DT><#4988#><#4988#></DT> <DD><#1489#><TT>cloud</TT><#1489#> <#1490#>scale H λ octaves cthresh lthresh tscale<#1490#> This texture is a variant on Geoff Gardner's ellipsoid-texturing algorithm. It should be applied to unit spheres centered at the origin. These spheres may, of course, be transformed at will to form the appropriately-shaped cloud or tree. A sample of normalized <#689#>fBm<#689#> (see the <#690#>fbm<#690#> texture) is generated at the point of intersection. This sample is used to modulate the surface transparency. The final transparency if a function of the sample value, the the proximity of the point of intersection to the edge of the sphere (as seen from the ray origin), and three parameters to control the overall ``density.'' The proximity of the point to the sphere edge is determined by evaluating a <#691#>limb<#691#> function, which varies from 0 on the limb to 1 at the center of the sphere. <tex2html_verbatim_mark>#math149#<DIV ALIGN="CENTER"> transp = 1. - <tex2html_image_mark>#tex2html_wrap_indisplay4991#⇧ </DIV> </DD> </DL> <DL> <DT><#4992#><#4992#></DT> <DD><#1493#><TT>fbm</TT><#1493#> <#1494#>offset scale H λ octaves thresh<#1494#> [<#1495#>colormap<#1495#>] Generate a sample of discretized fractional Brownian motion (fBm) and uses it to scale the diffuse and ambient component of an object's surface. <#699#>Scale<#699#> is used to scale the value returned by the fBm function. <#700#>Offset<#700#> allows one to control the minimum value of the fBm function. <#701#>H<#701#> is the <#702#>Holder exponent<#702#> used in the fBm function (a value of 0.5 works well). λ is used to control <#703#>lacunarity<#703#>, and specifies the the frequency difference between successive samples of the fBm basis function (a value of 2.0 will suffice). <#704#>Octaves<#704#> specifies the number of octaves (samples) to take of the fBm basis function (in this case, Noise()). Between five and seven octaves usually works well. <#705#>Thresh<#705#> is used to specify a lower bound onthe output of the fBm function. Any value lower than <#706#>thresh<#706#> is set to zero. If a <#707#>colormap<#707#> is named, a 256-entry colormap is read from the named file, and the sample of fBm is scaled by 255 and is used as an index into the colormap. The resulting colormap entry is used to scale the ambient and diffuse components of the object's surface. </DD> </DL> <DL> <DT><#4995#><#4995#></DT> <DD><#1498#><TT>fbmbump</TT><#1498#> <#1499#>offset scale H λ octaves<#1499#> Similar to the <#712#>fbm<#712#> texture. Rather than modifying the color of a surface, this texture acts as a bump map. </DD> </DL> <DL> <DT><#4997#><#4997#></DT> <DD><#1502#><TT>gloss</TT><#1502#> <#1503#>glossiness<#1503#> Gives reflective surfaces a glossy appearance. This texture perturbs the object's surface normal such that the normal ``samples'' a cone of unit height with radius <tex2html_verbatim_mark>#math150#1. - glossiness. A value of 1 results in perfect mirror-like reflections, while a value of 0 results in extremely fuzzy reflections. For best results, jittered sampling should be used to render scenes that make use of this texture. </DD> </DL> <DL> <DT><#4999#><#4999#></DT> <DD><#1506#><TT>marble</TT><#1506#> [<#1507#>colormap<#1507#>] Gives a surface a marble-like appearance. The texture is implemented as roughly parallel alternating veins of marble, each of which is separated by 1/7 of a unit and runs perpendicular to the Z axis. If a colormap is named, the surface's ambient and diffuse colors will be scaled using the RGB values in the colormap. If no colormap is given, the diffuse and ambient components are simply scaled by the value of the marble function. One may transform the texture to control the density and orientation of the marble veins. </DD> </DL> <DL> <DT><#5000#><#5000#></DT> <DD><#1510#><TT>sky</TT><#1510#> <#1511#>scale H λ octaves cthresh ltresh<#1511#> Similar to the <#725#>fbm<#725#> texture. Rather than modifying the color of a surface, this texture modulates its transparency. <#726#>cthresh<#726#> is the value of the <#727#>fBm<#727#> function above which the surface is totally opaque. Below <#728#>lthresh<#728#>, the surface is totally transparent. </DD> </DL> <DL> <DT><#5002#><#5002#></DT> <DD><#1514#><TT>stripe</TT><#1514#> ;SPMlt;<#1515#>Surface<#1515#>;SPMgt; <#1516#>size bump<#1516#> ;SPMlt;Mapping;SPMgt; Apply a ``raised'' stripe pattern to the surface. The surface properties used to color the stripe are those of the given surface. The width of the stripe, as compared to the unit interval, is given by <#734#>size<#734#>. The magnitude of <#735#>bump<#735#> controls the extent to which the bump appears to be displaced from the rest of the surface. If negative, the stripe will appear to sink into the surface; if positive, it will appear to stand out of the surface. </DD> </DL>Mapping functions are described below. <DL> <DT><#5007#><#5007#></DT> <DD><#1519#><TT>wood</TT><#1519#> Gives a surface a wood-like appearance. The feature size of this texture is approximately 0.01 of a unit, making it often necessary to scale the texture in order to achieve the desired appearance. </DD> </DL>