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.\" SCCSid "$SunId$ LBL" |
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.\" RCSid "$Id$" |
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.nr PS 11 |
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.ps 11 |
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.nr VS 12 |
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n dx dy dz set surface normal for current vertex |
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_ _ _ |
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f v1 v2 v3 ... polygon using current material, spec. vertices |
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fh v1 v2 v3 - ... face with explicit holes |
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sph vc radius sphere |
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cyl v1 radius v2 truncated right cylinder (open-ended) |
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cone v1 rad1 v2 rad2 truncated right cone (open-ended) |
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= = = = = |
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Object o - - - |
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Transform xf - - T{ |
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f, sph, cyl, cone, |
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f, fh, sph, cyl, cone, |
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ring, torus, prism |
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T} |
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Material m 2-sided black T{ |
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sides, rd, td, |
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ed, rs, ts, ir |
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T} T{ |
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f, sph, cyl, cone, |
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f, fh, sph, cyl, cone, |
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ring, torus, prism |
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T} |
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Color c neutral grey T{ |
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(0,0,0), |
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no normal |
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T} p, n T{ |
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< |
f, sph, cyl, cone, |
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f, fh, sph, cyl, cone, |
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ring, torus, prism |
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T} |
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.TE |
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.TS |
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lw(.75i) lw(1.75i) lw(3i). |
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f v1 v2 v3 ... polygon using current material, spec. vertices |
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fh v1 v2 v3 - ... face with explicit holes |
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sph vc radius sphere |
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cyl v1 radius v2 truncated right cylinder (open-ended) |
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cone v1 rad1 v2 rad2 truncated right cone (open-ended) |
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require a normal direction. |
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An |
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.UL f |
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or |
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.UL fh |
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entity will interpolate vertex normals if given, and |
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use the polygon plane normal otherwise. |
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See the |
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.UL cone, |
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.UL cyl, |
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.UL f, |
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.UL fh, |
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.UL n, |
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.UL p, |
1950 |
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.UL prism, |
1989 |
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.UL cone, |
1990 |
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.UL cyl, |
1991 |
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.UL f, |
1992 |
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.UL fh, |
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.UL n, |
1994 |
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.UL prism, |
1995 |
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.UL ring, |
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SEE ALSO |
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.LP |
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.UL f, |
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.UL fh, |
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.UL p, |
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.UL prism, |
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.UL ring, |
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Also, specified normals should point in the general direction of the |
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surface for best results. |
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.LP |
2079 |
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There is no explicit representation of holes in MGF. A hole must be |
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represented implicitly by connecting vertices to form "seams." For |
2079 |
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There is no explicit representation of holes in this entity, but see |
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the |
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.UL fh |
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entity for an alternative specification. |
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.LP |
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A hole may be represented implicitly in a face entity |
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by connecting vertices to form "seams." |
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For |
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example, a wall with a window in it might look as shown in Figure 1. |
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In many systems, the wall itself would be represented with the first |
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list of vertices, (v1,v2,v3,v4) and the hole associated with that |
2090 |
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wall as a second set of vertices (v5,v6,v7,v8). In MGF, we must |
2090 |
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wall as a second set of vertices (v5,v6,v7,v8). |
2091 |
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Using the face entity, we must |
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give the whole thing as a single polygon, connecting the vertices so |
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as to create a "seam," as shown in Figure 2. |
2094 |
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This could be written in MGF as "f v1 v2 v3 v4 v5 v6 v7 v8 v5 v4". |
2094 |
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This could be written as "f v1 v2 v3 v4 v5 v6 v7 v8 v5 v4". |
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.LP |
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It is very important that the order of the hole be opposite to the |
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order of the outer perimeter, otherwise the polygon will be |
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.LP |
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.UL cone, |
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.UL cyl, |
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.UL fh, |
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.UL m, |
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.UL prism, |
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.UL ring, |
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.UL sph, |
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.UL torus, |
2149 |
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.UL v |
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.ds RH FH |
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.bp |
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.SH |
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NAME |
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.LP |
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fh - create a polygonal face with explicit holes |
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.SH |
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SYNOPSIS |
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.LP |
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.B fh |
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.I "p1 p2 ... - h1.1 h1.2 ... - h2.1 h2.2 ..." |
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.SH |
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DESCRIPTION |
2163 |
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.LP |
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Create a polygonal face with optional holes made of the current material. |
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The first contour is the outer perimeter, with vertices given in |
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counter-clockwise order as seen from the front side (the same as the |
2167 |
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.UL f |
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entity). |
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A hole is indicated by a hyphen ('-') followed by the hole's |
2170 |
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vertices, given in clockwise order as seen from the front side. |
2171 |
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Multiple hole contours are separated by additional hyphens. |
2172 |
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There must be at least three vertices for each contour, and the |
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last vertex is implicitly connected to the first. |
2174 |
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If any vertex is undefined, an error will result. |
2175 |
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.LP |
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If any vertices have associated surface normals, they will be used |
2177 |
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instead of the average plane normal, though it is safest to specify |
2178 |
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either all normals or no normals, and to stick with triangles |
2179 |
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when normals are used. |
2180 |
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Also, specified normals should point in the general direction of the |
2181 |
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surface for best results. |
2182 |
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.LP |
2183 |
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Vertices should not be shared between any two contours. |
2184 |
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I.e., a hole should not share a vertex or edge with the perimeter or |
2185 |
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another hole, or incorrect rendering may result. |
2186 |
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.SH |
2187 |
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EXAMPLE |
2188 |
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.DS |
2189 |
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# Make a wall with a window using an explicit hole. |
2190 |
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# (See Figures 1 and 2.) |
2191 |
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fh v1 v2 v3 v4 - v5 v6 v7 v8 |
2192 |
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.DE |
2193 |
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.SH |
2194 |
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SEE ALSO |
2195 |
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.LP |
2196 |
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.UL cone, |
2197 |
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.UL cyl, |
2198 |
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.UL f, |
2199 |
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.UL m, |
2200 |
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.UL prism, |
2201 |
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.UL ring, |
2202 |
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.UL sph, |
2203 |
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.UL torus, |
2204 |
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.UL v |
2205 |
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.ds RH SPH |
2206 |
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.bp |
2207 |
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.SH |
2250 |
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.UL cone, |
2251 |
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.UL cyl, |
2252 |
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.UL f, |
2253 |
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.UL fh, |
2254 |
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.UL m, |
2255 |
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.UL prism, |
2256 |
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.UL ring, |
2308 |
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.LP |
2309 |
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.UL cone, |
2310 |
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.UL f, |
2311 |
+ |
.UL fh, |
2312 |
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.UL m, |
2313 |
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.UL prism, |
2314 |
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.UL ring, |
2381 |
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.LP |
2382 |
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.UL cyl, |
2383 |
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.UL f, |
2384 |
+ |
.UL fh, |
2385 |
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.UL m, |
2386 |
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.UL prism, |
2387 |
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.UL ring, |
2448 |
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.UL cyl, |
2449 |
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.UL cone, |
2450 |
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.UL f, |
2451 |
+ |
.UL fh, |
2452 |
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.UL m, |
2453 |
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.UL ring, |
2454 |
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.UL sph, |
2505 |
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.UL cyl, |
2506 |
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.UL cone, |
2507 |
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.UL f, |
2508 |
+ |
.UL fh, |
2509 |
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.UL m, |
2510 |
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.UL prism, |
2511 |
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.UL sph, |
2566 |
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.UL cyl, |
2567 |
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.UL cone, |
2568 |
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.UL f, |
2569 |
+ |
.UL fh, |
2570 |
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.UL m, |
2571 |
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.UL prism, |
2572 |
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.UL ring, |
3927 |
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|
3928 |
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typedef struct { |
3929 |
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int clock; /* incremented each change -- resettable */ |
3930 |
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char *client_data; /* pointer to private client data */ |
3931 |
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FVECT p, n; /* point and normal */ |
3932 |
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} C_VERTEX; /* vertex context */ |
3933 |
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.DE |
3949 |
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(See the |
3950 |
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.I xf_handler |
3951 |
|
page.)\0 |
3952 |
+ |
The |
3953 |
+ |
.I client_data |
3954 |
+ |
pointer may be used to index private application data for vertex |
3955 |
+ |
linking, etc. |
3956 |
+ |
This pointer is initialized to NULL when the context is created, |
3957 |
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and otherwise ignored by the parser library. |
3958 |
|
.LP |
3959 |
< |
It is possible but not recommended to alter the contents of the |
3959 |
> |
It is possible but not recommended to alter the shared contents of the |
3960 |
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vertex structure returned by |
3961 |
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.I c_getvert. |
3962 |
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Normally it is read during the |
4077 |
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|
4078 |
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typedef struct { |
4079 |
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int clock; /* incremented each change */ |
4080 |
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char *client_data; /* pointer to private client data */ |
4081 |
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short flags; /* what's been set */ |
4082 |
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short ssamp[C_CNSS]; /* spectral samples, min wl to max */ |
4083 |
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long ssum; /* straight sum of spectral values */ |
4093 |
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This is a convenient way to keep track of whether or not a color has |
4094 |
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changed since its last use. |
4095 |
|
The |
4096 |
+ |
.I client_data |
4097 |
+ |
pointer may be used to index private application data. |
4098 |
+ |
This pointer is initialized to NULL when the context is created, |
4099 |
+ |
and otherwise ignored by the parser library. |
4100 |
+ |
The |
4101 |
|
.I flags |
4102 |
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member indicates which color representations have been assigned, |
4103 |
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and is an inclusive OR of one or more of the following: |
4242 |
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|
4243 |
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typedef struct { |
4244 |
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int clock; /* incremented each change -- resettable */ |
4245 |
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char *client_data; /* pointer to private client data */ |
4246 |
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int sided; /* 1 if surface is 1-sided, 0 for 2-sided */ |
4247 |
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float nr, ni; /* index of refraction, real and imaginary */ |
4248 |
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float rd; /* diffuse reflectance */ |
4266 |
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desired. |
4267 |
|
This is a convenient way to keep track of whether or not a material has |
4268 |
|
changed since its last use. |
4269 |
+ |
The |
4270 |
+ |
.I client_data |
4271 |
+ |
pointer may be used to index private application data. |
4272 |
+ |
This pointer is initialized to NULL when the context is created, |
4273 |
+ |
and otherwise ignored by the parser library. |
4274 |
|
.LP |
4275 |
|
All reflectance and transmittance values correspond to normal |
4276 |
|
incidence, and may vary as a function of angle depending on the |
4693 |
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The hardest part is translating the specular power to a roughness value. |
4694 |
|
For this, we recommend the following approximation: |
4695 |
|
.IP |
4696 |
< |
roughness = 0.6/sqrt(specular_power) |
4696 |
> |
roughness = sqrt(2/specular_power) |
4697 |
|
.LP |
4698 |
|
It is not a perfect correlation, but it is about as close as one can get. |
4699 |
|
.NH 3 |