| 233 |
|
n dx dy dz set surface normal for current vertex |
| 234 |
|
_ _ _ |
| 235 |
|
f v1 v2 v3 ... polygon using current material, spec. vertices |
| 236 |
+ |
fh v1 v2 v3 - ... face with explicit holes |
| 237 |
|
sph vc radius sphere |
| 238 |
|
cyl v1 radius v2 truncated right cylinder (open-ended) |
| 239 |
|
cone v1 rad1 v2 rad2 truncated right cone (open-ended) |
| 2070 |
|
Also, specified normals should point in the general direction of the |
| 2071 |
|
surface for best results. |
| 2072 |
|
.LP |
| 2073 |
< |
There is no explicit representation of holes in MGF. A hole must be |
| 2074 |
< |
represented implicitly by connecting vertices to form "seams." For |
| 2073 |
> |
There is no explicit representation of holes in this entity, but see |
| 2074 |
> |
the |
| 2075 |
> |
.UL fh |
| 2076 |
> |
entity for an alternative specification. |
| 2077 |
> |
.LP |
| 2078 |
> |
A hole may be represented implicitly in a face entity |
| 2079 |
> |
by connecting vertices to form "seams." |
| 2080 |
> |
For |
| 2081 |
|
example, a wall with a window in it might look as shown in Figure 1. |
| 2082 |
|
In many systems, the wall itself would be represented with the first |
| 2083 |
|
list of vertices, (v1,v2,v3,v4) and the hole associated with that |
| 2084 |
< |
wall as a second set of vertices (v5,v6,v7,v8). In MGF, we must |
| 2084 |
> |
wall as a second set of vertices (v5,v6,v7,v8). |
| 2085 |
> |
Using the face entity, we must |
| 2086 |
|
give the whole thing as a single polygon, connecting the vertices so |
| 2087 |
|
as to create a "seam," as shown in Figure 2. |
| 2088 |
< |
This could be written in MGF as "f v1 v2 v3 v4 v5 v6 v7 v8 v5 v4". |
| 2088 |
> |
This could be written as "f v1 v2 v3 v4 v5 v6 v7 v8 v5 v4". |
| 2089 |
|
.LP |
| 2090 |
|
It is very important that the order of the hole be opposite to the |
| 2091 |
|
order of the outer perimeter, otherwise the polygon will be |
| 2134 |
|
.LP |
| 2135 |
|
.UL cone, |
| 2136 |
|
.UL cyl, |
| 2137 |
+ |
.UL fh, |
| 2138 |
+ |
.UL m, |
| 2139 |
+ |
.UL prism, |
| 2140 |
+ |
.UL ring, |
| 2141 |
+ |
.UL sph, |
| 2142 |
+ |
.UL torus, |
| 2143 |
+ |
.UL v |
| 2144 |
+ |
.ds RH FH |
| 2145 |
+ |
.bp |
| 2146 |
+ |
.SH |
| 2147 |
+ |
NAME |
| 2148 |
+ |
.LP |
| 2149 |
+ |
fh - create a polygonal face with explicit holes |
| 2150 |
+ |
.SH |
| 2151 |
+ |
SYNOPSIS |
| 2152 |
+ |
.LP |
| 2153 |
+ |
.B fh |
| 2154 |
+ |
.I "p1 p2 ... - h1.1 h1.2 ... - h2.1 h2.2 ..." |
| 2155 |
+ |
.SH |
| 2156 |
+ |
DESCRIPTION |
| 2157 |
+ |
.LP |
| 2158 |
+ |
Create a polygonal face with optional holes made of the current material. |
| 2159 |
+ |
The first contour is the outer perimeter, with vertices given in |
| 2160 |
+ |
counter-clockwise order as seen from the front side (the same as the |
| 2161 |
+ |
.UL f |
| 2162 |
+ |
entity). |
| 2163 |
+ |
A hole is indicated by a hyphen ('-') followed by the hole's |
| 2164 |
+ |
vertices, given in clockwise order as seen from the front side. |
| 2165 |
+ |
Multiple hole contours are separated by additional hyphens. |
| 2166 |
+ |
There must be at least three vertices for each contour, and the |
| 2167 |
+ |
last vertex is implicitly connected to the first. |
| 2168 |
+ |
If any vertex is undefined, an error will result. |
| 2169 |
+ |
.LP |
| 2170 |
+ |
If any vertices have associated surface normals, they will be used |
| 2171 |
+ |
instead of the average plane normal, though it is safest to specify |
| 2172 |
+ |
either all normals or no normals, and to stick with triangles |
| 2173 |
+ |
when normals are used. |
| 2174 |
+ |
Also, specified normals should point in the general direction of the |
| 2175 |
+ |
surface for best results. |
| 2176 |
+ |
.SH |
| 2177 |
+ |
EXAMPLE |
| 2178 |
+ |
.DS |
| 2179 |
+ |
# Make a wall with a window using an explicit hole. |
| 2180 |
+ |
# (See Figures 1 and 2.) |
| 2181 |
+ |
fh v1 v2 v3 v4 - v5 v6 v7 v8 |
| 2182 |
+ |
.DE |
| 2183 |
+ |
.SH |
| 2184 |
+ |
SEE ALSO |
| 2185 |
+ |
.LP |
| 2186 |
+ |
.UL cone, |
| 2187 |
+ |
.UL cyl, |
| 2188 |
+ |
.UL f, |
| 2189 |
|
.UL m, |
| 2190 |
|
.UL prism, |
| 2191 |
|
.UL ring, |
