SFSGFA fills the area defined by the points (XRA(I),YRA(I)), for I from 1 to NRA. The lines connecting
point 1 to point 2, point 2 to point 3, . . ., point NRA-1 to point NRA, and point NRA to point 1 bound
the area to be filled.
The values of the internal parameter 'TY' (for 'TYPE OF FILL') and the argument ICI determine how the
fill is done. The function of ICI changes depending on the value of 'TY'. ICI can determine the fill
area color index, the polyline color index, or the density of the fill pattern.
'TY' = 0 This is the default. SFSGFA does color fill by calling GFA. GFA does either hollow, solid,
or pattern fill. Hollow fill (only boundaries are drawn) is GFA's default, but you can change
the type of fill by calling the GKS subroutine GSFAIS. Notice that one of the first steps in
the code for the example "sfex02" is to force solid fill by calling GSFAIS with the argument
"1".
A value of ICI greater than or equal to zero specifies the color index of the fill area.
A value of ICI less than zero specifies that the fill area color index is not to be set
before calling GFA; the last call to the GKS subroutine GSFACI then determines the fill area
color index.
'TY' = 1 SFSGFA fills the area with parallel lines by calling SFWRLD.
A value of ICI greater than or equal to zero specifies the polyline color index.
A value of ICI less than zero specifies that the polyline color index is not to be set before
calling SFWRLD; the last call to the GKS subroutine GSPLCI determines the polyline color
index.
Parameters 'AN', 'CH', 'DO', and 'SP' further affect the nature of the fill.
Note: If 'CH' and 'DO' are set to select dot fill or character fill, the values of ICI will
not affect the color of the dots or characters. The intended use of 'TY' > 0 is to do color
fill using colored lines; no provision is made for the use of colored dots or colored
characters. (The current values of the polymarker and text color indices are used to
determine the color.)
'TY' = 2 SFSGFA calls SFWRLD to fill the area with parallel lines and calls SFNORM to fill the area
again with parallel lines perpendicular to the first set.
ICI, if zero or greater, specifies the polyline color index.
A negative value of ICI specifies that the polyline color index is not to be set before
calling SFWRLD; the last call to the GKS subroutine GSPLCI determines the polyline color
index.
Parameters 'AN', 'CH', 'DO', and 'SP' further affect the nature of the fill. See the note
above about ICI's function with 'CH' and 'DO'.
'TY' = -4, -3, -2, -1
SFSGFA fills the area with line patterns by calling SFWRLD and/or SFNORM. The absolute value
of 'TY' determines the maximum number of fill-line angles used in a pattern.
ICI determines the density of the lines drawn at each angle.
Angles Used: When 'TY' has one of the following values, fill is done by using lines drawn at
the angles shown ('AN' is an internal parameter that specifies an angle in degrees):
'TY' Angles Used (in Degrees)
-1 'AN'
-2 'AN', 'AN'+90
-3 'AN', 'AN'+60, 'AN'+120
-4 'AN', 'AN'+45, 'AN'+90, 'AN'+135
Line Density: ICI is used to select the density of the lines in each direction. A zero or
negative value of ICI selects a blank pattern. Positive values of ICI select patterns that
increase in density as the value of ICI increases. The largest usable value of ICI is
approximately 5*ABS('TY'); beyond that, the pattern becomes essentially solid. For example,
if 'TY' is -4, 20 is about the largest value of ICI that you can use and still see a pattern.
For each increase in ICI, fill lines are added at one of the usable angles. The first time
lines are added at a given angle, they are spaced 32*'SP' units apart. (The default value of
the internal parameter 'SP' is .00125.) After the first time, each time lines are added at a
given angle, they are added between the existing lines so that the distance between lines at
that angle is halved. An ICI value that is evenly divisible by the absolute value of 'TY'
yields a pattern that is evenly dense at all angles. For example, if 'TY' has the value -2,
the patterns associated with the first three values of ICI are formed as follows: ICI=1 uses
lines at the angle 'AN', spaced 32*'SP' units apart; ICI=2 uses lines at the angles 'AN' and
'AN'+90, both spaced 32*'SP' units apart; ICI=3 uses lines at the angle 'AN', spaced 32*'SP'
units apart, and lines at the angle 'AN'+90, spaced 16*'SP' units apart.
For SFSGFA to fill an uncomplicated polygon (one without holes), XRA and YRA should contain the world
coordinates of the polygon's vertices in the order in which they are encountered as the boundary of the
polygon is traced.
To leave an unfilled hole in a polygon, do the following: (1) add the vertices of the hole, in the proper
order, to XRA and YRA; (2) repeat the first vertex of the hole to close it; (3) repeat the last vertex of
the outer polygon boundary to tie the first point of the hole to the last point of the polygon's outer
boundary.
To fill what was unfilled and vice versa, do the following: (1) add the four coordinates of the frame
corners; (2) repeat the coordinates of the first corner of the frame; (3) repeat the final point of the
original polygon. In effect, this makes what was previously inside, outside, and what was previously
outside, inside.
When a polygon contains holes, there are connecting lines between the outer boundary of the polygon and
the boundaries of the holes. When doing software fill (internal parameter 'TY' not equal to 0), these
connecting lines cause no trouble; however, when doing solid fill (internal parameter 'TY'= 0), the
hardware fill algorithms will frequently display unfortunate edge effects along such lines. You can
minimize these effects by using only horizontal or vertical connecting lines and by ensuring they do not
cross any of the original boundary lines.
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