Ubuntu Manpage: SFSGFA - (which stands for "SOFTFILL - Simulate GFA") fills, in one of various ways, an

NAME

       SFSGFA - (which stands for "SOFTFILL - Simulate GFA") fills, in one of various ways, an
       area of the plotter frame defined by a given set of points; it is intended to provide a
       way to use the GKS fill-area routine, if it works (as is the case in the version of GKS
       distributed with NCAR Graphics), or a suitable pattern-fill substitute, otherwise.  Doing
       all area fills with SFSGFA has the advantage that the way in which they are done can then
       be changed by modifying the value of a single internal parameter of Softfill, named 'TY'.

SYNOPSIS

       CALL SFSGFA (XRA, YRA, NRA, DST, NST, IND, NND, ICI)

C-BINDING SYNOPSIS

       #include <ncarg/ncargC.h>

       void c_sfsgfa (float *xra, float *yra, int nra,
       float *dst, int nst, int *ind, int nnd, int ici)

DESCRIPTION

XRA (an input/output array of type REAL, dimensioned NRA or greater) contains the
X coordinates of the points defining the area to be filled, in the user
coordinate system. Upon return, the contents of XRA will have been converted
to the fractional coordinate system.

YRA (an input/output array of type REAL, dimensioned NRA or greater) contains the
Y coordinates of the points defining the area to be filled, in the user
coordinate system. Upon return, the contents of YRA will have been converted
to the fractional coordinate system.

NRA (an input expression of type INTEGER) is the number of points defining the
area to be filled. NRA must be greater than two.

DST (a scratch array of type REAL, dimensioned NST) is for use when fill lines are
generated by means of calls to SFWRLD and/or SFNORM.

NST (an input expression of type INTEGER) is the length of the array DST. NST must
be greater than or equal to NRA + NIM, where NIM is the largest number of
intersection points of any fill line with the boundary lines. To be sure DST
is large enough, use NIM = NRA; in practice, NIM rarely needs to be that
large. For a convex polygon, for example, NIM = 2.

IND (a scratch array of type INTEGER, dimensioned NND) is for use when fill lines
are generated by means of calls to SFWRLD and/or SFNORM.

NND (an input expression of type INTEGER) is the length of the array IND. It must
be greater than or equal to NRA + 2 * NIM, where NIM is as defined above.

ICI (an input expression of type INTEGER) is, nominally, the fill-area color index
to be used. When the internal parameter 'TY' has a value other than zero, ICI
may be used in some other manner.

C-BINDING DESCRIPTION

       The C-binding argument descriptions are the same as the Fortran argument descriptions.

USAGE

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.

EXAMPLES

       Use the ncargex command to see the following relevant examples: cpex04, cpex05, sfex02,
       tsoftf fsfsgfa.

ACCESS

       To use SFSGFA or c_sfsgfa, load the NCAR Graphics libraries ncarg, ncarg_gks, and ncarg_c,
       preferably in that order.

MESSAGES

       See the softfill man page for a description of all Softfill error messages and/or
       informational messages.

COPYRIGHT

       Copyright (C) 1987-2009
       University Corporation for Atmospheric Research

       The use of this Software is governed by a License Agreement.