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

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.

UNIX                                               March 1993                                     SFSGFA(3NCARG)