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.
SEE ALSO¶
Online: softfill, softfill_params, sfgetc, sfgeti, sfgetp, sfgetr, sfsetc,
sfseti, sfsetp, sfsetr, sfwrld, ncarg_cbind
Hardcopy: NCAR Graphics Fundamentals, UNIX Version
COPYRIGHT¶
Copyright (C) 1987-2009
University Corporation for Atmospheric Research
The use of this Software is governed by a License Agreement.