SFSGFA(3NCARG)

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

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