NAME

       VVUDMV - This routine is the user-definable external subroutine used to draw masked vectors. The default
       version of the routine draws any polyline all of whose area identifiers are greater than or equal to
       zero.

SYNOPSIS

       CALL VVUDMV (XCS,YCS,NCS,IAI,IAG,NAI)

DESCRIPTION

       XCS         (REAL array, assumed size NCS, input): Array of X coordinates of the points defining the
                   polyline with the given set of area identifiers.

       YCS         (REAL array, assumed size NCS, input): Array of Y coordinates of the points defining the
                   polyline with the given set of area identifiers.

       NCS         (INTEGER, input): Number of points; assumed size of the X and Y coordinate arrays, XCS and
                   YCS.

       IAI         (INTEGER array, assumed size NAI, input): Array of area identifier values. Each value
                   represents the area identifier with respect to the area group in the area group array with
                   the same array index.

       IAG         (INTEGER array, assumed size NAI, input): Array of area-identifier groups.

       NAI         (INTEGER, input): Number of area identifier groups. The current version of Vectors supports
                   up to 64 area groups.

USAGE

       ´VVUDMV´ is the name given to the default version of the masked vector drawing routine, and it is also
       the name given to the argument through which the external subroutine is passed to VVECTR. However, you
       may choose any acceptable FORTRAN identifier as the name of a user-defined version of the routine. The
       substitute routine must have an argument list equivalent to the default version of VVUDMV. Also, whether
       or not the default version is used, the subroutine that calls VVECTR should contain an external
       declaration of the routine similar to the following:

               EXTERNAL VVUDMV

       If the MSK parameter is set to the value 1, specifying high precision masking, Vectors sends one set of X
       and Y polyline coordinate arrays to the area masking routine, ARDRLN, for each vector arrow. ARDRLN
       subdivides the polyline into pieces such that each smaller polyline has a single area identifier with
       respect to each area identifier group, then makes a call to VVUDMV for each polyline piece.  While the
       default version of VVUDMV only checks to see that none of the area identifiers are negative, a user-
       defined version could perform more complicated decision processing based on knowledge of the meaning of
       specific area identifier groups and/or area identifier values.  Note that, before invoking VVUDMV, ARDRLN
       modifies the user coordinate space by making the following calls:

               CALL GETSET(VPL,VPR,VPB,VPT,WDL,WDR,WDB,WDT,LLG) CALL SET(VPL,VPR,VPB,VPT,VPL,VPR,VPB,VPT,1)

       These calls temporarily turn the user to NDC mapping into an identity, allowing the user to call any of
       the routines, CURVE, CURVED, or the GKS routine GPL, to render the polygon piece , without worrying about
       a possible non-identity mapping between user and world coordinates.

       If MSK has a value greater than 1, specifying low precision masking, Vectors calls the routine ARGTAI to
       get the area identifiers with respect to the area identifier groups for a single point that locates the
       base position of the vector. Vectors then calls the VVUDMV routine itself, passing the coordinate arrays
       for a complete vector arrow.  Thus, a vector arrow whose base position is within an area to be masked can
       be eliminated, but an arrow whose base position is nearby, but outside, a masked area may intrude into
       the area. Also, in this case, since faster rendering is the goal, Vectors does not convert the coordinate
       arrays into normalized device coordinates and do the identity SET call. Therefore, the user should use
       only CURVE or CURVED to render the polyline, unless there is no possibility of a non-identity user to
       world coordinate mapping.

       The current version of Vectors supports masked drawing with up to 64 area groups. Vectors will exit with
       an error message if an area map with more than 64 groups is passed to it.

EXAMPLES

       Use the ncargex command to see the following relevant examples: ffex05, vvex01.

ACCESS

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

SEE ALSO

       Online: vectors, vectors_params, vvectr, vvgetc, vvgeti, vvgetr, vvinit, vvrset, vvsetc, vvseti, vvsetr,
       vvumxy, 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.