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.