The GBLKVP subroutine is a graphical call that defines a blanking viewport.

The arguments to the GBLKVP subroutine are as follows:

viewport

is a numeric matrix or literal that defines a viewport. This rectangular area’s boundary is specified in normalized coordinates, where you specify the coordinates of the lower left corner and the upper right corner of the rectangular area in the form

{minimum-x minimum-y maximum-x maximum-y}

inside

is a numeric argument that specifies whether the graphics output is to be clipped inside or outside the blanking area. The default is to clip outside the blanking area.

The GBLKVP subroutine defines an area, called the blanking area, in which nothing is drawn until the area is released. This routine is useful for clipping areas outside the graph or for blanking out inner portions of the graph. If inside is set to 0 (the default), no graphics output appears outside the blanking area. Setting inside to 1 clips inside the blanking areas.

The blanking area (as specified by the viewport argument) is defined on the current viewport, and it is released when the viewport is changed or popped. At most one blanking area is in effect at any time. The blanking area can also be released by the GBLKVPD subroutine or another GBLKVP call. The coordinates in use for this graphics command are given in normalized coordinates because they are defined relative to the current viewport.

For example, to blank out a rectangular area with corners at the coordinates (20,20) and (80,80) relative to the currently defined viewport, use the following statement:

call gblkvp({20 20 80 80});

No graphics or text can be written outside this area until the blanking viewport is ended.

Alternatively, if you want to clip inside the rectangular area, use the inside parameter, as follows:

call gblkvp({20 20 80 80}, 1);

See also the description of the CLIP option in the RESET statement.