dl_label(3G)

NAME

dl_label − insert a display list label into the currently open segment

SYNOPSIS

C Syntax:

void dl_label(fildes, label_id)
int fildes, label_id;

FORTRAN77 Syntax:

subroutine dl_label(fildes, label_id)
integer*4 fildes, label_id

Pascal Syntax:

procedure dl_label(fildes, label_id:integer);

DESCRIPTION

Input Parameters

fildes Integer file descriptor returned by gopen when an I/O path to a graphics device is opened.

label_id Label identifier used for element pointer positioning and returned by picking. Must be a non-zero value.

Discussion

Dl_label inserts a dl_label element containing the specified label identifier label_id into the currently open segment of the specified graphics device following the current element. The display list label can then be used for element pointer positioning and can be returned as the result of a pick.

While it is possible to define more than one display list label with the same label identifier within a segment, the practice is discouraged because it introduces ambiguity into both element pointer positioning and picking operations. It also degrades the performance of set_ele_ptr_relative_to_label. If two or more labels in a given segment have the same identifier, set_ele_ptr_relative_to_label positions the element pointer relative to the first display list label encountered following the current element. If no display list label with the specified identifier is found between the current element and the end of the segment, the search for a label continues, beginning with the first element in the segment.

If label_id is zero, an error is generated because label identifier 0 is reserved. A pick path contains a label equal to zero when the element identified in the pick path precedes any display list labels in the segment. When set_ele_ptr_relative_to_label is called with label_id set to zero, element pointer positioning is relative to element zero. Thus, information returned from pick operations can always be used to edit the picked segment, positioning the element pointer at the picked element.

ERRORS

1 Graphics device is not initialized for this operation.

6 Invalid parameter value - label identifier is 0.

24 Segment not open.

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