display_element(3G)

NAME

display_element − display current element on the specified graphics display device

SYNOPSIS

C Syntax:

void display_element(fildes, devdes)
int fildes, devdes;

FORTRAN77 Syntax:

subroutine display_element(fildes, devdes)
integer*4 fildes, devdes

Pascal Syntax:

procedure display_element(fildes, devdes:integer);

DESCRIPTION

Input Parameters

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

devdes Integer file descriptor returned by gopen when an I/O path to a graphics output device is opened. This file descriptor identifies the graphics display device on which the current elment will be displayed.

Discussion

Display_element displays the current element from the open segment of the specified graphics display device.

Display_element generates errors if:

• fildes does not identify a display list device;

• the current element of the open segment is element 0 (element 0 cannot be displayed);

• there is no currently open segment in the display list identified by fildes.

If the current element is a call_segment or execute_segment element, the segment network is traversed, beginning with the referenced segment. If the current element is a cond_call_segment or cond_execute_segment element, the segment referenced by that element is traversed if the conditions specified with that element are met.

If a segment is open on graphics display device devdes, the current element is also copied to the open segment on devdes. If the current element is a call_segment or execute_segment element, it is expanded, flattening the segment network as it is copied. If the current element is a cond_call_segment or cond_execute_segment element, it is expanded if the conditions specified by its parameters are satisfied. Elements in a segment that follow a cond_return element are copied only if the conditions of the cond_return are not satisfied. The cond_return element is never copied to the open segment. The implicit push_state and pop_state of execute_segment and cond_execute_segment will be copied to the open segment as explicit push_state and pop_state elements.

Set_traversal_depth(3G) can be used to limit the traversal depth. The default maximum traversal depth limits traversal processing to 42 segment-referencing elements; these are call_segment, execute_segment, cond_call_segment and cond_execute_segment). If traversal of one of these elements would exceed the maximum traversal depth, a warning is generated and the element is not traversed.

Segment network traversal can also be limited by display traversal control elements (see set_pick_traversal_control(3G)), segment control (see seg_control(3G)), individual element control (see ele_control(3G)), and the invisibility and highlighting filters (see set_invisibility_filter(3G) and set_highlighting_filter(3G)).

Output from the display traversal process is subject to buffering (see buffer_mode(3G)). If buffering is enabled, output from the display traversal process will not be displayed until the buffer is flushed. Calling make_picture_current(3G) will make sure that this has been done.

When display_element(3G) is called using the HP 98736, the VDMA interface will be used automatically.

ERRORS

1 Graphics device is not initialized for this operation.

24 Segment not open.

36 At element 0 - element 0 cannot be displayed.

40 Fildes not a display list device.

1042 Warning: Traversal attempted beyond specified maximum traversal depth.

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