clear_control(3G)

NAME

clear_control − select type of clearing for subsequent clear_view_surface procedures

SYNOPSIS

C Syntax:

void clear_control(fildes,mode);
int fildes,mode;

FORTRAN77 Syntax:

subroutine clear_control(fildes,mode)
integer*4 fildes,mode

Pascal Syntax:

procedure clear_control(fildes,mode:integer);

DESCRIPTION

Input Parameters

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

mode The area to be cleared is specified with one of the following values:

CLEAR_VDC_EXTENT Clear virtual device coordinate extent area.

CLEAR_CLIP_RECTANGLE Clear clip rectangle area.

CLEAR_DISPLAY_SURFACE Clear entire display surface.

CLEAR_VIEWPORT Clear current viewport area.

In addition, the above values may be ORed with one or more of the following control flags:

CLEAR_ALL_BANKS For multibank devices, clear all graphics banks to zero simultaneously.

CLEAR_ZBUFFER Clear the zbuffer (if hidden surface removal is enabled) simultaneously with screen clears.

Discussion

For continuous-feed hardcopy devices, CLEAR_DISPLAY_SURFACE ejects the current page.

For multibank graphics devices, only the current bank as set by bank_switch is cleared. If CLEAR_ALL_BANKS is ORed with mode, all graphics banks are cleared to zero simultaneously, independent of write_enable, bank_switch, and background_color.

For devices supporting zbuffer hidden surface removal, the zbuffer will be cleared when clear_view_surface is called if CLEAR_ZBUFFER is ORed with mode. On devices which support zbuffer clearing at the same time as screen clearing, performance will be increased if the zbuffer is cleared in this manner, instead of using a separate call to zbuffer_switch. When CLEAR_ZBUFFER is enabled, zbuffer_switch will NOT clear the zbuffer.

DEFAULTS

Clear entire display surface. Do not clear all graphics banks; do not clear the zbuffer.

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