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 as set by vdc_extent.

CLEAR_CLIP_RECTANGLE Clear clip area as set by clip_rectangle.

CLEAR_DISPLAY_SURFACE Clear entire display surface.

CLEAR_VIEWPORT Clear current viewport area as set by view_port.

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

CLEAR_ALL_BANKS For multi-bank devices, clear all graphics banks to zero simultaneously.

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

Discussion

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

For multi-bank 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 Z-buffer hidden surface removal, the Z-buffer will be cleared when clear_view_surface is called if CLEAR_ZBUFFER is ORed with mode. On devices which support Z-buffer clearing at the same time as screen clearing, performance will be increased if the Z-buffer 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 Z-buffer.

DEFAULTS

Clear entire display surface. Do not clear all graphics banks; do not clear the Z-buffer.

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