WRITE_ENABLE(3G)

NAME

write_enable − select modifiable planes of frame buffer device

SYNOPSIS

C Syntax:

void write_enable(fildes,plane_mask);
int fildes;
int plane_mask;

FORTRAN77 Syntax:

subroutine write_enable(fildes,plane_mask)
integer*4 fildes,plane_mask

Pascal Syntax:

procedure write_enable(fildes,plane_mask:integer);

DESCRIPTION

Input Parameters

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

plane_mask
Mask used to determine which planes are enabled for modification. Each bit is interpreted as the plane enable of that respective plane; i.e., if the least significant bit is 0 then plane 1 is disabled. If the 2nd bit is 1, then plane 2 is enabled, etc.

Discussion

If a plane is disabled, writing into the frame buffer will not affect that plane. For example, if the plane_mask is 15 (hex 0F) and 170 (hex AA) is written into a location containing 85 (hex 55), that location will change to 90 (hex 5A).

All raster operations and output primitives are affected by write_enable.

For multi-bank graphics devices plane_mask is a byte quantity that affects the corresponding planes of all banks simultaneously. See bank_switch to enable a bank of eight planes for writing. Graphics devices that support video blending may treat the plane mask as a 24 bit quantity while blending is enabled.

Write_enable is not supported on certain devices.

Double-buffering with 12 planes or with fewer than 6 planes uses display_enable and write_enable to select buffers (other values use bank_switch). During double buffering, display_enable and write_enable are applied to only the displayed and written planes as determined by double_buffering.

DEFAULTS

plane_mask = 255:All planes are enabled.

Museum

Related Articles