DISPLAY_ENABLE(3G)

NAME

display_enable − select which planes of a raster device are to be displayed

SYNOPSIS

C Syntax:

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

FORTRAN77 Syntax:

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

Pascal Syntax:

procedure display_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 to drive the visual output. Each bit is interpreted as the plane enable of that respective plane; i.e., If least significant bit is 0 then plane 1 is disabled. If 2nd bit is 1, then plane 2 is enabled, etc.

Discussion

Disabled frame buffer device planes drive the visual output as if they were zeros. For example, if the background_color_index is set to 170 (hex AA) and the display is cleared then: for plane_mask = 255 (hex FF), the color seen is the color at color table index 170. For plane_mask = 15 (hex 0F), the color seen is the color at color table index 10 (hex 0A), etc. This procedure, along with write_enable is very useful for writing into undisplayed bit planes while leaving the displayed planes unaltered (double-buffering).

For multi-bank graphics devices plane_mask is a byte quantity that affects the planes of all displayed banks simultaneously.

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). Use of display_enable and write_enable with double buffering is discouraged because of resulting interactions.

Some devices may not support this operation.

DEFAULTS

plane_index = 255:All planes (in first bank, if multi-bank) enabled.

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