cfb.4

<B>Digital的Unix操作系统VAX 4.2源码</B>

.TH cfb 4 RISC
.SH Name
cfb \- color bitmap graphics
.SH Syntax
.B "device 	cfb0	at ibus?	vector cfbvint"
.SH Description
.NXR "video subsystem" "cfb"
.NXR "cfb video subsystem" 
The video subsystem provides a half page or full page,
user-accessible bitmap display for graphics.
The subsystem consists of a 1 Mbyte (color)
block of dual port RAM, a mouse or tablet, a keyboard, and
a video monitor.
.PP
The subsystem device driver
supports a hybrid terminal with three minor devices.
The first minor device emulates a glass tty with a
screen that appears as an 80-column
by 56-row page that scrolls from the bottom.
This device is capable of being configured as the system console.
.PP
The second minor device is reserved for the mouse.
This device is a source of mouse state changes.
(A state change is defined as an X/Y axis
mouse movement or button change.)
When opened, the driver couples movements of the mouse with the cursor.
Mouse position changes are filtered and translated into cursor position
changes in an exponential manner.
Rapid movements result in large cursor position changes.
All cursor positions are range-checked to ensure that the cursor remains on
the display.
.PP
The third minor device provides an access path for console output
that does not disturb the graphics display.
The caller can open the device 
.PN /dev/xcons .
When this device is open, the graphics driver
redirects console device output to the input buffer of this device.
This mechanism disables
console output on the screen and saves the output for 
later display. This action preserves the graphic display integrity.
.PP
Input and output on the first and third minor devices are processed by
the standard line disciplines.
.PP
The Hold Screen key is supported. The graphics driver treats this
key as if CTRL/S or CTRL/Q has been entered. Pressing the Hold Screen key 
suspends the output (if it is not already suspended). To resume the output,
press the Hold Screen key again.
.SH Files
.TP 15
.PN /dev/console
Console terminal or graphics device
.TP
.PN /dev/mouse
Mouse or tablet graphics device
.TP
.PN /dev/xcons
Console message window for workstation
.SH See Also
console(4), devio(4), tty(4), ttys(5), MAKEDEV(8)