BIT(3) Library Functions Manual BIT(3)
NAME
bit - screen graphics, mouse
SYNOPSIS
bind -a #b /dev
/dev/bitblt
/dev/mouse
/dev/mousectl
/dev/screen
#include <u.h>
#include <libg.h>
ushort BGSHORT(uchar *p)
ulong BGLONG(uchar *p)
void BPSHORT(uchar *p, ushort v)
void BPLONG(uchar *p, ulong v)
DESCRIPTION
The bit device provides the files bitblt, mouse, mousectl, and screen on machines with a bitmapped screen and a mouse. The device is
exclusive use.
The bit device provides, through the bitblt file, access to bitmaps, fonts, and subfonts in its private storage, as described in graph-
ics(2). Each object is identified by a short, its id. The bitmap with id zero is special: it represents the visible display. The subfont
with id zero is also special: it is initialized to a default subfont that is always available. There is no default font. There is also a
cursor associated with the screen; it is always displayed at the current mouse position. A process can write messages to bitblt to allo-
cate and free bitmaps, fonts, and subfonts, read or write portions of the bitmaps, and draw line segments, textures, and character strings
in the bitmaps. All graphics requests are clipped to their bitmaps. Some messages return a response to be recovered by reading bitblt.
The format of messages written to bitblt is a single lower case letter followed by binary parameters; multibyte integers are transmitted
with the low order byte first. The BPSHORT and BPLONG macros place correctly formatted two- and four-byte integers into a character buf-
fer. Some messages return a response formatted the same way; it usually starts with the upper case version of the request character.
BGSHORT and BGLONG retrieve values from a character buffer. Points are two four-byte numbers: x, y. Rectangles are four four-byte num-
bers: min x, min y, max x, and max y.
The following requests are accepted by the bitblt file. The numbers in brackets give the length in bytes of the parameters.
a ldepth[1] rect[16]
Allocate a bitmap. Ldepth is the log base 2 of the number of bits per pixel. Rect is a Rectangle giving the extent of the bitmap.
The bitmap is cleared to all zeros. The id of the allocated bitmap is returned on a subsequent read from bitblt, returning the three
bytes: followed by the id.
b dstid[2] dstpt[8] srcid[2] srcrect[16] code[2]
Bit-block transfer (bitblt) from a rectangle in the bitmap identified by srcid to a congruent rectangle at Point dstpt in the bitmap
identified by dstid. The rectangle is clipped against both source and destination bitmaps. See bitblt(2).
c [ pt[8] clr[32] set[32] ]
Switch mouse cursor. See the description of Cursors in graphics(2) for the meaning of the pt (the offset), set, and clr arguments.
If only is provided -- that is, if the message is one byte long -- the cursor changes to the default, typically an arrow.
e id[2] pt[8] value[1] code[2] n[2] pts[n*2]
Join the n+1 points pt and pts with n segments, exactly as for the l operator. The pts are specified by pairs of signed bytes holding
offsets from the previous point in the list.
f id[2]
Free the resources associated with the allocated bitmap identified by id.
g id[2]
Free the resources associated with the allocated subfont identified by id, including its bitmap. If the subfont is cached, the asso-
ciated data may be recoverable even after it has been freed; see below.
h id[2]
Free the resources associated with the allocated font identified by id.
i
Initialize the device. The next operation on bitblt should be a read(2). A read of length 34 returns information about the display:
I ldepth[1] rect[16] cliprect[16].
If the read count is large enough, the above information is followed by the header and character information of the default Subfont,
in the format expected by rdsubfontfile (see subfalloc(2) and font(6)). `Large enough' is 36 + 6n, where n is the number of charac-
ters in the subfont. The ids of the screen bitmap and default subfont are both zero.
j q0[4] q1[4]
Check to see whether a subfont with tags q0 and q1 is in the cache. If it is not, the write of the j message will draw an error. If
it is, the next read of bitblt will return
J id[2]
followed by the subfont information in the same format as returned by an init message; the subfont will then be available for use.
k n[2] height[1] ascent[1] bitmapid[2] q0[4] q1[4] info[6*(n+1)]
Allocate subfont. The parameters are as described in subfalloc(2), with info in external subfont file format. Bitmapid identifies a
previously allocated bitmap containing the character images. Q0 and q1 are used as labels for the subfont in the cache; if all ones,
the subfont will not be cached and hence shared with other applications. The id of the allocated subfont is recovered by reading from
bitblt the three bytes: followed by the id. Henceforth, the bitmap with id bitmapid is unavailable to the application; in effect, it
has been freed.
l id[2] pt1[8] pt2[8] value[1] code[2]
Draw a line segment from Point pt1 to Point pt2, using code for the drawing function, and value as the source pixel. See segment in
bitblt(2). Id identifies the destination bitmap.
m id[2]
Read the colormap associated with the bitmap with the specified id. The next read of bitblt will return 12*2^n bytes of colormap data
where n is the number of bits per pixel in the bitmap.
n height[1] ascent[1] ldepth[2] ncache[2]
Allocate a font with the given height, ascent, and ldepth. The id of the allocated font is recovered by reading from bitblt the three
bytes: followed by the id. The initial cache associated with the font will have ncache character entries of zero width.
p id[2] pt[8] value[1] code[2]
Change the pixel at Point pt using code for the drawing function, and value as the source pixel. See point in bitblt(2).
q id[2] rect[16]
Set the clipping rectangle for the bitmap with specified id to the given rectangle, which will itself be clipped to the bitmap's image
rectangle.
r id[2] miny[4] maxy[4]
Read rows ymin, ymin+1, ... ymax-1 of the bitmap with the given bitmap id. See the description of rdbitmap in balloc(2). A subse-
quent read of bitblt will return the requested rows of pixels. Note: in this case, the response does not begin with an to simplify
the reading of large bitmaps. Also, the reply may be too large to fit in a single 9P message (see read(5)), so multiple reads may be
necessary; each read will return only complete rows.
s id[2] pt[8] fontid[2] code[2] n[2] indices[2*n]
Draw using code code in the bitmap identified by id the text string specified by the n cache indices in font fontid, starting with the
upper left corner at pt.
t dstid[2] rect[16] srcid[2] code[2]
Texture the given rectangle in the bitmap identified by dstid by overlaying a tiling of the bitmap identified by srcid (aligning (0,0)
in the two bitmaps), and using code as a drawing code for bitblt; see texture in bitblt(2).
v id[2] ncache[2] width[2]
Reset, resize, and clear the cache for font id; the maximum width of the ncache characters the cache may hold is set to width. Must
be done before the first load of a cache slot. If the cache cannot be resized, the write of this message will fail but the cache will
be unaffected.
w id[2] miny[4] maxy[4] data[n]
Replace rows ymin, ymin+1, ... ymax-1 of the bitmap with the given bitmap id with the values in data. See the description of
wrbitmap in balloc(2).
x x[4] y[4]
Move the cursor so its origin is at (x,y).
y id[2] cacheindex[2] subfontid[2] subfontindex[2]
Load the description and image of character subfontindex in subfont subfontid into slot cacheindex of font id.
z id[2] map[m]
Replace the colormap associated with bitmap id with map, which contains m=12*2^n bytes of colormap data (see rgbpix(2) for the for-
mat).
A read of the mouse file returns the mouse status: its position and button state. The read blocks until the state has changed since the
last read. The read returns 14 bytes:
m buttons[1] x[4] y[4] msec[4]
where x and y are the mouse coordinates in the screen bitmap, msec is a time stamp, in units of milliseconds, and buttons has set the 1, 2,
and 4 bits when the mouse's left, middle, and right buttons, respectively, are down.
Writing to the mousectl file configures and controls the mouse. The messages are:
serial n sets serial port n to be the mouse port.
ps2 sets the PS2 port to be the mouse port.
accelerated turns on mouse acceleration.
linear turns off mouse acceleration
res n sets mouse resolution to a setting between 0 and 3 inclusive.
swap swaps the left and right buttons on the mouse.
Which messages are implemented is machine-dependent.
The screen file contains the screen bitmap in the format described in bitmap(6).
SOURCE
/sys/src/9/port/devbit.c
DIAGNOSTICS
Most messages to bitblt can return errors; these can be detected by a system call error on the write(see read(2)) of the data containing
the erroneous message. The most common error is a failure to allocate because of insufficient free resources. Most other errors occur
only when the protocol is mishandled by the application. Errstr(2) will report details.
BUGS
Because each message must fit in a single 9P message, subfonts are limited to about 1300 characters.
Can only change the color map of bitmap 0.
BIT(3)