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The draw device serves a three–level file system providing an interface
to the graphics facilities of the system. Each client of the device
connects by opening /dev/draw/new and reading 12 strings, each
11 characters wide followed by a blank: the connection number
(n), the image id (q.v.) of the display image
(always zero), the channel format of the image, the replicate
bit, the min.x, min.y, max.x, and max.y of the display image,
and the min.x, min.y, max.x, and max.y of the clipping rectangle.
The channel format string is described in image(6), and the other
fields are decimal numbers.
The client can then open the directory /dev/draw/n/ to access
the ctl, data, colormap, and refresh files associated with the
connection.
Via the ctl and data files, the draw device provides access to
images and font caches in its private storage, as described in
graphics(2). Each image is identified by a 4–byte integer, its
id.
Reading the ctl file yields 12 strings formatted as in /dev/draw/new,
but for the current image rather than the display image. The current
image may be set by writing a binary image id to the ctl file.
A process can write messages to data to allocate and free images,
fonts, and subfonts; read or write portions of the images; and
draw line segments and character strings in the images. All graphics
requests are clipped to their images. Some messages return a response
to be recovered by reading the data file.
The format of messages written to data is a single 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
buffer. BGSHORT and BGLONG retrieve values from a
character buffer. Points are two four–byte numbers: x, y. Rectangles
are four four–byte numbers: min x, min y, max x, and max y. Images,
screens, and fonts have 32–bit identifiers. In the discussion of
the protocol below, the distinction between identifier and actual
image, screen, or font is not made, so that ``the
object id'' should be interpreted as ``the object with identifier
id''. The definitions of constants used in the description below
can be found in draw.h.
The following requests are accepted by the data file. The numbers
in brackets give the length in bytes of the parameters.
A id[4] imageid[4] fillid[4] public[1]
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Allocate a new Screen (see window(2)) with screen identifier id
using backing store image imageid, filling it initially with data
from image fillid. If the public byte is non–zero, the screen can
be accessed from other processes using the publicscreen interface.
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b id[4] screenid[4] refresh[1] chan[4] repl[1] r[4*4] clipr[4*4]
color[4]
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Allocate an image with a given id on the screen named by screenid.
The image will have rectangle r and clipping rectangle clipr.
If repl is non–zero, the image's replicate bit will be set (see
draw(2)).
Refresh specifies the method to be used to draw the window when
it is uncovered. Refbackup causes the server to maintain a backing
store, Refnone does not refresh the image, and Refmesg causes
a message to be sent via the refresh file (q.v.).
The image format is described by chan, a binary version of the
channel format string. Specifically, the image format is the catenation
of up to four 8–bit numbers, each describing a particular image
channel. Each of these 8–bit numbers contains a channel type in
its high nibble and a bit count in its low nibble.
The channel type is one of CRed, CGreen, CBlue, CGrey, CAlpha,
CMap, and CIgnore. See image(6).
Color is the catenation of four 8–bit numbers specifying the red,
green, blue, and alpha channels of the color that the new image
should be initially filled with. The red channel is in the highest
8 bits, and the alpha in the lowest. Note that color is always
in this format, independent of the image format.
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c dstid[4] repl[1] clipr[4*4]
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Change the replicate bit and clipping rectangle of the image dstid.
This overrides whatever settings were specified in the allocate
message.
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d dstid[4] srcid[4] maskid[4] dstr[4*4] srcp[2*4] maskp[2*4]
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Use the draw operator to combine the rectangle dstr of image dstid
with a rectangle of image srcid, using a rectangle of image maskid
as an alpha mask to further control blending. The three rectangles
are congruent and aligned such that the upper left corner dstr
in image dstid corresponds to the point srcp
in image srcid and the point maskp in image maskid. See draw(2).
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D debugon[1]
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If debugon is non–zero, enable debugging output. If zero, disable
it. The meaning of ``debugging output'' is implementation dependent.
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e dstid[4] srcid[4] c[2*4] a[4] b[4] thick[4] sp[2*4] alpha[4]
phi[4]
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Draw an ellipse in image dst centered on the point c with horizontal
and vertical semiaxes a and b. The ellipse is drawn using the
image src, with the point sp in src aligned with c in dst. The
ellipse is drawn with thickness 1+2xthick.
If the high bit of alpha is set, only the arc of the ellipse from
degree angles alpha to phi is drawn. For the purposes of drawing
the arc, alpha is treated as a signed 31–bit number by ignoring
its high bit.
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E dstid[4] srcid[4] center[2*4] a[4] b[4] thick[4] sp[2*4] alpha[4]
phi[4]
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Draws an ellipse or arc as the e message, but rather than outlining
it, fills the corresponding sector using the image srcid. The
thick field is ignored, but must be non–negative.
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f id[4]
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Free the resources associated with the image id.
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F id[4]
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Free the screen with the specified id. Windows on the screen must
be freed separately.
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i id[4] n[4] ascent[1]
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Treat the image id as a font cache of n character cells, each
with ascent ascent.
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l cacheid[4] srcid[4] index[2] r[4*4] sp[2*4] left[1] width[1]
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Load a character into the font cache associated with image cacheid
at cache position index. The character data is drawn in rectangle
r of the font cache image and is fetched from the congruent rectangle
in image srcid with upper left corner sp. Width specifies the
width of the character--the spacing from this
character to the next--while left specifies the horizontal distance
from the left side of the character to the left side of the cache
image. The dimensions of the image of the character are defined
by r.
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L dstid[4] p0[2*4] p1[2*4] end0[4] end1[4] thick[4] srcid[4] sp[2*4]
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Draw a line of thickness 1+2xthick in image dstid from point p0
to p1. The line is drawn using the image srcid, translated so
that point sp in srcid aligns with p0 in dstid. The end0 and end1
fields specify whether the corresponding line end should be a
square, a disc, or an arrow head. See line in draw(2) for
more details.
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N id[4] in[1] j[1] name[j]
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If in is non–zero, associate the image id with the string name.
If in is zero and name already corresponds to the image id, the
association is deleted.
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n id[4] j[1] name[j]
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Introduce the identifier id to correspond to the image named by
the string name.
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o id[4] r.min[2*4] scr[2*4]
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Position the window (layer) id so that its upper left corner is
at the point scr on its screen. Simultaneously change its internal
(logical) coordinate system so that the point r.min corresponds
to the upper left corner of the window, see memlorigin(2).
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O op[1]
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Set the compositing operator to op for the next draw operation.
(The default is SoverD).
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p dstid[4] n[2] end0[4] end1[4] thick[4] srcid[4] sp[2*4] dp[2*2*(n+1)]
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Draw a polygon of thickness 1+2xthick. It is conceptually equivalent
to a series of n line–drawing messages (see L above) joining adjacent
points in the list of points dp. The source image srcid is translated
so that the point sp in srcid aligns with the first point in the
list dp. The polygon need not be closed:
end0 and end1 specify the line endings for the first and last
point on the polygon. All interior lines have rounded ends to
make smooth joins.
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P dstid[4] n[2] wind[4] ignore[2*4] srcid[4] sp[2*4] dp[2*2*(n+1)]
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Draw a polygon as the p message, but fill it rather than outlining
it. The winding rule parameter wind resolves ambiguities about
what to fill if the polygon is self–intersecting. If wind is ~0,
a pixel is inside the polygon if the polygon's winding number
about the point is non–zero. If wind is 1, a pixel is inside if
the winding number is odd. Complementary values (0 or ~1) cause
outside pixels to be filled. The meaning of other values is undefined.
The polygon is closed with a line if necessary.
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r id[4] r[4*4]
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Cause the next read of the data file to return the image pixel
data corresponding to the rectangle r in image id.
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s dstid[4] srcid[4] fontid[4] dp[2*4] clipr[4*4] sp[2*4] n[2]
n*(index[2])
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Draw in the image dstid the text string specified by the n cache
indices into font fontid, starting with the upper left corner
at point p in image dstid. The image drawn is taken from image
srcid, translated to align sp in srcid with dp in dstid. All drawing
is confined to the clipping rectangle clipr in dstid.
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x dstid[4] srcid[4] fontid[4] dp[2*4] clipr[4*4] sp[2*4] n[2]
bgid[4] bp[2*4] n*(index[2])
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Like the string drawing s command, but fill the background of
each character with pixels from image bgid. The image bgid is
translated so that the point bp aligns with the point dp in dstid.
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S id[4] chan[4]
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Attach to the public screen with the specified id. It is an error
if the screen does not exist, is not public, or does not have
the channel descriptor chan for its associated image.
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t top[1] n[2] n*id[4]
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Send n windows to the top (if top is non–zero) or bottom (if top
is zero) of the window stack. The window is specified by the list
of n image ids are moved as a group, maintaining their own order
within the stack.
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v
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Flush changes from a soft screen, if any, to the display buffer.
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y id[4] r[4*4] buf[x*1]
Y id[4] r[4*4] buf[x*1]
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Replace the rectangle r of pixels in image id with the pixel data
in buf. The pixel data must be in the format dictated by id's
image channel descriptor (see image(6)). The y message uses uncompressed
data, while the Y message uses compressed data. In either case,
it is an error to include more data than
necessary.
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Reading the colormap returns the system color map used on 8–bit
displays. Each color map entry consists of a single line containing
four space–separated decimal strings. The first is an index into
the map, and the remaining three are the red, green, and blue
values associated with that index. The color map can be
changed by writing entries in the above format to the colormap
file. Note that changing the system color map does not change
the color map used for calculations involving m8 images, which
is immutable.
The refresh file is read–only. As windows owned by the client are
uncovered, if they cannot be refreshed by the server (such as
when they have refresh functions associated with them), a message
is made available on the refresh file reporting what needs to
be repainted by the client. The message has five decimal
integers formatted as in the ctl message: the image id of the
window and the coordinates of the rectangle that should be refreshed.
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