ref: 948870cffe2572efb68ef0b3873b36238fb53263
dir: /man/2/draw-display/
.TH DRAW-DISPLAY 2
.SH NAME
Display \-
connection to draw device
.SH SYNOPSIS
.EX
include "draw.m";
draw := load Draw Draw->PATH;
Display: adt
{
image: ref Image;
white: ref Image;
black: ref Image;
opaque: ref Image;
transparent: ref Image;
allocate: fn(dev: string): ref Display;
startrefresh:fn(d: self ref Display);
publicscreen:fn(d: self ref Display, id: int):
ref Screen;
newimage: fn(d: self ref Display,
r: Rect, chans: Chans,
repl, rgba: int):
ref Image;
color: fn(d: self ref Display, rgba: int):
ref Image;
colormix: fn(d: self ref Display, one: int, three: int):
ref Image;
rgb: fn(d: self ref Display, red, green, blue: int):
ref Image;
namedimage: fn(d: self ref Display, name: string):
ref Image;
open: fn(d: self ref Display, name: string):
ref Image;
readimage: fn(d: self ref Display, fd: ref Sys->FD):
ref Image;
writeimage: fn(d: self ref Display, fd: ref Sys->FD,
i: ref Image): int;
rgb2cmap: fn(d: self ref Display, red, green, blue: int):
int;
cmap2rgb: fn(d: self ref Display, c: int):
(int, int, int);
cmap2rgba: fn(d: self ref Display, c: int):
int;
};
Chans: adt
{
mk: fn(s: string): Chans;
text: fn(c: self Chans): string;
eq: fn(c: self Chans, d: Chans): int;
depth: fn(c: self Chans): int;
};
.EE
.SH DESCRIPTION
The
.B Display
type represents a connection to a
.IR draw (3)
device.
This device is the external representation of a physical
display, such as a CRT, and its associated memory.
It contains the storage for all images,
even invisible ones, so all
.B Image
objects must be allocated
through
.B Display
member functions.
Graphics operations that use multiple
.B Image
objects may not mix images from different
.BR Displays .
.PP
The pixel channel structure of an
.B Image
is determined when the image is allocated (including the image allocated by the system
to represent a physical display).
This structure is described externally by a channel format string,
described in
.IR colour (6),
and internally by a value of the
.B Chans
adt,
which is used when allocating new images in the calls below.
.B Draw
defines a set of constants of type
.B Chans
for common channel types:
.BR GREY1 ,
.BR GREY2
and
.BR GREY8
for greyscale (depths 1, 2 and 8);
.BR CMAP8
for 8-bit
.IR rgbv (8)
colour-mapped images;
.BR RGB16
for 16-bit
.B r5g6b5
colour images;
.BR RGB24
for 24-bit colour;
and
.BR RGBA32
for 24-bit colour with alpha channel.
.B Chans
has the following operations:
.TP 10
.BI Chans.mk( s )
Return the
.B Chans
value corresponding to the channel format string
.I s
(see
.IR image (6)
for the syntax of
.IR s ).
.TP 10
.IB c .depth()
Return the depth in bits of
.IR c .
The result is 0 if
.I c
is invalid; in particular,
.BI Chans.mk( s ).depth()
is zero if
.I s
is invalid.
.TP
.IB c .text()
Return the format string corresponding to
.IR c .
.TP
.IB c .eq( d )
Return true if
.I d
has the same channel structure as
.IR c ;
return false otherwise.
.PP
Colours in the calls below are specified as 32-bit integers (`32-bit RGBA format') containing
red, green, blue and alpha components as 8-bit values, in order
from most to least significant byte.
The 8-bit colour component values express illumination, ranging from 0 (no colour)
to 255 (saturated).
For the alpha component, 0 is fully transparent, and 255 is fully opaque.
.PP
.B Display
itself has the following components:
.PP
.TP 10
.B image
The visible contents of the display;
draw on
.B image
to change the display.
.TP
.BR white ", " black
Replicated images of a single pixel,
either all ones (white) or all zeroes (black).
.TP
.BR opaque ", " transparent
Replicated images of a single pixel,
either all ones (fully opaque) or all zeroes (fully transparent).
Used as mattes for
basic graphical operations.
.TP
.BI allocate( dev )
Attach to a new display, represented by the
.IR draw (3)
device mounted in the specified
.I dev
directory.
If
.I dev
is the empty string,
.B /dev
is used.
The return value is
.B nil
if the allocation fails.
.TP
.IB d .startrefresh()
After allocating a
.B Display
object, the application should spawn a process to call
.BR startrefresh ;
this thread will receive and process window refresh events
from the device.
.TP
.IB d .publicscreen( id )
Create a locally addressable pointer to a public
.BR Screen ;
see \f2display-screen\fP(2).
.TP
.IB d .newimage( r\fP,\fP\ chans\fP,\fP\ repl\fP,\fP\ rgba )
Allocate an off-screen
.BR Image .
The arguments supply values for the
.BR Image 's
.BR r ,
.BR chans ,
and
.BR repl ,
and an initial pixel value
.I rgba
in 32-bit RGBA format,
used to paint the image
when created.
It can be
.B Draw\->Transparent
to create a fully transparent image to draw on to form an
arbitrarily-shaped image or matte.
If it is
.BR Draw\->Nofill ,
the image is not initialised.
The image's
.B clipr
is initialized to
.BR r .
.TP
.IB d .color( rgba )
Creates a single-pixel,
replicated off-screen image of the specified colour,
expressed in 32-bit RGBA format.
The
.B Draw
module defines constants for several dozen colours:
.RS
.IP
.EX
Opaque: con int 16rFFFFFFFF;
Transparent: con int 16r00000000;
Black: con int 16r000000FF;
White: con int 16rFFFFFFFF;
Red: con int 16rFF0000FF;
Green: con int 16r00FF00FF;
Blue: con int 16r0000FFFF;
Cyan: con int 16r00FFFFFF;
Magenta: con int 16rFF00FFFF;
Yellow: con int 16rFFFF00FF;
Grey: con int 16rEEEEEEFF;
Paleyellow: con int 16rFFFFAAFF;
Darkyellow: con int 16rEEEE9EFF;
Darkgreen: con int 16r448844FF;
Palegreen: con int 16rAAFFAAFF;
Medgreen: con int 16r88CC88FF;
Darkblue: con int 16r000055FF;
Palebluegreen: con int 16rAAFFFFFF;
Paleblue: con int 16r0000BBFF;
Bluegreen: con int 16r008888FF;
Greygreen: con int 16r55AAAAFF;
Palegreygreen: con int 16r9EEEEEFF;
Yellowgreen: con int 16r99994CFF;
Medblue: con int 16r000099FF;
Greyblue: con int 16r005DBBFF;
Palegreyblue: con int 16r4993DDFF;
Purpleblue: con int 16r8888CCFF;
Notacolor: con int 16rFFFFFF00;
Nofill: con Notacolor;
.EE
.PP
The special values
.BR Draw\->Opaque
(fully opaque)
and
.BR Draw\->Transparent
(fully transparent)
are useful as the pixel values for
.B Display.newimage
when forming a matte.
The special value
.B Draw\->Nofill
tells
.B Display.newimage
not to paint a new image with any colour, leaving it uninitialised.
.RE
.TP
.IB d .colormix( one\fP,\fP\ three )
Allocate background colours.
On true color displays, it returns a 1×1 replicated image whose pixel is the result of mixing the two
colours in a one to three ratio;
both colours are expressed in 32-bit RGBA format.
On 8-bit color-mapped displays, it returns a 2×2 replicated image
with one pixel coloured
.I one
and the other three
with
.I three
(after translation through the colour map).
This simulates a wider range of tones than can
be represented by a single pixel value on a colour-mapped display.
.TP
.IB d .rgb( red\fP,\fP\ green\fP,\fP\ blue )
Uses the values of red, green, and blue to create
a single-pixel replicated image of that colour.
The values are intensities that range from 0 (no colour) to 255 (saturated).
The alpha component is always 255 (fully opaque).
.TP
.IB d .namedimage ( name )
Returns a reference to the image published as
.I name
on display
.I d
by
.B Image.name
(see
.IR draw-image (2)).
This allows unrelated processes to share the image (eg, a window manager and client).
.TP
.IB d .open( name )
Read an image
description from the named
file and return an
.B Image
holding the picture.
See
.IR image (6)
for more information about image files.
.TP
.IB d .readimage( fd )
Analogous to
.BR open ,
but from an open file descriptor rather than a named file.
.TP
.IB d .writeimage( fd\fP,\fP\ i )
Complement of
.BR readimage :
write an image file representing
.B i
to the open file descriptor.
.TP
.IB d .rgb2cmap( red\fP,\fP\ green\fP,\fP\ blue )
Return the
.I rgbv
colour map index (see
.IR colour (6))
of the colour that best matches
the given colour triple. The values of the components range from
0 (no colour) to 255 (saturated).
.TP
.IB d .cmap2rgb( c )
Return the colour triple (red, blue, green) corresponding to colour
map index
.IR c .
.TP
.IB d .cmap2rgba( c )
Return the 32-bit RGBA representation of the colour corresponding to colour
map index
.IR c .
The alpha component is always 255 (fully opaque).
.ig
.TP
.IB d .cursor(\fIi\fP,\ \fIp\fP)
Set the current cursor.
If
.I i
is the image of the current display,
then the graphics cursor will be set
to its default value, otherwise
.I i
must be an image with ldepth 0
and the following rules apply: the size of the
cursor will be half the horizontal height of
.I i
(subject to system-dependent restrictions on cursor
size). The top half and the bottom half of the image
are treated as two independent masks. When the
cursor is drawn, pixels congruent with non-zero bits
in the top half are cleared
and then pixels congruent with non-zero bits in the
bottom half are set.
.I P
gives the offset added to the mouse position when drawing
the cursor image.
.TP
.IB d .cursorset(\fIp\fP)
Set the position of the mouse cursor to
.IR p .
.SH BUGS
The interface to
.B cursor
does not allow the use of colour mouse cursors,
even on systems that allow them. The interface is likely
to change in this respect.
..