DRAW-DISPLAY(2)                                   DRAW-DISPLAY(2)

          Display - connection to draw device

          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):
              cmap2rgb:    fn(d: self ref Display, c: int):
                           (int, int, int);
              cmap2rgba:   fn(d: self ref Display, c: int):

          Chans: adt
             mk:    fn(s: string): Chans;
             text:  fn(c: self Chans): string;
             eq:    fn(c: self Chans, d: Chans): int;

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     DRAW-DISPLAY(2)                                   DRAW-DISPLAY(2)

             depth: fn(c: self Chans): int;

          The Display type represents a connection to a 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 Image objects must be allocated through Display mem-
          ber functions.  Graphics operations that use multiple Image
          objects may not mix images from different Displays.

          The pixel channel structure of an 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 colour(6), and internally by a value of the Chans adt,
          which is used when allocating new images in the calls below.
          Draw defines a set of constants of type Chans for common
          channel types: GREY1, GREY2 and GREY8 for greyscale (depths
          1, 2 and 8); CMAP8 for 8-bit colour(8) colour-mapped images;
          RGB16 for 16-bit r5g6b5 colour images; RGB24 for 24-bit
          colour; and RGBA32 for 24-bit colour with alpha channel.
          Chans has the following operations:

                    Return the Chans value corresponding to the chan-
                    nel format string s (see image(6) for the syntax
                    of s).

          c.depth() Return the depth in bits of c. The result is 0 if
                    c is invalid; in particular, Chans.mk(s).depth()
                    is zero if s is invalid.

          c.text()  Return the format string corresponding to c.

          c.eq(d)   Return true if d has the same channel structure as
                    c; return false otherwise.

          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 sig-
          nificant 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.

          Display itself has the following components:

          image     The visible contents of the display; draw on image
                    to change the display.

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     DRAW-DISPLAY(2)                                   DRAW-DISPLAY(2)

          white, black
                    Replicated images of a single pixel, either all
                    ones (white) or all zeroes (black).

          opaque, transparent
                    Replicated images of a single pixel, either all
                    ones (fully opaque) or all zeroes (fully transpar-
                    ent).  Used as mattes for basic graphical opera-

                    Attach to a new display, represented by the
                    draw(3) device mounted in the specified dev direc-
                    tory.  If dev is the empty string, /dev is used.
                    The return value is nil if the allocation fails.

                    After allocating a Display object, the application
                    should spawn a process to call startrefresh; this
                    thread will receive and process window refresh
                    events from the device.

                    Create a locally addressable pointer to a public
                    Screen; see display-screen(2).

          d.newimage(r, chans, repl, rgba)
                    Allocate an off-screen Image.  The arguments sup-
                    ply values for the Image's r, chans, and repl, and
                    an initial pixel value rgba in 32-bit RGBA format,
                    used to paint the image when created.  It can be
                    Draw->Transparent to create a fully transparent
                    image to draw on to form an arbitrarily-shaped
                    image or matte.  If it is Draw->Nofill, the image
                    is not initialised.  The image's clipr is initial-
                    ized to r.

                    Creates a single-pixel, replicated off-screen
                    image of the specified colour, expressed in 32-bit
                    RGBA format.  The Draw module defines constants
                    for several dozen colours:

                         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;

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     DRAW-DISPLAY(2)                                   DRAW-DISPLAY(2)

                         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;

                    The special values Draw->Opaque (fully opaque) and
                    Draw->Transparent (fully transparent) are useful
                    as the pixel values for Display.newimage when
                    forming a matte.  The special value Draw->Nofill
                    tells Display.newimage not to paint a new image
                    with any colour, leaving it uninitialised.

          d.colormix(one, three)
                    Allocate background colours.  On true color dis-
                    plays, 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 dis-
                    plays, it returns a 2×2 replicated image with one
                    pixel coloured one and the other three with three
                    (after translation through the colour map).  This
                    simulates a wider range of tones than can be rep-
                    resented by a single pixel value on a colour-
                    mapped display.

          d.rgb(red, green, 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).

                    Returns a reference to the image published as name
                    on display d by Image.name (see draw-image(2)).
                    This allows unrelated processes to share the image

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     DRAW-DISPLAY(2)                                   DRAW-DISPLAY(2)

                    (eg, a window manager and client).

                    Read an image description from the named file and
                    return an Image holding the picture.  See image(6)
                    for more information about image files.

                    Analogous to open, but from an open file descrip-
                    tor rather than a named file.

          d.writeimage(fd, i)
                    Complement of readimage: write an image file rep-
                    resenting i to the open file descriptor.

          d.rgb2cmap(red, green, blue)
                    Return the rgbv colour map index (see 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).

                    Return the colour triple (red, blue, green) corre-
                    sponding to colour map index c.

                    Return the 32-bit RGBA representation of the
                    colour corresponding to colour map index c. The
                    alpha component is always 255 (fully opaque).

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