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GRAPHICS(2)                   System Calls Manual                  GRAPHICS(2)



NAME
       Display,  Point,  Rectangle,  Cursor, initdraw, geninitdraw, drawerror,
       initdisplay, closedisplay, getdefont, getwindow, gengetwindow, flushim‐
       age,  bufimage,  lockdisplay, unlockdisplay, openfont, buildfont, free‐
       font, Pfmt,  Rfmt,  strtochan,  chantostr,  chantodepth  -  interactive
       graphics

SYNOPSIS
       #include <u.h>
       #include <libc.h>
       #include <draw.h>
       #include <cursor.h>

       int   initdraw(void (*errfun)(Display*, char*), char *font,
                char *label)

       int   geninitdraw(char *devdir, void(*errfun)(Display*, char*),
                char *font, char *label, char *windir, int ref)

       int   newwindow(char *str)

       void  drawerror(Display *d, char *msg)

       Display*initdisplay(char *devdir, char *win, void(*errfun)(Display*, char*))

       void  closedisplay(Display *d)

       Subfont*getdefont(Display *d)

       int   flushimage(Display *d, int vis)

       uchar*bufimage(Display *d, int n)

       void  lockdisplay(Display *d)

       void  unlockdisplay(Display *d)

       int   getwindow(Display *d, int ref)

       int   gengetwindow(Display *d, char *winname,
                Image **ip, Screen **sp, int ref)

       Font* openfont(Display *d, char *name)

       Font* buildfont(Display *d, char *desc, char *name)

       void  freefont(Font *f)

       int   Pfmt(Fmt*)

       int   Rfmt(Fmt*)

       ulong strtochan(char *s)

       char* chantostr(char *s, ulong chan)

       int   chantodepth(ulong chan)

       extern Display *display

       extern Image   *screen

       extern Screen   *_screen

       extern Font    *font

DESCRIPTION
       A  Display  structure  represents  a connection to the graphics device,
       draw(3), holding all graphics resources associated with the connection,
       including in particular raster image data in use by the client program.
       The structure is defined (in part) as:

              typedef
              struct Display
              {
                    ...
                    void      (*error)(Display*, char*);
                    ...
                    Image     *black;
                    Image     *white;
                    Image     *opaque;
                    Image     *transparent;
                    Image     *image;
                    Font      *defaultfont;
                    Subfont   *defaultsubfont;
                    ...
              };

       A Point is a location in an Image (see below and draw(2)), such as  the
       display, and is defined as:

              typedef
              struct Point {
                    int x;
                    int y;
              } Point;

       The  coordinate  system  has x increasing to the right and y increasing
       down.

       A Rectangle is a rectangular area in an image.

              typedef
              struct Rectangle {
                    Point min;      /* upper left */
                    Point max;      /* lower right */
              } Rectangle;

       By definition, min.xâ¤max.x and min.yâ¤max.y.  By convention, the right
       (maximum  x)  and bottom (maximum y) edges are excluded from the repre‐
       sented rectangle, so abutting rectangles  have  no  points  in  common.
       Thus,  max  contains the coordinates of the first point beyond the rec‐
       tangle.

       The Image data structure is defined in draw(2).

       A Font is a set of character images, indexed  by  runes  (see  utf(6)).
       The  images are organized into Subfonts, each containing the images for
       a small, contiguous set of runes.  The detailed format  of  these  data
       structures,  which are described in detail in cachechars(2), is immate‐
       rial for most applications.  Font and Subfont  structures  contain  two
       interrelated fields: the distance from the top of the highest character
       (actually the top of the image holding all the characters) to the base‐
       line,  and  the  distance  from the top of the highest character to the
       bottom of the lowest character (and hence, the interline spacing).  See
       cachechars(2) for more details.

       Buildfont  parses  the font description in the buffer desc, returning a
       Font* pointer that can be used by string (see draw(2)) to draw  charac‐
       ters  from the font.  Openfont does the same, but reads the description
       from the named file.  Freefont frees a font.  The convention for naming
       font files is:

              /lib/font/bit/name/range.size.font

       where size is approximately the height in pixels of the lower case let‐
       ters (without ascenders or descenders).  Range gives some indication of
       which characters will be available: for example ascii, latin1, euro, or
       unicode.  Euro includes most European languages, punctuation marks, the
       International Phonetic Alphabet, etc., but no Oriental languages.  Uni‐
       code includes every character for which appropriate-sized images  exist
       on the system.

       A Cursor is defined:

              typedef struct
              Cursor {
                    Point offset;
                    uchar clr[2*16];
                    uchar set[2*16];
              } Cursor;

       The  arrays  are  arranged in rows, two bytes per row, left to right in
       big-endian order to give 16 rows of 16 bits each.   A  cursor  is  dis‐
       played  on  the  screen by adding offset to the current mouse position,
       using clr as a mask to draw white at the pixels where clr is  one,  and
       then  drawing  black  at  the  pixels  where set is one.  Setcursor and
       moveto (see mouse(2)) and esetcursor and emoveto (see event(2))  change
       the cursor image and its location on the screen.

       The routine initdraw connects to the display; it returns -1 if it fails
       and sets the error string.  Initdraw sets up the global variables  dis‐
       play  (the  Display  structure representing the connection), screen (an
       Image representing the display memory itself or, if rio(1) is  running,
       the  client's window), and font (the default font for text).  The argu‐
       ments to initdraw include a label, which is written  to  /dev/label  if
       non-nil  so that it can be used to identify the window when hidden (see
       rio(1)).  The font is created by reading the named font file.  If  font
       is  null,  initdraw  reads  the  file named in the environment variable
       $font; if $font is not set, it imports the  default  (usually  minimal)
       font  from  the operating system.  The global font will be set to point
       to the resulting Font structure.  The errfun  argument  is  a  graphics
       error function to call in the event of a fatal error in the library; it
       must never return.  Its arguments are the display pointer and an  error
       string.  If errfun is nil, the library provides a default, called draw‐
       error.  Another effect of initdraw is that it installs print(2) formats
       Pfmt and Rfmt as and for printing Points and Rectangles.

       The  geninitdraw  function provides a less automated way to establish a
       connection, for programs that wish to  connect  to  multiple  displays.
       Devdir is the name of the directory containing the device files for the
       display (if nil, default /dev); errfun, font, and label are as in init‐
       draw; windir is the directory holding the winname files; and ref speci‐
       fies the refresh function to be used to create the window,  if  running
       under rio(1) (see window(2)).

       The  function newwindow may be called before initdraw or geninitdraw to
       cause the program to occupy a newly created  window  rather  than  take
       over  the one in which it is running when it starts.  The str argument,
       if non-null, is concatenated to the string "new " that is used to  cre‐
       ate  the  window (see rio(4)).  For example, newwindow("-hide -dy 100")
       will cause the program to run in a newly  created,  hidden  window  100
       pixels high.

       Initdisplay  is  part of geninitdraw; it sets up the display structures
       but does not allocate any fonts or call getwindow.  The  arguments  are
       similar to those of initdraw; win names the directory, default /dev, in
       which the files associated with the window reside.   Closedisplay  dis‐
       connects  the display and frees the associated data structures.  Getde‐
       font builds a Subfont structure from in-core data describing a  default
       subfont.   None  of  these  routines  is needed by most programs, since
       initdraw calls them as needed.

       The data structures associated with the display must be protected in  a
       multi-process  program,  because  they  assume only one process will be
       using them at a time.  Multi-process programs should set display->lock‐
       ing  to  1, to notify the library to use a locking protocol for its own
       accesses, and call lockdisplay and unlockdisplay around  any  calls  to
       the graphics library that will cause messages to be sent to the display
       device.  Initdraw and geninitdraw initialize the display to the  locked
       state.

       Getwindow  returns a pointer to the window associated with the applica‐
       tion; it is called automatically by initdraw to  establish  the  screen
       pointer but must be called after each resizing of the window to restore
       the library's connection to the window.  If  rio  is  not  running,  it
       returns  display->image; otherwise it negotiates with rio by looking in
       /dev/winname to find the name of the window and opening it using named‐
       image  (see allocimage(2)).  The resulting window will be created using
       the refresh method ref (see window(2)); this should  almost  always  be
       Refnone because rio provides backing store for the window.

       Getwindow  overwrites  the  global  variables  screen, a pointer to the
       Image defining the window (or the overall display, if no window  system
       is running); and _screen, a pointer to the Screen representing the root
       of the window's hierarchy. (See  window(2).   The  overloading  of  the
       screen word is an unfortunate historical accident.)  Getwindow arranges
       that screen point to the portion  of  the  window  inside  the  border;
       sophisticated clients may use _screen to make further subwindows.  Pro‐
       grams desiring multiple independent windows may use the  mechanisms  of
       rio(4)  to  create more windows (usually by a fresh mount of the window
       sytem in a directory other than /dev), then use gengetwindow to connect
       to  them.  Gengetwindow's extra arguments are the full path of the win‐
       dow's winname file and pointers to be overwritten with  the  values  of
       the `global' Image and Screen variables for the new window.

       The   graphics   functions   described   in   draw(2),   allocimage(2),
       cachechars(2), and subfont(2) are implemented by  writing  commands  to
       files  under  /dev/draw  (see draw(3)); the writes are buffered, so the
       functions may not take effect immediately.  Flushimage flushes the buf‐
       fer,  doing  all  pending graphics operations.  If vis is non-zero, any
       changes are also copied from the `soft screen' (if any) in  the  driver
       to  the  visible  frame buffer.  The various allocation routines in the
       library flush automatically, as does the event package (see  event(2));
       most programs do not need to call flushimage.  It returns -1 on error.

       Bufimage  is  used to allocate space for n bytes in the display buffer.
       It is used by all the graphics routines to send messages  to  the  dis‐
       play.

       The  functions  strtochan  and  chantostr  convert  between the channel
       descriptor strings used by image(6) and the internal ulong  representa‐
       tion  used  by  the graphics protocol (see draw(3)'s b message).  Chan‐
       tostr writes at most nine bytes into the buffer pointed  at  by  s  and
       returns  s on success, 0 on failure.  Chantodepth returns the number of
       bits per pixel used by the format specified by chan.  Both  chantodepth
       and strtochan return 0 when presented with bad input.

EXAMPLES
       To reconnect to the window after a resize event,

              if(getwindow(display, Refnone) < 0)
                    sysfatal("resize failed: %r");

       To create and set up a new rio(1) window,

              Image *screen2;
              Screen *_screen2;

              srvwsys = getenv("wsys");
              if(srvwsys == nil)
                    sysfatal("can't find $wsys: %r");
              rfork(RFNAMEG); /* keep mount of rio private */

              fd = open(srvwsys, ORDWR);
              if(fd < 0)
                    sysfatal("can't open $wsys: %r");

              /* mount creates window; see rio(4) */
              if(mount(fd, -1, "/tmp", MREPL, "new -dx 300-dy 200") < 0)
                    sysfatal("can't mount new window: %r");
              if(gengetwindow(display, "/tmp/winname",
                 &screen2, &_screen2, Refnone) < 0)
                    sysfatal("resize failed: %r");

              /* now open /tmp/cons, /tmp/mouse */
              ...

FILES
       /lib/font/bit    directory of fonts

SOURCE
       /sys/src/libdraw

SEE ALSO
       rio(1),  addpt(2),  allocimage(2),  cachechars(2), subfont(2), draw(2),
       event(2), frame(2), print(2),  window(2),  draw(3),  rio(4),  image(6),
       font(6)

DIAGNOSTICS
       An error function may call errstr(2) for further diagnostics.

BUGS
       The  names  clr  and  set  in  the Cursor structure are reminders of an
       archaic color map and might be  more  appropriately  called  white  and
       black.



                                                                   GRAPHICS(2)