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GRAPHICS(3)		   Library Functions Manual		   GRAPHICS(3)

       Display,	 Point,	 Rectangle,  Cursor, initdraw, geninitdraw, drawerror,
       initdisplay, closedisplay, getdefont, getwindow,	gengetwindow, flushim-
       age,  bufimage,	lockdisplay,  unlockdisplay,  cursorswitch, cursorset,
       openfont, buildfont, freefont, Pfmt, Rfmt, strtochan, chantostr,	 chan-
       todepth - interactive graphics

       #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 *mousedir, 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)

       Font* getdefont(Display *d)

       int   flushimage(Display	*d, int	vis)

       int   bufimage(Display *d, int n)

       int   lockdisplay(Display *d)

       int   unlockdisplay(Display *d)

       int   getwindow(Display *d, int ref)

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

       int   scalesize(Display *d, int n)

       void  cursorswitch(Cursor *curs)

       void  cursorset(Point p)

       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

       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:

	      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(3)), such as  the
       display,	and is defined as:

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

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

       A Rectangle is a	rectangular area in an image.

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

       By definition, min.xaxmax.x and min.yaxmax.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-

       The Image data structure	is defined in draw(3).

       A Font is a set of character images, indexed  by	 runes	(see  utf(7)).
       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(3), 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(3) for more details.

       Buildfont  parses  the font description in the buffer desc, returning a
       Font* pointer that can be used by string	(see draw(3)) to draw  charac-
       ters  from the font.  Openfont does the same, but reads the description
       from the	named font.  Freefont frees a font.  In	contrast  to  Plan  9,
       font  names  in	Plan 9 from User Space are a small language describing
       the desired font.  See font(7) for details.

       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.

       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.	(See font(7) for a full	discussion  of
       font  syntaxes.)	 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 re-
       turn.  Its arguments are	the display pointer and	an error  string.   If
       errfun  is  nil,	the library provides a default,	called drawerror.  An-
       other effect of initdraw	is that	it installs print(3) 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;  mousedir	and  windir  are the directories holding the mouse and
       winname files; and ref specifies	the refresh function  to  be  used  to
       create the window, if running under rio(1) (see window(3)).

       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 Font structure from in-core  data	describing  a  default
       font.   None  of	these routines is needed by most programs, since init-
       draw 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 us-
       ing them	at a time.  Multi-process programs should set display->locking
       to  1,  to notify the library to	use a locking protocol for its own ac-
       cesses, and call	lockdisplay and	unlockdisplay around any calls to  the
       graphics	library	that will cause	messages to be sent to the display de-
       vice.  Initdraw and geninitdraw initialize the display  to  the	locked

       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  re-
       turns  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(3)).  The	resulting window will be created using
       the refresh method ref (see window(3)); this should  almost  always  be
       Refnone because rio provides backing store for the window.

       Getwindow  overwrites the global	variables screen, a pointer to the Im-
       age 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(3).	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;  sophisti-
       cated clients may use _screen to	make further subwindows.  If getwindow
       is being	called due to a	resizing of the	window,	the resize may be  ac-
       companied  by a change in screen	pixel density (DPI), in	which case the
       value of	the Display's dpi field	and any	open Font's height and	ascent
       fields  may  be	updated	during the call	to getwindow.  Programs	should
       discard any cached information about display or font sizes.  Gengetwin-
       dow's  extra  arguments	are the	full path of the window's winname file
       and pointers to be overwritten with the values of  the  `global'	 Image
       and Screen variables for	the new	window.

       Historically,  Plan  9  graphics	programs have used fixed-size graphics
       features	that assume a narrow range of display  densities,  around  100
       dpi:  pixels  (or  dots)	per inch.  The new field display->dpi contains
       the display's actual  density  if  known,  or  else  DefaultDPI	(100).
       Scalesize  scales  the  fixed pixel count n by display->dpi/DefaultDPI,
       rounding	appropriately.

       The mouse cursor	is always displayed.  The initial cursor is an	arrow.
       Cursorswitch  causes  the  argument  cursor to be displayed instead.  A
       zero argument causes a switch back  to  the  arrow  cursor.   Cursorset
       moves  the  mouse  cursor to position p,	provided (if in	a window) that
       the requesting program is executing in the current window and the mouse
       is within the window boundaries;	otherwise cursorset is a no-op.

       The   graphics	functions   described	in   draw(3),	allocimage(3),
       cachechars(3), and subfont(3) 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(3));
       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-

       The  functions  strtochan and chantostr convert between the channel de-
       scriptor	strings	used by	image(7) and the internal ulong	representation
       used  by	 the  graphics	protocol (see draw(3)'s	b message).  Chantostr
       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  str-
       tochan return 0 when presented with bad input.

       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	*/

       /usr/local/plan9/font/bit    directory of fonts


       rio(1),	addpt(3),  allocimage(3),  cachechars(3), subfont(3), draw(3),
       event(3), frame(3), print(3), window(3),	draw(3), image(7), font(7)

       An error	function may call errstr(3) for	further	diagnostics.

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

       These  manual  pages  contain  many  references	to  the	now-fictitious



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