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Tk_CanvasTkwin(3)     Tk Library Procedures	Tk_CanvasTkwin(3)

_________________________________________________________________

NAME
       Tk_CanvasTkwin,	 Tk_CanvasGetCoord,  Tk_CanvasDrawableCo-
       ords,  Tk_CanvasSetStippleOrigin,   Tk_CanvasWindowCoords,
       Tk_CanvasEventuallyRedraw,  Tk_CanvasTagsOption	- utility
       procedures for canvas type managers

SYNOPSIS
       #include <tk.h>

       Tk_Window
       Tk_CanvasTkwin(canvas)

       int
       Tk_CanvasGetCoord(interp, canvas, string, doublePtr)

       Tk_CanvasDrawableCoords(canvas, x, y, drawableXPtr, drawableYPtr)

       Tk_CanvasSetStippleOrigin(canvas, gc)

       Tk_CanvasWindowCoords(canvas, x, y, screenXPtr, screenYPtr)

       Tk_CanvasEventuallyRedraw(canvas, x1, y1, x2, y2)

       Tk_OptionParseProc *Tk_CanvasTagsParseProc;

       Tk_OptionPrintProc *Tk_CanvasTagsPrintProc;

ARGUMENTS
       Tk_Canvas     canvas	     (in)      A token that iden-
					       tifies	a  canvas
					       widget.

       Tcl_Interp    *interp	     (in/out)  Interpreter to use
					       for  error report-
					       ing.

       char	     *string	     (in)      Textual	 descrip-
					       tion  of	 a canvas
					       coordinate.

       double	     *doublePtr	     (out)     Points to place to
					       store  a converted
					       coordinate.

       double	     x		     (in)      An x coordinate in
					       the  space  of the
					       canvas.

       double	     y		     (in)      A y coordinate  in
					       the  space  of the
					       canvas.

Tk			       4.1				1

Tk_CanvasTkwin(3)     Tk Library Procedures	Tk_CanvasTkwin(3)

       short	     *drawableXPtr   (out)     Pointer to a loca-
					       tion  in	 which to
					       store an x coordi-
					       nate  in the space
					       of  the	 drawable
					       currently    being
					       used to	redisplay
					       the canvas.

       short	     *drawableYPtr   (out)     Pointer to a loca-
					       tion in	which  to
					       store  a y coordi-
					       nate in the  space
					       of   the	 drawable
					       currently    being
					       used  to redisplay
					       the canvas.

       GC	     gc		     (out)     Graphics	  context
					       to modify.

       short	     *screenXPtr     (out)     Points  to a loca-
					       tion in	which  to
					       store  the  screen
					       coordinate in  the
					       canvas window that
					       corresponds to  x.

       short	     *screenYPtr     (out)     Points  to a loca-
					       tion in	which  to
					       store  the  screen
					       coordinate in  the
					       canvas window that
					       corresponds to  y.

       int	     x1		     (in)      Left  edge  of the
					       region that  needs
					       redisplay.    Only
					       pixels  at  or  to
					       the  right of this
					       coordinate need to
					       be redisplayed.

       int	     y1		     (in)      Top  edge  of  the
					       region that  needs
					       redisplay.    Only
					       pixels at or below
					       this    coordinate
					       need to be  redis-
					       played.

       int	     x2		     (in)      Right  edge of the
					       region that  needs
					       redisplay.    Only

Tk			       4.1				2

Tk_CanvasTkwin(3)     Tk Library Procedures	Tk_CanvasTkwin(3)

					       pixels to the left
					       of this coordinate
					       need to be  redis-
					       played.

       int	     y2		     (in)      Bottom edge of the
					       region that  needs
					       redisplay.    Only
					       pixels above  this
					       coordinate need to
					       be redisplayed.
_________________________________________________________________

DESCRIPTION
       These procedures are called by  canvas  type  managers  to
       perform various utility functions.

       Tk_CanvasTkwin  returns	the  Tk_Window	associated with a
       particular canvas.

       Tk_CanvasGetCoord translates a string specification  of	a
       coordinate  (such  as  2p or 1.6c) into a double-precision
       canvas  coordinate.   If	 string	 is  a	valid  coordinate
       description  then Tk_CanvasGetCoord stores the correspond-
       ing canvas coordinate at *doublePtr  and	 returns  TCL_OK.
       Otherwise it stores an error message in interp->result and
       returns TCL_ERROR.

       Tk_CanvasDrawableCoords is called by type managers  during
       redisplay  to compute where to draw things.  Given x and y
       coordinates in the space of the canvas, Tk_CanvasDrawable-
       Coords  computes	 the  corresponding pixel in the drawable
       that is currently being used  for  redisplay;  it  returns
       those  coordinates  in  *drawableXPtr  and  *drawableYPtr.
       This procedure should not be invoked except during  redis-
       play.

       Tk_CanvasSetStippleOrigin  is  also used during redisplay.
       It sets the stipple origin in gc so  that  stipples  drawn
       with  gc in the current offscreen pixmap will line up with
       stipples drawn with origin (0,0) in  the	 canvas's  actual
       window.	 Tk_CanvasSetStippleOrigin  is needed in order to
       guarantee that stipple patterns line up properly when  the
       canvas  is  redisplayed	in  small pieces.  Redisplays are
       carried out in double-buffered fashion where  a	piece  of
       the  canvas  is	redrawn	 in  an offscreen pixmap and then
       copied back onto the screen.  In this approach the stipple
       origins	in  graphics  contexts need to be adjusted during
       each redisplay to compensate for the position of the  off-
       screen pixmap relative to the window.  If an item is being
       drawn with stipples,  its  type	manager	 typically  calls
       Tk_CanvasSetStippleOrigin  just	before	using  gc to draw
       something;  after it is finished drawing, the type manager

Tk			       4.1				3

Tk_CanvasTkwin(3)     Tk Library Procedures	Tk_CanvasTkwin(3)

       calls  XSetTSOrigin  to	restore	 the origin in gc back to
       (0,0) (the restore is needed because graphics contexts are
       shared, so they cannot be modified permanently).

       Tk_CanvasWindowCoords  is  similar to Tk_CanvasDrawableCo-
       ords except that it returns coordinates	in  the	 canvas's
       window  on  the	screen, instead of coordinates in an off-
       screen pixmap.

       Tk_CanvasEventuallyRedraw may be invoked by a type manager
       to  inform  Tk  that  a	portion	 of  a canvas needs to be
       redrawn.	 The x1, y1, x2, and  y2  arguments  specify  the
       region  that  needs  to be redrawn, in canvas coordinates.
       Type managers rarely need to invoke Tk_CanvasEventuallyRe-
       draw,  since  Tk	 can normally figure out when an item has
       changed and make the redisplay request on its behalf (this
       happens,	 for example whenever Tk calls a configureProc or
       scaleProc).  The only time that a type  manager	needs  to
       call  Tk_CanvasEventuallyRedraw	is if an item has changed
       on its own without being invoked through one of the proce-
       dures  in its Tk_ItemType; this could happen, for example,
       in an image item if the image is modified using image com-
       mands.

       Tk_CanvasTagsParseProc and Tk_CanvasTagsPrintProc are pro-
       cedures that handle the -tags  option  for  canvas  items.
       The  code of a canvas type manager won't call these proce-
       dures directly, but will use their addresses to	create	a
       Tk_CustomOption structure for the -tags option.	 The code
       typically looks like this:
	      static Tk_CustomOption tagsOption = {Tk_CanvasTagsParseProc,
		Tk_CanvasTagsPrintProc, (ClientData) NULL
	      };

	      static Tk_ConfigSpec configSpecs[] = {
		...
		{TK_CONFIG_CUSTOM, "-tags", (char *) NULL, (char *) NULL,
		   (char *) NULL, 0, TK_CONFIG_NULL_OK, &tagsOption},
		...
	      };

KEYWORDS
       canvas, focus, item type, redisplay, selection, type  man-
       ager

Tk			       4.1				4

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