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Tk_CanvasTkwin(3)                           Tk Library Procedures                          Tk_CanvasTkwin(3)



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NAME
       Tk_CanvasTkwin,  Tk_CanvasGetCoord, Tk_CanvasDrawableCoords, Tk_CanvasSetStippleOrigin, Tk_CanvasWin-dowCoords, Tk_CanvasWindowCoords,
       dowCoords, Tk_CanvasEventuallyRedraw, Tk_CanvasTagsOption - utility procedures for canvas  type  man-agers managers
       agers

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 identifies a canvas widget.

       Tcl_Interp *interp (in/out)             Interpreter to use for error reporting.

       const char *string (in)                 Textual description 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.

       short *drawableXPtr (out)               Pointer  to  a  location in which to store an x coordinate in
                                               the space of the drawable currently being used  to  redisplay
                                               the canvas.

       short *drawableYPtr (out)               Pointer to a location in which to store a y coordinate 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 location in which to store the screen coordinate
                                               in the canvas window that corresponds to x.

       short *screenYPtr (out)                 Points to a location 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 redisplayed.

       int x2 (in)                             Right  edge  of the region that needs redisplay.  Only pixels
                                               to the left of this coordinate need to be redisplayed.

       int y2 (in)                             Bottom edge of the region that needs redisplay.  Only  pixels
                                               above this coordinate need to be redisplayed.
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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 dou-ble-precision double-precision
       ble-precision canvas coordinate.  If string is a valid coordinate description then  Tk_CanvasGetCoord
       stores  the corresponding 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_CanvasDrawableCoords computes the corre-sponding corresponding
       sponding pixel in the drawable that is currently being used for redisplay; it returns  those  coordi-nates coordinates
       nates  in *drawableXPtr and *drawableYPtr.  This procedure should not be invoked except during redis-play. redisplay.
       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_Canvas-SetStippleOrigin Tk_CanvasSetStippleOrigin
       SetStippleOrigin just before using gc to draw something;  after it is finished drawing, the type man-ager manager
       ager  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_CanvasDrawableCoords 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_CanvasEventuallyRedraw, since Tk can
       normally figure out when an item has changed and make the redisplay request on its behalf (this  hap-pens, happens,
       pens, 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 procedures in its Tk_ItemType; this could happen, for example, in an image item if
       the image is modified using image commands.

       Tk_CanvasTagsParseProc and Tk_CanvasTagsPrintProc are procedures that handle  the  -tags  option  for
       canvas  items.   The  code of a canvas type manager will not call these procedures 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 manager



Tk                                                   4.1                                   Tk_CanvasTkwin(3)