Tk_CanvasTkwin(3) Tk (4.1) Tk_CanvasTkwin(3)
_________________________________________________________________
NAME
Tk_CanvasTkwin, Tk_CanvasGetCoord, Tk_CanvasDrawableCoords,
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
identifies a canvas
widget.
Tcl_Interp *interp (in/out) Interpreter to use
for error reporting.
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.
Page 1 (printed 2/26/99)
Tk_CanvasTkwin(3) Tk (4.1) Tk_CanvasTkwin(3)
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
Page 2 (printed 2/26/99)
Tk_CanvasTkwin(3) Tk (4.1) Tk_CanvasTkwin(3)
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.
_________________________________________________________________
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 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 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 redisplay.
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
Page 3 (printed 2/26/99)
Tk_CanvasTkwin(3) Tk (4.1) Tk_CanvasTkwin(3)
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
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 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 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 won't 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
Page 4 (printed 2/26/99)
