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.
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
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
(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
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