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 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
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
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_CanvasDrawableCoords computes the corresponding pixel
in the drawable that is currently being used for redis-
play; 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 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
(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 coordi-
nates 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 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