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 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
Tk 4.1 Tk_CanvasTkwin(3)
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