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Tk Library Procedures Tk_CanvasTkwin(3TK)

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NAME

Tk_CanvasTkwin, Tk_CanvasGetCoord, Tk_CanvasDrawableCoords,

Tk_CanvasSetStippleOrigin, Tk_CanvasWindowCoords,

Tk_CanvasEventuallyRedraw, Tk_CanvasTagsOption - utility

procedures for canvas type managers

SYNOPSIS

#include

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 identi-

fies a canvas widget.

Tcl_Interp *interp (in/out) Interpreter to use

for error reporting. CONST char *string (in) Textual description

of a canvas coordi-

nate. 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. Tk Last change: 4.1 1

Tk Library Procedures Tk_CanvasTkwin(3TK)

short *drawableXPtr (out) Pointer to a loca-

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 coordinate in the space of the drawable currently being used to

redisplay the can-

vas. GC gc (out) Graphics context to modify. short *screenXPtr (out) Points to a location in which to store

the screen coordi-

nate in the canvas window that corresponds to x. short *screenYPtr (out) Points to a location in which to store

the screen coordi-

nate 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 coor-

dinate 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 Tk Last change: 4.1 2

Tk Library Procedures Tk_CanvasTkwin(3TK)

redisplay. Only pixels to the

left of this coordi-

nate 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 per-

form various utility functions.

Tk_CanvasTkwin returns the Tk_Window associated with a par-

ticular canvas.

Tk_CanvasGetCoord translates a string specification of a

coordinate (such as 2p or 1.6c) into a double-precision can-

vas coordinate. If string is a valid coordinate description

then Tk_CanvasGetCoord stores the corresponding canvas coor-

dinate 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 com-

pensate for the position of the off-screen pixmap relative

to the window. If an item is being drawn with stipples, its Tk Last change: 4.1 3

Tk Library Procedures Tk_CanvasTkwin(3TK)

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 exam-

ple 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 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

ATTRIBUTES

See attributes(5) for descriptions of the following attri-

butes: Tk Last change: 4.1 4

Tk Library Procedures Tk_CanvasTkwin(3TK)

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| ATTRIBUTE TYPE | ATTRIBUTE VALUE|

|____________________|__________________|_

| Availability | runtime/tk-8 |

|____________________|__________________|_

| Interface Stability| Uncommitted |

|____________________|_________________|

NOTES Source for Tk is available on http://opensolaris.org. Tk Last change: 4.1 5