path: root/doc/GetImage.3

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'\" RCS: @(#) $Id: GetImage.3,v 1.4 1999/04/21 21:53:22 rjohnson Exp $
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.so man.macros
.TH Tk_GetImage 3 4.0 Tk "Tk Library Procedures"
.BS
.SH NAME
Tk_GetImage, Tk_RedrawImage, Tk_SizeOfImage, Tk_FreeImage \- use an image in a widget
.SH SYNOPSIS
.nf
\fB#include <tk.h>\fR
.sp
Tk_Image
\fBTk_GetImage\fR(\fIinterp, tkwin, name, changeProc, clientData\fR)
.sp
\fBTk_RedrawImage\fR(\fIimage, imageX, imageY, width, height, drawable, drawableX, drawableY\fR)
.sp
\fBTk_SizeOfImage\fR(\fIimage, widthPtr, heightPtr\fR)
.sp
\fBTk_FreeImage\fR(\fIimage\fR)
.SH ARGUMENTS
.AS Tk_ImageChangedProc *changeProc
.AP Tcl_Interp *interp in
Place to leave error message.
.AP Tk_Window tkwin in
Window in which image will be used.
.AP char *name in
Name of image.
.AP Tk_ImageChangedProc *changeProc in
Procedure for Tk to invoke whenever image content or size changes.
.AP ClientData clientData in
One-word value for Tk to pass to \fIchangeProc\fR.
.AP Tk_Image image in
Token for image instance;  must have been returned by a previous
call to \fBTk_GetImage\fR.
.AP int imageX in
X-coordinate of upper-left corner of region of image to redisplay
(measured in pixels from the image's upper-left corner).
.AP int imageY in
Y-coordinate of upper-left corner of region of image to redisplay
(measured in pixels from the image's upper-left corner).
.AP "int" width (in)
Width of region of image to redisplay.
.AP "int" height (in)
Height of region of image to redisplay.
.AP Drawable drawable in
Where to display image.  Must either be window specified to
\fBTk_GetImage\fR or a pixmap compatible with that window.
.AP int drawableX in
Where to display image in \fIdrawable\fR: this is the x-coordinate
in \fIdrawable\fR where x-coordinate \fIimageX\fR of the image
should be displayed.
.AP int drawableY in
Where to display image in \fIdrawable\fR: this is the y-coordinate
in \fIdrawable\fR where y-coordinate \fIimageY\fR of the image
should be displayed.
.AP "int" widthPtr out
Store width of \fIimage\fR (in pixels) here.
.AP "int" heightPtr out
Store height of \fIimage\fR (in pixels) here.
.BE

.SH DESCRIPTION
.PP
These procedures are invoked by widgets that wish to display images.
\fBTk_GetImage\fR is invoked by a widget when it first decides to
display an image.
\fIname\fR gives the name of the desired image and \fItkwin\fR
identifies the window where the image will be displayed.
\fBTk_GetImage\fR looks up the image in the table of existing
images and returns a token for a new instance of the image.
If the image doesn't exist then \fBTk_GetImage\fR returns NULL
and leaves an error message in \fIinterp->result\fR.
.PP
When a widget wishes to actually display an image it must
call \fBTk_RedrawImage\fR, identifying the image (\fIimage\fR),
a region within the image to redisplay (\fIimageX\fR, \fIimageY\fR,
\fIwidth\fR, and \fIheight\fR), and a place to display the
image (\fIdrawable\fR, \fIdrawableX\fR, and \fIdrawableY\fR).
Tk will then invoke the appropriate image manager, which will
display the requested portion of the image before returning.
.PP
A widget can find out the dimensions of an image by calling
\fBTk_SizeOfImage\fR:  the width and height will be stored
in the locations given by \fIwidthPtr\fR and \fIheightPtr\fR,
respectively.
.PP
When a widget is finished with an image (e.g., the widget is
being deleted or it is going to use a different image instead
of the current one), it must call \fBTk_FreeImage\fR to
release the image instance.
The widget should never again use the image token after passing
it to \fBTk_FreeImage\fR.
There must be exactly one call to \fBTk_FreeImage\fR for each
call to \fBTk_GetImage\fR.
.PP
If the contents or size of an image changes, then any widgets
using the image will need to find out about the changes so that
they can redisplay themselves.
The \fIchangeProc\fR and \fIclientData\fR arguments to
\fBTk_GetImage\fR are used for this purpose.
\fIchangeProc\fR will be called by Tk whenever a change occurs
in the image;  it must match the following prototype:
.CS
typedef void Tk_ImageChangedProc(
	ClientData \fIclientData\fR,
	int \fIx\fR,
	int \fIy\fR,
	int \fIwidth\fR,
	int \fIheight\fR,
	int \fIimageWidth\fR,
	int \fIimageHeight\fR);
.CE
The \fIclientData\fR argument to \fIchangeProc\fR is the same as the
\fIclientData\fR argument to \fBTk_GetImage\fR.
It is usually a pointer to the widget record for the widget or
some other data structure managed by the widget.
The arguments \fIx\fR, \fIy\fR, \fIwidth\fR, and \fIheight\fR
identify a region within the image that must be redisplayed;
they are specified in pixels measured from the upper-left
corner of the image.
The arguments \fIimageWidth\fR and \fIimageHeight\fR give
the image's (new) size.

.SH "SEE ALSO"
Tk_CreateImageType

.SH KEYWORDS
images, redisplay