Tk_GetImage(3Tk)Tk_GetImage(3Tk)NAME
Tk_GetImage, Tk_RedrawImage, Tk_SizeOfImage, Tk_FreeImage - use an image
in a widget
SYNOPSIS
#include <tk.h>
Tk_Image
Tk_GetImage(interp, tkwin, name, changeProc, clientData)
Tk_RedrawImage(image, imageX, imageY, width, height, drawable,
drawableX, drawableY)
Tk_SizeOfImage(image, widthPtr, heightPtr)
Tk_FreeImage(image)ARGUMENTS
Tcl_Interp *interp (in) Place to leave error
message.
Tk_Window tkwin (in) Window in which image will
be used.
char *name (in) Name of image.
Tk_ImageChangedProc *changeProc (in) Procedure for Tk to invoke
whenever image content or
size changes.
ClientData clientData (in) One-word value for Tk to
pass to changeProc.
Tk_Image image Token for image instance;
must have been returned by
a previous call to
Tk_GetImage.
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).
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).
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Tk_GetImage(3Tk)Tk_GetImage(3Tk)
int width ((in)) Width of region of image to
redisplay.
int height ((in)) Height of region of image
to redisplay.
Drawable drawable (in) Where to display image.
Must either be window
specified to Tk_GetImage or
a pixmap compatible with
that window.
int drawableX (in) Where to display image in
drawable: this is the x-
coordinate in drawable
where x-coordinate imageX
of the image should be
displayed.
int drawableY (in) Where to display image in
drawable: this is the y-
coordinate in drawable
where y-coordinate imageY
of the image should be
displayed.
int widthPtr (out) Store width of image (in
pixels) here.
int heightPtr (out) Store height of image (in
pixels) here.
DESCRIPTION
These procedures are invoked by widgets that wish to display images.
Tk_GetImage is invoked by a widget when it first decides to display an
image. name gives the name of the desired image and tkwin identifies the
window where the image will be displayed. Tk_GetImage 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 Tk_GetImage returns NULL and
leaves an error message in interp->result.
When a widget wishes to actually display an image it must call
Tk_RedrawWidget, identifying the image (image), a region within the image
to redisplay (imageX, imageY, width, and height), and a place to display
the image (drawable, drawableX, and drawableY). Tk will then invoke the
appropriate image manager, which will display the requested portion of
the image before returning.
A widget can find out the dimensions of an image by calling
Tk_SizeOfImage: the width and height will be stored in the locations
given by widthPtr and heightPtr, respectively.
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Tk_GetImage(3Tk)Tk_GetImage(3Tk)
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 Tk_FreeImage to release the image instance. The
widget should never again use the image token after passing it to
Tk_FreeImage. There must be exactly one call to Tk_FreeImage for each
call to Tk_GetImage.
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 changeProc and clientData arguments to Tk_GetImage are
used for this purpose. changeProc will be called by Tk whenever a change
occurs in the image; it must match the following prototype:
typedef void Tk_ImageChangedProc(
ClientData clientData,
int x,
int y,
int width,
int height,
int imageWidth,
int imageHeight);
The clientData argument to changeProc is the same as the clientData
argument to Tk_GetImage. It is usually a pointer to the widget record
for the widget or some other data structure managed by the widget. The
arguments x, y, width, and height 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 imageWidth and imageHeight
give the image's (new) size.
SEE ALSO
Tk_CreateImageType
KEYWORDS
images, redisplay
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