Tk_GetImage(3tk) Tk Library Procedures Tk_GetImage(3tk)
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NAME
Tk_GetImage, Tk_RedrawImage, Tk_SizeOfImage, Tk_FreeImage - use an im-
age 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 mes-
sage.
Tk_Window tkwin (in) Window in which image
will be used.
const char *name (in) Name of image.
Tk_ImageChangedProc *changeProc (in) Procedure for Tk to in-
voke whenever image con-
tent or size changes.
ClientData clientData (in) One-word value for Tk to
pass to changeProc.
Tk_Image image (in) 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 (mea-
sured in pixels from the
image's upper-left cor-
ner).
int imageY (in) Y-coordinate of upper-
left corner of region of
image to redisplay (mea-
sured in pixels from the
image's upper-left cor-
ner).
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.
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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 in-
stance of the image. If the image does not exist then Tk_GetImage re-
turns NULL and leaves an error message in interpreter interp's result.
When a widget wishes to actually display an image it must call Tk_Re-
drawImage, 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_Size-
OfImage: the width and height will be stored in the locations given by
widthPtr and heightPtr, respectively.
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 redis-
play themselves. The changeProc and clientData arguments to Tk_GetIm-
age are used for this purpose. changeProc will be called by Tk when-
ever a change occurs in the image; it must match the following proto-
type:
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 ar-
gument 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 im-
ageHeight give the image's (new) size.
SEE ALSO
Tk_CreateImageType
KEYWORDS
images, redisplay
Tk 4.0 Tk_GetImage(3tk)
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