Tk_GetImage(3) Tk Library Procedures Tk_GetImage(3)_________________________________________________________________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 when-
ever image
content 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.
Tk 4.0 1
Tk_GetImage(3) Tk Library Procedures Tk_GetImage(3)
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).
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 spec-
ified 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-
Tk 4.0 2
Tk_GetImage(3) Tk Library Procedures Tk_GetImage(3)
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 dis-
play 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 call-
ing Tk_SizeOfImage: the width and height will be stored
in the locations given by widthPtr and heightPtr,
Tk 4.0 3
Tk_GetImage(3) Tk Library Procedures Tk_GetImage(3)
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 wid-
gets 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
Tk 4.0 4
