libtk/doc/GetImage.3

#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
.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 changeProc.
.AP Tk_Image image in
Token for image instance; must have been returned by a previous
call to Tk_GetImage.
.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
Tk_GetImage or a pixmap compatible with that window.
.AP 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.
.AP 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.
.AP "int" widthPtr out
Store width of image (in pixels) here.
.AP "int" heightPtr out
Store height of image (in pixels) here.
E
 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.

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:
.CS
typedef void Tk_ImageChangedProc(
 ClientData clientData,
 int x,
 int y,
 int width,
 int height,
 int imageWidth,
 int imageHeight);
.CE
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