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
Place to leave error message. Window in which image will be used.
Name of image. Procedure for Tk to invoke whenever image content or
size changes. One-word value for Tk to pass to changeProc. Token for
image instance; must have been returned by a previous call to
Tk_GetImage. X-coordinate of upper-left corner of region of image to
redisplay (measured in pixels from the image's upper-left corner). Y-
coordinate of upper-left corner of region of image to redisplay (mea-
sured in pixels from the image's upper-left corner). Width of region
of image to redisplay. Height of region of image to redisplay. Where
to display image. Must either be window specified to Tk_GetImage or a
pixmap compatible with that window. Where to display image in draw-
able: this is the x-coordinate in drawable where x-coordinate imageX of
the image should be displayed. Where to display image in drawable:
this is the y-coordinate in drawable where y-coordinate imageY of the
image should be displayed. Store width of image (in pixels) here.
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 does not 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_RedrawImage, 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 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(3)
KEYWORDS
images, redisplay
Tk 4.0 Tk_GetImage(3)
GetImage 8.5.4 - Generated Sat Aug 23 16:25:41 CDT 2008