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.
- const 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 (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 (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 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 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_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:
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