Provided by: tk8.6-doc_8.6.10-1_all 
NAME
Tk_CreateImageType, Tk_GetImageMasterData, Tk_InitImageArgs - define new kind of image
SYNOPSIS
#include <tk.h>
Tk_CreateImageType(typePtr)
ClientData
Tk_GetImageMasterData(interp, name, typePtrPtr)
Tk_InitImageArgs(interp, argc, argvPtr)
ARGUMENTS
const Tk_ImageType *typePtr (in) Structure that defines the new type of image.
For Tk 8.4 and earlier this must be static: a
pointer to this structure is retained by the
image code. In Tk 8.5, this limitation was
relaxed.
Tcl_Interp *interp (in) Interpreter in which image was created.
const char *name (in) Name of existing image.
Tk_ImageType **typePtrPtr (out) Points to word in which to store a pointer to
type information for the given image, if it
exists.
int argc (in) Number of arguments
char ***argvPtr (in/out) Pointer to argument list
_________________________________________________________________________________________________
DESCRIPTION
Tk_CreateImageType is invoked to define a new kind of image. An image type corresponds to
a particular value of the type argument for the image create command. There may exist any
number of different image types, and new types may be defined dynamically by calling
Tk_CreateImageType. For example, there might be one type for 2-color bitmaps, another for
multi-color images, another for dithered images, another for video, and so on.
The code that implements a new image type is called an image manager. It consists of a
collection of procedures plus three different kinds of data structures. The first data
structure is a Tk_ImageType structure, which contains the name of the image type and
pointers to five procedures provided by the image manager to deal with images of this
type:
typedef struct Tk_ImageType {
const char *name;
Tk_ImageCreateProc *createProc;
Tk_ImageGetProc *getProc;
Tk_ImageDisplayProc *displayProc;
Tk_ImageFreeProc *freeProc;
Tk_ImageDeleteProc *deleteProc;
} Tk_ImageType;
The fields of this structure will be described in later subsections of this entry.
The second major data structure manipulated by an image manager is called an image master;
it contains overall information about a particular image, such as the values of the
configuration options specified in an image create command. There will usually be one of
these structures for each invocation of the image create command.
The third data structure related to images is an image instance. There will usually be
one of these structures for each usage of an image in a particular widget. It is possible
for a single image to appear simultaneously in multiple widgets, or even multiple times in
the same widget. Furthermore, different instances may be on different screens or
displays. The image instance data structure describes things that may vary from instance
to instance, such as colors and graphics contexts for redisplay. There is usually one
instance structure for each -image option specified for a widget or canvas item.
The following subsections describe the fields of a Tk_ImageType in more detail.
NAME
typePtr->name provides a name for the image type. Once Tk_CreateImageType returns, this
name may be used in image create commands to create images of the new type. If there
already existed an image type by this name then the new image type replaces the old one.
CREATEPROC
typePtr->createProc provides the address of a procedure for Tk to call whenever image
create is invoked to create an image of the new type. typePtr->createProc must match the
following prototype:
typedef int Tk_ImageCreateProc(
Tcl_Interp *interp,
const char *name,
int objc,
Tcl_Obj *const objv[],
const Tk_ImageType *typePtr,
Tk_ImageMaster master,
ClientData *masterDataPtr);
The interp argument is the interpreter in which the image command was invoked, and name is
the name for the new image, which was either specified explicitly in the image command or
generated automatically by the image command. The objc and objv arguments describe all
the configuration options for the new image (everything after the name argument to image).
The master argument is a token that refers to Tk's information about this image; the
image manager must return this token to Tk when invoking the Tk_ImageChanged procedure.
Typically createProc will parse objc and objv and create an image master data structure
for the new image. createProc may store an arbitrary one-word value at *masterDataPtr,
which will be passed back to the image manager when other callbacks are invoked.
Typically the value is a pointer to the master data structure for the image.
If createProc encounters an error, it should leave an error message in the interpreter
result and return TCL_ERROR; otherwise it should return TCL_OK.
createProc should call Tk_ImageChanged in order to set the size of the image and request
an initial redisplay.
GETPROC
typePtr->getProc is invoked by Tk whenever a widget calls Tk_GetImage to use a particular
image. This procedure must match the following prototype:
typedef ClientData Tk_ImageGetProc(
Tk_Window tkwin,
ClientData masterData);
The tkwin argument identifies the window in which the image will be used and masterData is
the value returned by createProc when the image master was created. getProc will usually
create a data structure for the new instance, including such things as the resources
needed to display the image in the given window. getProc returns a one-word token for the
instance, which is typically the address of the instance data structure. Tk will pass
this value back to the image manager when invoking its displayProc and freeProc
procedures.
DISPLAYPROC
typePtr->displayProc is invoked by Tk whenever an image needs to be displayed (i.e.,
whenever a widget calls Tk_RedrawImage). displayProc must match the following prototype:
typedef void Tk_ImageDisplayProc(
ClientData instanceData,
Display *display,
Drawable drawable,
int imageX,
int imageY,
int width,
int height,
int drawableX,
int drawableY);
The instanceData will be the same as the value returned by getProc when the instance was
created. display and drawable indicate where to display the image; drawable may be a
pixmap rather than the window specified to getProc (this is usually the case, since most
widgets double-buffer their redisplay to get smoother visual effects). imageX, imageY,
width, and height identify the region of the image that must be redisplayed. This region
will always be within the size of the image as specified in the most recent call to
Tk_ImageChanged. drawableX and drawableY indicate where in drawable the image should be
displayed; displayProc should display the given region of the image so that point
(imageX, imageY) in the image appears at (drawableX, drawableY) in drawable.
FREEPROC
typePtr->freeProc contains the address of a procedure that Tk will invoke when an image
instance is released (i.e., when Tk_FreeImage is invoked). This can happen, for example,
when a widget is deleted or a image item in a canvas is deleted, or when the image
displayed in a widget or canvas item is changed. freeProc must match the following
prototype:
typedef void Tk_ImageFreeProc(
ClientData instanceData,
Display *display);
The instanceData will be the same as the value returned by getProc when the instance was
created, and display is the display containing the window for the instance. freeProc
should release any resources associated with the image instance, since the instance will
never be used again.
DELETEPROC
typePtr->deleteProc is a procedure that Tk invokes when an image is being deleted (i.e.
when the image delete command is invoked). Before invoking deleteProc Tk will invoke
freeProc for each of the image's instances. deleteProc must match the following
prototype:
typedef void Tk_ImageDeleteProc(
ClientData masterData);
The masterData argument will be the same as the value stored in *masterDataPtr by
createProc when the image was created. deleteProc should release any resources associated
with the image.
TK_GETIMAGEMASTERDATA
The procedure Tk_GetImageMasterData may be invoked to retrieve information about an image.
For example, an image manager can use this procedure to locate its image master data for
an image. If there exists an image named name in the interpreter given by interp, then
*typePtrPtr is filled in with type information for the image (the typePtr value passed to
Tk_CreateImageType when the image type was registered) and the return value is the
ClientData value returned by the createProc when the image was created (this is typically
a pointer to the image master data structure). If no such image exists then NULL is
returned and NULL is stored at *typePtrPtr.
LEGACY INTERFACE SUPPORT
In Tk 8.2 and earlier, the definition of Tk_ImageCreateProc was incompatibly different,
with the following prototype:
typedef int Tk_ImageCreateProc(
Tcl_Interp *interp,
char *name,
int argc,
char **argv,
Tk_ImageType *typePtr,
Tk_ImageMaster master,
ClientData *masterDataPtr);
Legacy programs and libraries dating from those days may still contain code that defines
extended Tk image types using the old interface. The Tk header file will still support
this legacy interface if the code is compiled with the macro USE_OLD_IMAGE defined.
When the USE_OLD_IMAGE legacy support is enabled, you may see the routine Tk_InitImageArgs
in use. This was a migration tool used to create stub-enabled extensions that could be
loaded into interps containing all versions of Tk 8.1 and later. Tk 8.5 no longer
provides this routine, but uses a macro to convert any attempted calls of this routine
into an empty comment. Any stub-enabled extension providing an extended image type via
the legacy interface that is compiled against Tk 8.5 headers and linked against the Tk 8.5
stub library will produce a file that can be loaded only into interps with Tk 8.5 or
later; that is, the normal stub-compatibility rules. If a developer needs to generate
from such code a file that is loadable into interps with Tk 8.4 or earlier, they must use
Tk 8.4 headers and stub libraries to do so.
Any new code written today should not make use of the legacy interfaces. Expect their
support to go away in Tk 9.
SEE ALSO
Tk_ImageChanged, Tk_GetImage, Tk_FreeImage, Tk_RedrawImage, Tk_SizeOfImage
KEYWORDS
image manager, image type, instance, master