focal (3) Tk_CreateImageType.3tk.gz
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