tk_createimagetype(3)

NAME

Tk_CreateImageType, Tk_GetImageMasterData, Tk_InitIm
ageArgs - define new kind of image

SYNOPSIS

#include <tk.h>
Tk_CreateImageType(typePtr)
ClientData
Tk_GetImageMasterData(interp, name, typePtrPtr)
Tk_InitImageArgs(interp, argc, argvPtr)

ARGUMENTS

Tk_ImageType *type_
Ptr (in)

Structure that
defines the new
type of image.
Must be static: a
pointer to this
structure is
retained by the
image code.

Tcl_Interp *interp (in)

Interpreter in
which image was
created.

CONST
char *name (in)

Name of existing
image.

Tk_ImageType **typeP_
trPtr (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 {

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 wid
get. 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.

PORTABILITY

In Tk 8.2 and earlier, the createProc below had a differ
ent signature. If you want to compile an image type using
the old interface which should still run on all Tcl/Tk
versions, compile it with the flag -DUSE_OLD_IMAGE. Fur
ther on, if you are using Stubs, you need to call the
function Tk_InitImageArgs(interp, argc, &argv) first in
your createProc. See below for a description of this func
tion.

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,
char *name,
int objc,
Tcl_Obj *CONST objv[],
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 argu
ment 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 struc ture 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 interp->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 draw_ able 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 exam ple, 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 associ ated 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 Client
Data 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.

TK_INITIMAGEARGS

The function Tk_InitImageArgs converts the arguments of the createProc from objects to strings when necessary. When not using stubs, not using the old interface, or run
ning under an older (pre-8.3) Tk version, this function
has no effect. This function makes porting older image
handlers to the new interface a lot easier: After running
this function, the arguments are guaranteed to be in
string format, no matter how Tk deliverd them.

SEE ALSO

Tk_ImageChanged, Tk_GetImage, Tk_FreeImage, Tk_RedrawIm
age, Tk_SizeOfImage

KEYWORDS

image manager, image type, instance, master

Tk 8.3 Tk_CreateImageType(3)