Tk_CreateImageType(3)
Tk_CreateImageType(3) Tk Library Procedures Tk_CreateImageType(3)
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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
Tk_ImageType *typePtr (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 **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
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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,
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Tk_CreateImageType(3) Tk Library Procedures Tk_CreateImageType(3)
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 pro-
vided 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 sub-
sections 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 com-
mand. 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 possi-
ble for a single image to appear simultaneously in multiple
widgets, or even multiple times in the same widget. Furth-
ermore, 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 usu-
ally 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.
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Tk_CreateImageType(3) Tk Library Procedures Tk_CreateImageType(3)
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 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 pro-
cedure. 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 *master-
DataPtr, 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
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Tk_CreateImageType(3) Tk Library Procedures Tk_CreateImageType(3)
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 pro-
totype:
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 pix-
map 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 proto-
type:
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.
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Tk_CreateImageType(3) Tk Library Procedures Tk_CreateImageType(3)
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 sup-
port 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 migra-
tion 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
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Tk_CreateImageType(3) Tk Library Procedures Tk_CreateImageType(3)
empty comment. Any stub-enabled extension providing an
extended image type via the legacy interface that is com-
piled 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
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