Tk_CreateImageType(3) Tk Library Procedures Tk_CreateImageType(3) ______________________________________________________________________________
NAME
Tk_CreateImageType, Tk_GetImageMasterData, Tk_GetImageModelData,
Tk_InitImageArgs - define new kind of image
SYNOPSIS
#include <tk.h>
Tk_CreateImageType(typePtr)
ClientData
Tk_GetImageMasterData(interp, name, typePtrPtr)
ClientData |
Tk_GetImageModelData(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_CreateIm-
ageType. 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 proce-
dures 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 model; it contains overall information about a partic-
ular image, such as the values of the configuration options specified
in an image create command. There will usually be one of these struc-
tures 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 simul-
taneously 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_CreateIm-
ageType returns, this name may be used in image create commands to cre-
ate 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 model,
ClientData *modelDataPtr);
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 spec-
ified explicitly in the image command or generated automatically by the
image command. The objc and objv arguments describe all the configura-
tion options for the new image (everything after the name argument to
image). The model 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 model data structure for the
new image. createProc may store an arbitrary one-word value at *model-
DataPtr, which will be passed back to the image manager when other
callbacks are invoked. Typically the value is a pointer to the model
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 modelData);
The tkwin argument identifies the window in which the image will be
used and modelData is the value returned by createProc when the image
model was created. getProc will usually create a data structure for
the new instance, including such things as the resources needed to dis-
play 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 dis-
play the image; drawable may be a pixmap rather than the window speci-
fied 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 associ-
ated 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 modelData);
The modelData argument will be the same as the value stored in *model-
DataPtr by createProc when the image was created. deleteProc should
release any resources associated with the image.
TK_GETIMAGEMODELDATA
The procedure Tk_GetImageMasterData may be invoked to retrieve informa-
tion about an image. For example, an image manager can use this proce-
dure to locate its image model 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
model data structure). If no such image exists then NULL is returned
and NULL is stored at *typePtrPtr.
Tk_GetImageModelData is synonym for Tk_GetImageMasterData |
LEGACY INTERFACE SUPPORT
In Tk 8.2 and earlier, the definition of Tk_ImageCreateProc was incom-
patibly different, with the following prototype:
typedef int Tk_ImageCreateProc(
Tcl_Interp *interp,
char *name,
int argc,
char **argv,
Tk_ImageType *typePtr,
Tk_ImageMaster model,
ClientData *modelDataPtr);
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.
Tk_ImageModel is synonym for Tk_ImageMaster |
When the USE_OLD_IMAGE legacy support is enabled, you may see the rou-
tine 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 rou-
tine, 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 gen-
erate 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 inter-
faces. Expect their support to go away in Tk 9.
SEE ALSO
Tk_ImageChanged(3), Tk_GetImage(3), Tk_FreeImage(3), Tk_RedrawImage(3),
Tk_SizeOfImage(3)
KEYWORDS
image manager, image type, instance, model
Tk 8.5 Tk_CreateImageType(3)
tk 8.6.11 - Generated Fri Jan 22 15:34:42 CST 2021