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
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 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,
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 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