Tk_CreateImageType(3) Tk (8.0) Tk_CreateImageType(3)
_________________________________________________________________
NAME
Tk_CreateImageType, Tk_GetImageMasterData - define new kind
of image
SYNOPSIS
#include <tk.h>
Tk_CreateImageType(typePtr)
ClientData
Tk_GetImageMasterData(interp, name, typePtrPtr) |
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. |
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.
_________________________________________________________________
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.
Page 1 (printed 2/26/99)
Tk_CreateImageType(3) Tk (8.0) Tk_CreateImageType(3)
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
Page 2 (printed 2/26/99)
Tk_CreateImageType(3) Tk (8.0) Tk_CreateImageType(3)
image of the new type. typePtr->createProc must match the
following prototype:
typedef int Tk_ImageCreateProc(
Tcl_Interp *interp,
char *name,
int argc,
char **argv,
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 argc
and argv 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 argc and argv
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 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.
Page 3 (printed 2/26/99)
Tk_CreateImageType(3) Tk (8.0) Tk_CreateImageType(3)
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
Page 4 (printed 2/26/99)
Tk_CreateImageType(3) Tk (8.0) Tk_CreateImageType(3)
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.
SEE ALSO
Tk_ImageChanged, Tk_GetImage, Tk_FreeImage, Tk_RedrawImage,
Tk_SizeOfImage
KEYWORDS
image manager, image type, instance, master
Page 5 (printed 2/26/99)
