Tk_CreateImageType (3)
define new kind of image
SYNOPSIS
#include <tk.h>
Tk_CreateImageType(typePtr)
ClientData
Tk_GetImageMasterData(interp, name, typePtrPtr)
ARGUMENTS
Tk_ImageType *typePtrPtr
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.
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 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.
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.
SEE ALSO
Tk_ImageChanged Tk_GetImage Tk_FreeImage Tk_RedrawImage Tk_SizeOfImage
KEYWORDS
image manager, image type, instance, master
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