Tk_CreateImageType(3) Tk Library Procedures Tk_CreateImageType(3)_________________________________________________________________NAME
Tk_CreateImageType - define new kind of image
SYNOPSIS
#include <tk.h>
Tk_CreateImageType(typePtr)ARGUMENTS
Tk_ImageType *typePtr (in) Structure that defines
the new type of image.
_________________________________________________________________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
Tk 4.0 1
Tk_CreateImageType(3) Tk Library Procedures Tk_CreateImageType(3)
possible for a single image to appear simultaneously 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_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 argu-
ment 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 struc-
ture 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.
Tk 4.0 2
Tk_CreateImageType(3) Tk Library Procedures Tk_CreateImageType(3)
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 draw-
able 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.
Tk 4.0 3
Tk_CreateImageType(3) Tk Library Procedures Tk_CreateImageType(3)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
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 associ-
ated with the image.
SEE ALSO
Tk_ImageChanged, Tk_GetImage, Tk_FreeImage, Tk_RedrawIm-
age, Tk_SizeOfImage
KEYWORDS
image manager, image type, instance, master
Tk 4.0 4
