Tk_CreateImageType(3Tk)Tk_CreateImageType(3Tk)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 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.
Page 1
Tk_CreateImageType(3Tk)Tk_CreateImageType(3Tk)
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
Page 2
Tk_CreateImageType(3Tk)Tk_CreateImageType(3Tk)
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.
Page 3
Tk_CreateImageType(3Tk)Tk_CreateImageType(3Tk)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.
SEE ALSO
Tk_ImageChanged, Tk_GetImage, Tk_FreeImage, Tk_RedrawImage,
Tk_SizeOfImage
KEYWORDS
image manager, image type, instance, master
Page 4
