CrtImgType
Tk_CreateImageType(3) Tk Library Procedures Tk_CreateImageType(3)
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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 *type- |
Ptr (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 **typeP- |
trPtr (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
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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_CreateIm-
ageType. 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 proce-
dures 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 par-
ticular image, such as the values of the configuration options speci-
fied 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 simul-
taneously 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_CreateIm-
ageType returns, this name may be used in image create commands to cre-
ate images of the new type. If there already existed an image type by
this name then the new image type replaces the old one.
PORTABILITY
In Tk 8.2 and earlier, the createProc below had a different signature.
If you want to compile an image type using the old interface which
should still run on all Tcl/Tk versions, compile it with the flag
-DUSE_OLD_IMAGE. Further on, if you are using Stubs, you need to call
the function Tk_InitImageArgs(interp, argc, &argv) first in your cre-
ateProc. See below for a description of this function.
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 spec-
ified explicitly in the image command or generated automatically by the
image command. The objc and objv arguments describe all the configura-
tion 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 *mas-
terDataPtr, 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 dis-
play 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 dis-
play the image; drawable may be a pixmap rather than the window speci-
fied 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 associ-
ated 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 *mas-
terDataPtr 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 informa- |
tion about an image. For example, an image manager can use this proce- |
dure 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.
TK_INITIMAGEARGS
The function Tk_InitImageArgs converts the arguments of the createProc |
from objects to strings when necessary. When not using stubs, not using |
the old interface, or running under an older (pre-8.3) Tk version, this |
function has no effect. This function makes porting older image han- |
dlers to the new interface a lot easier: After running this function, |
the arguments are guaranteed to be in string format, no matter how Tk |
deliverd them. |
SEE ALSO |
Tk_ImageChanged, Tk_GetImage, Tk_FreeImage, Tk_RedrawImage, Tk_Size- |
OfImage |
KEYWORDS |
image manager, image type, instance, master |
Tk 8.3 Tk_CreateImageType(3)
