Provided by: tk8.6-doc_8.6.12-1build1_all 
NAME
Tk_CreatePhotoImageFormat - define new file format for photo images
SYNOPSIS
#include <tk.h>
Tk_CreatePhotoImageFormat(formatPtr)
ARGUMENTS
const Tk_PhotoImageFormat *formatPtr (in) Structure that defines the new file
format.
_________________________________________________________________________________________________
DESCRIPTION
Tk_CreatePhotoImageFormat is invoked to define a new file format for image data for use
with photo images. The code that implements an image file format is called an image file
format handler, or handler for short. The photo image code maintains a list of handlers
that can be used to read and write data to or from a file. Some handlers may also support
reading image data from a string or converting image data to a string format. The user
can specify which handler to use with the -format image configuration option or the
-format option to the read and write photo image subcommands.
An image file format handler consists of a collection of procedures plus a
Tk_PhotoImageFormat structure, which contains the name of the image file format and
pointers to six procedures provided by the handler to deal with files and strings in this
format. The Tk_PhotoImageFormat structure contains the following fields:
typedef struct Tk_PhotoImageFormat {
const char *name;
Tk_ImageFileMatchProc *fileMatchProc;
Tk_ImageStringMatchProc *stringMatchProc;
Tk_ImageFileReadProc *fileReadProc;
Tk_ImageStringReadProc *stringReadProc;
Tk_ImageFileWriteProc *fileWriteProc;
Tk_ImageStringWriteProc *stringWriteProc;
} Tk_PhotoImageFormat;
The handler need not provide implementations of all six procedures. For example, the
procedures that handle string data would not be provided for a format in which the image
data are stored in binary, and could therefore contain null characters. If any procedure
is not implemented, the corresponding pointer in the Tk_PhotoImageFormat structure should
be set to NULL. The handler must provide the fileMatchProc procedure if it provides the
fileReadProc procedure, and the stringMatchProc procedure if it provides the
stringReadProc procedure.
NAME
formatPtr->name provides a name for the image type. Once Tk_CreatePhotoImageFormat
returns, this name may be used in the -format photo image configuration and subcommand
option. The manual page for the photo image (photo(3tk)) describes how image file formats
are chosen based on their names and the value given to the -format option. The first
character of formatPtr->name must not be an uppercase character from the ASCII character
set (that is, one of the characters A-Z). Such names are used only for legacy interface
support (see below).
FILEMATCHPROC
formatPtr->fileMatchProc provides the address of a procedure for Tk to call when it is
searching for an image file format handler suitable for reading data in a given file.
formatPtr->fileMatchProc must match the following prototype:
typedef int Tk_ImageFileMatchProc(
Tcl_Channel chan,
const char *fileName,
Tcl_Obj *format,
int *widthPtr,
int *heightPtr,
Tcl_Interp *interp);
The fileName argument is the name of the file containing the image data, which is open for
reading as chan. The format argument contains the value given for the -format option, or
NULL if the option was not specified. If the data in the file appears to be in the format
supported by this handler, the formatPtr->fileMatchProc procedure should store the width
and height of the image in *widthPtr and *heightPtr respectively, and return 1. Otherwise
it should return 0.
STRINGMATCHPROC
formatPtr->stringMatchProc provides the address of a procedure for Tk to call when it is
searching for an image file format handler for suitable for reading data from a given
string. formatPtr->stringMatchProc must match the following prototype:
typedef int Tk_ImageStringMatchProc(
Tcl_Obj *data,
Tcl_Obj *format,
int *widthPtr,
int *heightPtr,
Tcl_Interp *interp);
The data argument points to the object containing the image data. The format argument
contains the value given for the -format option, or NULL if the option was not specified.
If the data in the string appears to be in the format supported by this handler, the
formatPtr->stringMatchProc procedure should store the width and height of the image in
*widthPtr and *heightPtr respectively, and return 1. Otherwise it should return 0.
FILEREADPROC
formatPtr->fileReadProc provides the address of a procedure for Tk to call to read data
from an image file into a photo image. formatPtr->fileReadProc must match the following
prototype:
typedef int Tk_ImageFileReadProc(
Tcl_Interp *interp,
Tcl_Channel chan,
const char *fileName,
Tcl_Obj *format,
PhotoHandle imageHandle,
int destX, int destY,
int width, int height,
int srcX, int srcY);
The interp argument is the interpreter in which the command was invoked to read the image;
it should be used for reporting errors. The image data is in the file named fileName,
which is open for reading as chan. The format argument contains the value given for the
-format option, or NULL if the option was not specified. The image data in the file, or a
subimage of it, is to be read into the photo image identified by the handle imageHandle.
The subimage of the data in the file is of dimensions width x height and has its top-left
corner at coordinates (srcX,srcY). It is to be stored in the photo image with its top-
left corner at coordinates (destX,destY) using the Tk_PhotoPutBlock procedure. The return
value is a standard Tcl return value.
STRINGREADPROC
formatPtr->stringReadProc provides the address of a procedure for Tk to call to read data
from a string into a photo image. formatPtr->stringReadProc must match the following
prototype:
typedef int Tk_ImageStringReadProc(
Tcl_Interp *interp,
Tcl_Obj *data,
Tcl_Obj *format,
PhotoHandle imageHandle,
int destX, int destY,
int width, int height,
int srcX, int srcY);
The interp argument is the interpreter in which the command was invoked to read the image;
it should be used for reporting errors. The data argument points to the image data in
object form. The format argument contains the value given for the -format option, or NULL
if the option was not specified. The image data in the string, or a subimage of it, is to
be read into the photo image identified by the handle imageHandle. The subimage of the
data in the string is of dimensions width x height and has its top-left corner at
coordinates (srcX,srcY). It is to be stored in the photo image with its top-left corner
at coordinates (destX,destY) using the Tk_PhotoPutBlock procedure. The return value is a
standard Tcl return value.
FILEWRITEPROC
formatPtr->fileWriteProc provides the address of a procedure for Tk to call to write data
from a photo image to a file. formatPtr->fileWriteProc must match the following
prototype:
typedef int Tk_ImageFileWriteProc(
Tcl_Interp *interp,
const char *fileName,
Tcl_Obj *format,
Tk_PhotoImageBlock *blockPtr);
The interp argument is the interpreter in which the command was invoked to write the
image; it should be used for reporting errors. The image data to be written are in memory
and are described by the Tk_PhotoImageBlock structure pointed to by blockPtr; see the
manual page FindPhoto(3tk) for details. The fileName argument points to the string giving
the name of the file in which to write the image data. The format argument contains the
value given for the -format option, or NULL if the option was not specified. The format
string can contain extra characters after the name of the format. If appropriate, the
formatPtr->fileWriteProc procedure may interpret these characters to specify further
details about the image file. The return value is a standard Tcl return value.
STRINGWRITEPROC
formatPtr->stringWriteProc provides the address of a procedure for Tk to call to translate
image data from a photo image into a string. formatPtr->stringWriteProc must match the
following prototype:
typedef int Tk_ImageStringWriteProc(
Tcl_Interp *interp,
Tcl_Obj *format,
Tk_PhotoImageBlock *blockPtr);
The interp argument is the interpreter in which the command was invoked to convert the
image; it should be used for reporting errors. The image data to be converted are in
memory and are described by the Tk_PhotoImageBlock structure pointed to by blockPtr; see
the manual page FindPhoto(3tk) for details. The data for the string should be put in the
interpreter interp result. The format argument contains the value given for the -format
option, or NULL if the option was not specified. The format string can contain extra
characters after the name of the format. If appropriate, the formatPtr->stringWriteProc
procedure may interpret these characters to specify further details about the image file.
The return value is a standard Tcl return value.
LEGACY INTERFACE SUPPORT
In Tk 8.2 and earlier, the definition of all the function pointer types stored in fields
of a Tk_PhotoImageFormat struct were incompatibly different. Legacy programs and
libraries dating from those days may still contain code that defines extended Tk photo
image formats using the old interface. The Tk header file will still support this legacy
interface if the code is compiled with the macro USE_OLD_IMAGE defined. Alternatively,
the legacy interfaces are used if the first character of formatPtr->name is an uppercase
ASCII character (A-Z), and explicit casts are used to forgive the type mismatch. For
example,
static Tk_PhotoImageFormat myFormat = {
"MyFormat",
(Tk_ImageFileMatchProc *) FileMatch,
NULL,
(Tk_ImageFileReadProc *) FileRead,
NULL,
NULL,
NULL
};
would define a minimal Tk_PhotoImageFormat that operates provide only file reading
capability, where FileMatch and FileRead are written according to the legacy interfaces of
Tk 8.2 or earlier.
Any stub-enabled extension providing an extended photo image format via the legacy
interface enabled by the USE_OLD_IMAGE macro that is compiled against Tk 8.5 headers and
linked against the Tk 8.5 stub library will produce a file that can be loaded only into
interps with Tk 8.5 or later; that is, the normal stub-compatibility rules. If a
developer needs to generate from such code a file that is loadable into interps with Tk
8.4 or earlier, they must use Tk 8.4 headers and stub libraries to do so.
Any new code written today should not make use of the legacy interfaces. Expect their
support to go away in Tk 9.
SEE ALSO
Tk_FindPhoto, Tk_PhotoPutBlock
KEYWORDS
photo image, image file