Tk_CreatePhotoImageFormat(3) Tk Library ProceduresTk_CreatePhotoImageFormat(3)______________________________________________________________________________NAMETk_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.
_________________________________________________________________DESCRIPTIONTk_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 han‐
dler to deal with files and strings in this format. The Tk_PhotoImage‐
Format 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 pro‐
vided 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 proce‐
dure.
NAME
formatPtr->name provides a name for the image type. Once Tk_CreatePho‐
toImageFormat returns, this name may be used in the -format photo image
configuration and subcommand option. The manual page for the photo
image (photo(n)) describes how image file formats are chosen based on
their names and the value given to the -format option. The first char‐
acter 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 sup‐
ported 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 suit‐
able 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 for‐
matPtr->stringMatchProc procedure should store the width and height of
the image in *widthPtr and *heightPtr respectively, and return 1. Oth‐
erwise 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. for‐
matPtr->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 dimen‐
sions 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 proce‐
dure. 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. for‐
matPtr->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 imageHan‐
dle. 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. for‐
matPtr->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_PhotoIm‐
ageBlock structure pointed to by blockPtr; see the manual page Find‐
Photo(3) for details. The fileName argument points to the string giv‐
ing 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 for‐
matPtr->fileWriteProc procedure may interpret these characters to spec‐
ify further details about the image file. The return value is a stan‐
dard 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. for‐
matPtr->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(3) 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 spec‐
ified. The format string can contain extra characters after the name
of the format. If appropriate, the formatPtr->stringWriteProc proce‐
dure 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 dif‐
ferent. 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. Alterna‐
tively, the legacy interfaces are used if the first character of for‐
matPtr->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 com‐
piled 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 inter‐
faces. Expect their support to go away in Tk 9.
SEE ALSO
Tk_FindPhoto, Tk_PhotoPutBlock
KEYWORDS
photo image, image file
Tk 8.5 Tk_CreatePhotoImageFormat(3)
