Tk_CreatePhotoImageFormat(3) Tk Library ProceduresTk_CreatePhotoImageFormat(3)______________________________________________________________________________NAME
Tk_CreatePhotoImageFormat - define new file format for photo images
SYNOPSIS
#include <tk.h>
#include <tkPhoto.h>
Tk_CreatePhotoImageFormat(formatPtr)ARGUMENTS
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 han‐
dler to deal with files and strings in this format. The Tk_PhotoImage‐
Format structure contains the following fields:
typedef struct Tk_PhotoImageFormat {
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.
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,
char *fileName,
char *formatString,
int *widthPtr,
int *heightPtr);
The fileName argument is the name of the file containing the image
data, which is open for reading as chan. The formatString 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 suit‐
able for reading data from a given string. formatPtr->stringMatchProc
must match the following prototype:
typedef int Tk_ImageStringMatchProc(
char *string,
char *formatString,
int *widthPtr,
int *heightPtr);
The string argument points to the string containing the image data.
The formatString 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,
char *fileName,
char *formatString,
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 formatString 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 identi‐
fied 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 coordi‐
nates (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. for‐
matPtr->stringReadProc must match the following prototype:
typedef int Tk_ImageStringReadProc(
Tcl_Interp *interp,
char *string,
char *formatString,
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 string
argument points to the image data in string form. The formatString
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 proce‐
dure. 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,
char *fileName,
char *formatString,
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‐
String 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. for‐
matPtr->stringWriteProc must match the following prototype:
typedef int Tk_ImageStringWriteProc(
Tcl_Interp *interp,
Tcl_DString *dataPtr,
char *formatString,
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
appended to the dynamic string given by dataPtr. The formatString
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->stringWriteProc procedure may interpret these characters to
specify further details about the image file. The return value is a
standard Tcl return value.
SEE ALSO
Tk_FindPhoto, Tk_PhotoPutBlock
KEYWORDS
photo image, image file
Tk 4.0 Tk_CreatePhotoImageFormat(3)
