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 con-
verting image data to a string format. The user can spec-
ify which handler to use with the -format image configura-
tion 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 {
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
Tk_PhotoImageFormat structure should be set to NULL. The
handler must provide the fileMatchProc procedure if it
provides the fileReadProc procedure, and the stringMatch-
Proc procedure if it provides the stringReadProc proce-
dure.
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(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 proce-
dure 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 proto-
type:
typedef int Tk_ImageFileMatchProc(
FILE *f,
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 f. The for-
matString argument contains the value given for the -for-
mat 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 *width-
Ptr and *heightPtr respectively, and return 1. Otherwise
it should return 0.
STRINGMATCHPROC
formatPtr->stringMatchProc provides the address of a pro-
cedure 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(
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
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. Otherwise it should return 0.
FILEREADPROC
formatPtr->fileReadProc provides the address of a proce-
dure for Tk to call to read data from an image file into a
photo image. formatPtr->fileReadProc must match the fol-
lowing prototype:
typedef int Tk_ImageFileReadProc(
Tcl_Interp *interp,
FILE *f,
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 com-
mand 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 f. The format-
String 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 stan-
dard Tcl return value.
STRINGREADPROC
formatPtr->stringReadProc provides the address of a proce-
dure 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,
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 com-
mand was invoked to read the image; it should be used for
reporting errors. The string argument points to the image
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 pro-
cedure. The return value is a standard Tcl return value.
FILEWRITEPROC
formatPtr->fileWriteProc provides the address of a proce-
dure 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,
char *fileName,
char *formatString,
Tk_PhotoImageBlock *blockPtr);
The interp argument is the interpreter in which the com-
mand 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 struc-
ture pointed to by blockPtr; see the manual page Find-
Photo(3) for details. The fileName argument points to the
string giving the name of the file in which to write the
image data. 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 char-
acters 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 pro-
cedure 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_DString *dataPtr,
char *formatString,
Tk_PhotoImageBlock *blockPtr);
The interp argument is the interpreter in which the com-
mand 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
-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