tk4.2 C API - CrtPhImgFmt






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 sup-
     port 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 con-
     tains 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 pro-
     cedures.   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 pro-
     cedure, 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(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(
            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 format-
     String 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  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
     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,
            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  command
     was invoked to read the image; it should be used for report-
     ing errors.  The image data is in the file  named  fileName,
     which  is  open for reading as f.  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
     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  coor-
     dinates  (destX,destY) using the Tk_PhotoPutBlock procedure.
     The return value is a standard Tcl return value.



STRINGREADPROC

     formatPtr->stringReadProc provides the  address  of  a  pro-
     cedure  for  Tk  to  call  to read data from a string into a
     photo image.  formatPtr->stringReadProc must match the  fol-
     lowing 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 report-
     ing 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 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,
            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_PhotoImageBlock structure
     pointed to by blockPtr; see the manual page FindPhoto(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 -for-
     mat 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  stan-
     dard 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  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 appropri-
     ate, 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.



SEE ALSO

     Tk_FindPhoto, Tk_PhotoPutBlock



KEYWORDS

     photo image, image file