Provided by: tk8.6-doc_8.6.8-4_all bug

NAME

       Tk_FindPhoto,  Tk_PhotoPutBlock,  Tk_PhotoPutZoomedBlock, Tk_PhotoGetImage, Tk_PhotoBlank,
       Tk_PhotoExpand, Tk_PhotoGetSize, Tk_PhotoSetSize - manipulate the image data stored  in  a
       photo image.

SYNOPSIS

       #include <tk.h>

       Tk_PhotoHandle
       Tk_FindPhoto(interp, imageName)

       int
       Tk_PhotoPutBlock(interp, handle, blockPtr, x, y, width, height,compRule)

       int
       Tk_PhotoPutZoomedBlock(interp, handle, blockPtr, x, y, width, height,zoomX, zoomY, subsampleX, subsampleY, compRule)

       int
       Tk_PhotoGetImage(handle, blockPtr)

       void
       Tk_PhotoBlank(handle)

       int
       Tk_PhotoExpand(interp, handle, width, height)

       void
       Tk_PhotoGetSize(handle, widthPtr, heightPtr)

       int
       Tk_PhotoSetSize(interp. handle, width, height)

ARGUMENTS

       Tcl_Interp *interp (in)                      Interpreter in which image was created and in
                                                    which error reporting is to be done.

       const char *imageName (in)                   Name of the photo image.

       Tk_PhotoHandle handle (in)                   Opaque handle identifying the photo image  to
                                                    be affected.

       Tk_PhotoImageBlock *blockPtr (in)            Specifies  the  address and storage layout of
                                                    image data.

       int x (in)                                   Specifies the X coordinate where the top-left
                                                    corner  of  the  block is to be placed within
                                                    the image.

       int y (in)                                   Specifies the Y coordinate where the top-left
                                                    corner  of  the  block is to be placed within
                                                    the image.

       int width (in)                               Specifies the width of the image area  to  be
                                                    affected   (for   Tk_PhotoPutBlock)   or  the
                                                    desired image width (for  Tk_PhotoExpand  and
                                                    Tk_PhotoSetSize).

       int compRule (in)                            Specifies  the  compositing  rule  used  when
                                                    combining transparent pixels in  a  block  of
                                                    data  with  a  photo  image.   Must be one of
                                                    TK_PHOTO_COMPOSITE_OVERLAY  (which  puts  the
                                                    block  of  data  over the top of the existing
                                                    photo  image,  with  the  previous   contents
                                                    showing  through  in the transparent bits) or
                                                    TK_PHOTO_COMPOSITE_SET  (which  discards  the
                                                    existing   photo   image   contents   in  the
                                                    rectangle covered by the data block.)

       int height (in)                              Specifies the height of the image area to  be
                                                    affected   (for   Tk_PhotoPutBlock)   or  the
                                                    desired image height (for Tk_PhotoExpand  and
                                                    Tk_PhotoSetSize).

       int *widthPtr (out)                          Pointer  to  location  in  which to store the
                                                    image width.

       int *heightPtr (out)                         Pointer to location in  which  to  store  the
                                                    image height.

       int subsampleX (in)                          Specifies  the  subsampling  factor  in the X
                                                    direction for input image data.

       int subsampleY (in)                          Specifies the subsampling  factor  in  the  Y
                                                    direction for input image data.

       int zoomX (in)                               Specifies  the  zoom  factor to be applied in
                                                    the X direction to pixels  being  written  to
                                                    the photo image.

       int zoomY (in)                               Specifies  the  zoom  factor to be applied in
                                                    the Y direction to pixels  being  written  to
                                                    the photo image.
_________________________________________________________________________________________________

DESCRIPTION

       Tk_FindPhoto returns an opaque handle that is used to identify a particular photo image to
       the other procedures.  The parameter is the name of the image, that is, the name specified
       to  the  image create photo command, or assigned by that command if no name was specified.
       If imageName does not exist or is not a photo image, Tk_FindPhoto returns NULL.

       Tk_PhotoPutBlock is used to supply blocks of image data to be displayed.  The call affects
       an  area  of  the  image  of  size  width  x  height  pixels,  with its top-left corner at
       coordinates (x,y).  All of width, height, x, and y must be non-negative.  If part of  this
       area  lies  outside the current bounds of the image, the image will be expanded to include
       the area, unless the user has specified an explicit image  size  with  the  -width  and/or
       -height  widget  configuration options (see photo(3tk)); in that case the area is silently
       clipped to the image boundaries.

       The block parameter is a pointer to a Tk_PhotoImageBlock structure, defined as follows:
              typedef struct {
                  unsigned char *pixelPtr;
                  int width;
                  int height;
                  int pitch;
                  int pixelSize;
                  int offset[4];
              } Tk_PhotoImageBlock;
       The pixelPtr field points to the first pixel, that is, the top-left pixel  in  the  block.
       The  width and height fields specify the dimensions of the block of pixels.  The pixelSize
       field specifies the address difference  between  two  horizontally  adjacent  pixels.   It
       should  be  4  for  RGB and 2 for grayscale image data.  Other values are possible, if the
       offsets in the offset array are adjusted accordingly (e.g. for red, green  and  blue  data
       stored  in different planes).  Using such a layout is strongly discouraged, though. Due to
       a bug, it might not work correctly if an alpha channel is provided. (see the BUGS  section
       below).  The  pitch field specifies the address difference between two vertically adjacent
       pixels.  The offset array contains the  offsets  from  the  address  of  a  pixel  to  the
       addresses  of  the  bytes  containing  the  red,  green,  blue  and  alpha  (transparency)
       components.  If the offsets for red, green and blue are equal, the image is interpreted as
       grayscale.  If  they  differ, RGB data is assumed. Normally the offsets will be 0, 1, 2, 3
       for RGB data and 0, 0, 0, 1 for grayscale.  It is possible to provide image  data  without
       an  alpha  channel  by  setting the offset for alpha to a negative value and adjusting the
       pixelSize field accordingly. This use is discouraged, though (see the BUGS section below).

       The compRule parameter to Tk_PhotoPutBlock specifies a compositing rule that says what  to
       do  with  transparent pixels.  The value TK_PHOTO_COMPOSITE_OVERLAY says that the previous
       contents of the photo image should show through, and the value TK_PHOTO_COMPOSITE_SET says
       that the previous contents of the photo image should be completely ignored, and the values
       from the block be  copied  directly  across.   The  behavior  in  Tk8.3  and  earlier  was
       equivalent to having TK_PHOTO_COMPOSITE_OVERLAY as a compositing rule.

       The  value  given  for  the width and height parameters to Tk_PhotoPutBlock do not have to
       correspond to the values specified  in  block.   If  they  are  smaller,  Tk_PhotoPutBlock
       extracts a sub-block from the image data supplied.  If they are larger, the data given are
       replicated (in a  tiled  fashion)  to  fill  the  specified  area.   These  rules  operate
       independently in the horizontal and vertical directions.

       Tk_PhotoPutBlock  normally  returns TCL_OK, though if it cannot allocate sufficient memory
       to hold the resulting image, TCL_ERROR is returned instead and, if the interp argument  is
       non-NULL, an error message is placed in the interpreter's result.

       Tk_PhotoPutZoomedBlock works like Tk_PhotoPutBlock except that the image can be reduced or
       enlarged for display.  The subsampleX and subsampleY parameters  allow  the  size  of  the
       image  to be reduced by subsampling.  Tk_PhotoPutZoomedBlock will use only pixels from the
       input image whose X coordinates are multiples of subsampleX, and whose Y  coordinates  are
       multiples  of  subsampleY.   For  example,  an  image  of 512x512 pixels can be reduced to
       256x256 by setting subsampleX and subsampleY to 2.

       The zoomX and zoomY parameters allow the image to be enlarged by pixel replication.   Each
       pixel  of  the  (possibly  subsampled) input image will be written to a block zoomX pixels
       wide and zoomY pixels high of the displayed image.  Subsampling and zooming  can  be  used
       together for special effects.

       Tk_PhotoGetImage  can be used to retrieve image data from a photo image.  Tk_PhotoGetImage
       fills in the structure pointed to by the blockPtr parameter with values that describe  the
       address  and  layout  of  the  image data that the photo image has stored internally.  The
       values are valid until the image is destroyed or its size is changed.

       It is possible to modify an image by writing directly  to  the  data  the  pixelPtr  field
       points  to.  The size of the image cannot be changed this way, though.  Also, changes made
       by writing directly to pixelPtr will not be immediately visible, but only after a call  to
       Tk_ImageChanged or after an event that causes the interested widgets to redraw themselves.
       For these reasons usually it is preferable to make changes to a copy of the image data and
       write it back with Tk_PhotoPutBlock or Tk_PhotoPutZoomedBlock.

       Tk_PhotoGetImage  returns  1 for compatibility with the corresponding procedure in the old
       photo widget.

       Tk_PhotoBlank blanks the entire area of the photo image.  Blank areas of a photo image are
       transparent.

       Tk_PhotoExpand  requests that the widget's image be expanded to be at least width x height
       pixels in size.  The width and/or height are  unchanged  if  the  user  has  specified  an
       explicit  image  width  or  height  with  the -width and/or -height configuration options,
       respectively.  If the image data are being supplied in  many  small  blocks,  it  is  more
       efficient  to  use Tk_PhotoExpand or Tk_PhotoSetSize at the beginning rather than allowing
       the image to expand in many small increments as image blocks are supplied.

       Tk_PhotoExpand normally returns TCL_OK, though if it cannot allocate sufficient memory  to
       hold  the  resulting  image,  TCL_ERROR is returned instead and, if the interp argument is
       non-NULL, an error message is placed in the interpreter's result.

       Tk_PhotoSetSize specifies the size of the image, as if the user had  specified  the  given
       width  and height values to the -width and -height configuration options.  A value of zero
       for width or height does not change the image's width or height, but allows the  width  or
       height  to  be  changed by subsequent calls to Tk_PhotoPutBlock, Tk_PhotoPutZoomedBlock or
       Tk_PhotoExpand.

       Tk_PhotoSetSize normally returns TCL_OK, though if it cannot allocate sufficient memory to
       hold  the  resulting  image,  TCL_ERROR is returned instead and, if the interp argument is
       non-NULL, an error message is placed in the interpreter's result.

       Tk_PhotoGetSize returns the dimensions of the image in *widthPtr and *heightPtr.

PORTABILITY

       In  Tk  8.3  and  earlier,  Tk_PhotoPutBlock  and  Tk_PhotoPutZoomedBlock  had   different
       signatures.  If  you  want to compile code that uses the old interface against 8.4 without
       updating your code, compile it with the  flag  -DUSE_COMPOSITELESS_PHOTO_PUT_BLOCK.   Code
       linked using Stubs against older versions of Tk will continue to work.

       In  Tk  8.4,  Tk_PhotoPutBlock, Tk_PhotoPutZoomedBlock, Tk_PhotoExpand and Tk_PhotoSetSize
       did not take an interp argument or return any result code.   If  insufficient  memory  was
       available  for an image, Tk would panic.  This behaviour is still supported if you compile
       your extension with the additional flag -DUSE_PANIC_ON_PHOTO_ALLOC_FAILURE.   Code  linked
       using Stubs against older versions of Tk will continue to work.

BUGS

       The  Tk_PhotoImageBlock  structure used to provide image data to Tk_PhotoPutBlock promises
       great flexibility in the layout of the data (e.g. separate planes for the red, green, blue
       and  alpha  channels).  Unfortunately, the implementation fails to hold this promise.  The
       problem is that the pixelSize field is (incorrectly) used to determine whether  the  image
       has  an alpha channel.  Currently, if the offset for the alpha channel is greater or equal
       than pixelSize, tk_PhotoPutblock assumes no alpha data is  present  and  makes  the  image
       fully  opaque.   This means that for layouts where the channels are separate (or any other
       exotic layout where pixelSize has to be smaller than the alpha offset), the alpha  channel
       will  not  be  read  correctly.   In  order  to  be on the safe side if this issue will be
       corrected in a future release, it is strongly recommended you always provide alpha data  -
       even  if  the  image  has  no  transparency  -  and  only use the "standard" layout with a
       pixelSize of 2 for grayscale and 4 for RGB data with offsets of 0, 0, 0, 1 or 0, 1,  2,  3
       respectively.

CREDITS

       The  code  for  the photo image type was developed by Paul Mackerras, based on his earlier
       photo widget code.

KEYWORDS

       photo, image