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FindPhoto(3)              Tk Library Procedures             FindPhoto(3)



______________________________________________________________________________


NAME

       Tk_FindPhoto,  Tk_PhotoPutBlock, Tk_PhotoPutZoomedBlock, Tk_PhotoGetIm-
       age, 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 exist-
                                                    ing  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_PhotoPut-
                                                    Block)  or   the   desired
                                                    image  height (for Tk_Pho-
                                                    toExpand and  Tk_PhotoSet-
                                                    Size).

       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 par-
       ticular 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 ima-
       geName  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  dis-
       played.   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 out-
       side 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(n));  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 dif-
       ference 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  cor-
       rectly  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 pro-
       vide  image  data  without  an  alpha channel by setting the offset for
       alpha to a negative value and adjusting  the  pixelSize  field  accord-
       ingly. 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_COM-
       POSITE_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  inde-
       pendently 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 sub-
       sampleY parameters allow the size of the image to be reduced by subsam-
       pling.   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 sub-
       sampleY 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 spe-
       cial 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_PhotoPut-
       ZoomedBlock.

       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_PhotoPutZoomed-
       Block 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_Pho-
       toPutBlock promises great flexibility in the layout of the  data  (e.g.
       separate planes for the red, green, blue and alpha channels).  Unfortu-
       nately, 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  pixel-
       Size  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



Tk                                    8.0                      FindPhoto(3)

tk 8.6.10 - Generated Sun Jan 5 13:23:51 CST 2020
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