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Tk_FindPhoto(3)		     Tk	Library	Procedures	       Tk_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 af-
						    fected.

       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  af-
						    fected  (for  Tk_PhotoPut-
						    Block) or the desired  im-
						    age	 height	(for Tk_Photo-
						    Expand  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 di-
						    rection  to	 pixels	 being
						    written to the  photo  im-
						    age.

       int zoomY (in)				    Specifies  the zoom	factor
						    to be applied in the Y di-
						    rection  to	 pixels	 being
						    written to the  photo  im-
						    age.
______________________________________________________________________________

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 in-
       clude  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, de-
       fined 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 ad-
       dress 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 al-
       pha 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_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  im-
       age can be reduced or enlarged for display.  The	subsampleX and subsam-
       pleY parameters allow the size of the image to be  reduced  by  subsam-
       pling.	Tk_PhotoPutZoomedBlock will use	only pixels from the input im-
       age whose X coordinates are multiples of	subsampleX, and	whose Y	 coor-
       dinates	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 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  pa-
       rameter	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 un-
       changed 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  ef-
       ficient	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 in-
       terface	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		       Tk_FindPhoto(3)

NAME | SYNOPSIS | ARGUMENTS | DESCRIPTION | PORTABILITY | BUGS | CREDITS | KEYWORDS

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