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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
						    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.

       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.  Often it is 3 or  4,
       but  it can have any value.  The pitch field specifies the address dif‐
       ference between two vertically adjacent pixels.	The offset array  con‐
       tains  the  offsets from the address of a pixel to the addresses of the
       bytes containing the red, green, blue and alpha	(transparency)	compo‐
       nents.	These  are  normally 0, 1, 2 and 3, but can have other values,
       e.g., for images that are  stored  as  separate	red,  green  and  blue
       planes.

       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.  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.

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)
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