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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.

       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.  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  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.  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.

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 | CREDITS | KEYWORDS

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