tk_findphoto(3)

NAME

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

SYNOPSIS

#include <tk.h>
#include <tkPhoto.h>
Tk_PhotoHandle
Tk_FindPhoto(interp, imageName)
void
Tk_PhotoPutBlock(handle,  blockPtr,  x,  y, width, height,
compRule)
void
Tk_PhotoPutZoomedBlock(handle,  blockPtr,  x,  y,   width,
height,zoomX, zoomY, subsampleX, subsampleY, compRule)
int
Tk_PhotoGetImage(handle, blockPtr)
void
Tk_PhotoBlank(handle)
void
Tk_PhotoExpand(handle, width, height)
void
Tk_PhotoGetSize(handle, widthPtr, heightPtr)
void
Tk_PhotoSetSize(handle, width, height)

ARGUMENTS

Tcl_Interp *interp (in) Interpreter

in which
image was
created.

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 lay
out of image
data.

int x (in) Specifies the

X coordinate
where the
top-left cor
ner of the
block is to
be placed
within the
image.

int y (in) Specifies the

Y coordinate
where the
top-left cor
ner 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_Pho
toPutBlock) or the
desired image
width (for
Tk_PhotoEx pand and
Tk_PhotoSet Size).

int com_
pRule (in)

Specifies the
compositing
rule used
when combin
ing transpar
ent pixels in
a block of
data with a
photo image.
Must be one
of
TK_PHOTO_COM
POSITE_OVER
LAY (which
puts the
block of data
over the top
of the exist
ing photo
image, with
the previous
contents
showing
through in
the transpar
ent bits) or
TK_PHOTO_COM
POSITE_SET
(which dis
cards 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_Pho
toPutBlock) or the
desired image
height (for
Tk_PhotoEx pand 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 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.

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 cur
rent 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 pixel_
Size field specifies the address difference between two
horizontally adjacent pixels. Often it is 3 or 4, but it
can have any value. 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. 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_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 com
pletely 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 com
positing 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_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_PhotoPut ZoomedBlock 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 (possi
bly 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.
Tk_PhotoGetImage returns 1 for compatibility with the cor responding 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_PhotoSet Size at the beginning rather than allowing the image to
expand in many small increments as image blocks are sup
plied.

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

PORTABILITY

In Tk 8.3 and earlier, Tk_PhotoPutBlock and Tk_PhotoPut ZoomedBlock had different signatures. If you want to com pile code that uses the old interface against 8.4 without
updating your code, compile it with the flag -DUSE_COMPOS
ITELESS_PHOTO_PUT_BLOCK. 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)