Tk_FindPhoto(3) Tk Library Procedures 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(imageName)
void
Tk_PhotoPutBlock(handle, blockPtr, x, y, width, height)
void
Tk_PhotoPutZoomedBlock(handle, blockPtr, x, y, width, height,zoomX, zoomY, subsampleX, subsampleY)
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
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
Tk 4.0 1
Tk_FindPhoto(3) Tk Library Procedures Tk_FindPhoto(3)
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 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
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Tk_FindPhoto(3) Tk Library Procedures Tk_FindPhoto(3)
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
Tk 4.0 3
Tk_FindPhoto(3) Tk Library Procedures Tk_FindPhoto(3)
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[3];
} 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 and blue components. These are normally 0, 1 and 2,
but can have other values, e.g., for images that are
stored as separate red, green and blue planes.
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
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Tk_FindPhoto(3) Tk Library Procedures Tk_FindPhoto(3)
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.
CREDITS
The code for the photo image type was developed by Paul
Mackerras, based on his earlier photo widget code.
KEYWORDS
photo, image
Tk 4.0 5
