Tk_PhotoBlank
Tk_FindPhoto(3) Tk Library Procedures Tk_FindPhoto(3)
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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>
#include <tkPhoto.h>
Tk_PhotoHandle
Tk_FindPhoto(interp, 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
Tcl_Interp *interp (in) Interpreter in which image |
was created.
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 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.
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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 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_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_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 8.0 Tk_FindPhoto(3)
