Tk_FindPhoto(3)
Tk_FindPhoto(3) Tk Library Procedures Tk_FindPhoto(3)
_________________________________________________________________
NAME
Tk_FindPhoto, Tk_PhotoPutBlock, Tk_PhotoPutZoomedBlock,
Tk_PhotoGetImage, 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
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Tk_FindPhoto(3) Tk Library Procedures Tk_FindPhoto(3)
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 tran-
sparent 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 previ-
ous contents
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Tk_FindPhoto(3) Tk Library Procedures Tk_FindPhoto(3)
showing through
in the tran-
sparent bits)
or
TK_PHOTO_COMPOSITE_SET
(which discards
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_PhotoPutBlock)
or the desired
image height
(for
Tk_PhotoExpand
and
Tk_PhotoSetSize).
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.
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Tk_FindPhoto(3) Tk Library Procedures Tk_FindPhoto(3)
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 iden-
tify a particular photo image to the other procedures. The
parameter is the name of the image, that is, the name speci-
fied 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 coordi-
nates (x,y). All of width, height, x, and y must be non-
negative. If part of this area lies outside 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 pixel-
Size field specifies the address difference between two hor-
izontally adjacent pixels. Often it is 3 or 4, but it can
have any value. The pitch field specifies the address
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Tk_FindPhoto(3) Tk Library Procedures Tk_FindPhoto(3)
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 com-
positing 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 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
independently in the horizontal and vertical directions.
Tk_PhotoPutBlock normally returns TCL_OK, though if it can- |
not 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 subsampleY parameters allow the size of the
image to be reduced by subsampling. Tk_PhotoPutZoomedBlock
will use only pixels from the input image whose X coordi-
nates 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 subsam-
pleX 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 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
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Tk_FindPhoto(3) Tk Library Procedures Tk_FindPhoto(3)
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 sub-
sequent calls to Tk_PhotoPutBlock, Tk_PhotoPutZoomedBlock 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.
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Tk_FindPhoto(3) Tk Library Procedures Tk_FindPhoto(3)
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 con- |
tinue 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
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