FreeBSD Manual Pages

home | help

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 - manipu-
late 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 re-
porting 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 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 im-
age area to be affected (for
Tk_PhotoPutBlock) or the de-
sired image width (for Tk_Pho-
toExpand and Tk_PhotoSetSize).

int compRule (in) Specifies the compositing rule
used when combining transpar-
ent pixels in a block of data
with a photo image. Must be
one of TK_PHOTO_COMPOS-
ITE_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_COMPOS-
ITE_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 de-
sired image height (for
Tk_PhotoExpand and Tk_Photo-
SetSize).

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 fac-
tor in the X direction for in-
put image data.

int subsampleY (in) Specifies the subsampling fac-
tor in the Y direction for in-
put 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 im-
age, that is, the name specified to the image create photo command, or as-
signed by that command if no name was specified. If imageName does not ex-
ist or is not a photo image, Tk_FindPhoto returns NULL.

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 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 difference be-
tween two horizontally adjacent pixels. It should be 4 for RGB and 2 for
grayscale image data. Other values are possible, if the offsets in the
offset array are adjusted accordingly (e.g. for red, green and blue data
stored in different planes). Using such a layout is strongly discouraged,
though. Due to a bug, it might not work correctly if an alpha channel is
provided. (see the BUGS section below). The pitch field specifies the ad-
dress 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.
If the offsets for red, green and blue are equal, the image is interpreted
as grayscale. If they differ, RGB data is assumed. Normally the offsets
will be 0, 1, 2, 3 for RGB data and 0, 0, 0, 1 for grayscale. It is possi-
ble to provide image data without an alpha channel by setting the offset
for alpha to a negative value and adjusting the pixelSize field accord-
ingly. This use is discouraged, though (see the BUGS section below).

The compRule parameter to Tk_PhotoPutBlock specifies a compositing rule
that says what to do with transparent pixels. The value TK_PHOTO_COMPOS-
ITE_OVERLAY says that the previous contents of the photo image should show
through, and the value TK_PHOTO_COMPOSITE_SET says that the previous con-
tents 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 sup-
plied. If they are larger, the data given are replicated (in a tiled fash-
ion) to fill the specified area. These rules operate independently in the
horizontal and vertical directions.

Tk_PhotoPutBlock normally returns TCL_OK, though if it cannot allocate suf-
ficient 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 pa-
rameters allow the size of the image to be reduced by subsampling. Tk_Pho-
toPutZoomedBlock 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 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 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 parame-
ter 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 im-
age is destroyed or its size is changed.

It is possible to modify an image by writing directly to the data the pix-
elPtr field points to. The size of the image cannot be changed this way,
though. Also, changes made by writing directly to pixelPtr will not be im-
mediately visible, but only after a call to Tk_ImageChanged or after an
event that causes the interested widgets to redraw themselves. For these
reasons usually it is preferable to make changes to a copy of the image
data and write it back with Tk_PhotoPutBlock or Tk_PhotoPutZoomedBlock.

Tk_PhotoGetImage returns 1 for compatibility with the corresponding proce-
dure 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_Photo-
Expand 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 suffi-
cient 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 speci-
fied the given width and height values to the -width and -height configura-
tion options. A value of zero for width or height does not change the im-
age's width or height, but allows the width or height to be changed by sub-
sequent calls to Tk_PhotoPutBlock, Tk_PhotoPutZoomedBlock or Tk_PhotoEx-
pand.

Tk_PhotoSetSize normally returns TCL_OK, though if it cannot allocate suf-
ficient 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 dif-
ferent 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_COM-
POSITELESS_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 addi-
tional flag -DUSE_PANIC_ON_PHOTO_ALLOC_FAILURE. Code linked using Stubs
against older versions of Tk will continue to work.

BUGS
The Tk_PhotoImageBlock structure used to provide image data to Tk_PhotoPut-
Block promises great flexibility in the layout of the data (e.g. separate
planes for the red, green, blue and alpha channels). Unfortunately, the
implementation fails to hold this promise. The problem is that the pixel-
Size field is (incorrectly) used to determine whether the image has an al-
pha channel. Currently, if the offset for the alpha channel is greater
than or equal to pixelSize, tk_PhotoPutblock assumes no alpha data is
present and makes the image fully opaque. This means that for layouts
where the channels are separate (or any other exotic layout where pixelSize
has to be smaller than the alpha offset), the alpha channel will not be
read correctly. In order to be on the safe side if this issue will be cor-
rected in a future release, it is strongly recommended you always provide
alpha data - even if the image has no transparency - and only use the
"standard" layout with a pixelSize of 2 for grayscale and 4 for RGB data
with offsets of 0, 0, 0, 1 or 0, 1, 2, 3 respectively.

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)

Want to link to this manual page? Use this URL:
<https://man.freebsd.org/cgi/man.cgi?query=Tk_PhotoGetSize.tk86&sektion=3&manpath=FreeBSD+Ports+15.1.quarterly>

home | help

Header And Logo

Peripheral Links

Site Navigation

FreeBSD Manual Pages

Header And Logo

Peripheral Links

Search

Site Navigation

FreeBSD Manual Pages