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 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
transparent 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 previous contents showing
through in the transparent 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.
- 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 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(3tk)); 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 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 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 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_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 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 (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 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 subsequent 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.
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 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