284 lines
13 KiB
Groff
284 lines
13 KiB
Groff
'\"
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'\" Copyright (c) 1994 The Australian National University
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'\" Copyright (c) 1994-1996 Sun Microsystems, Inc.
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'\"
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'\" See the file "license.terms" for information on usage and redistribution
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'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
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'\"
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'\" Author: Paul Mackerras (paulus@cs.anu.edu.au),
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'\" Department of Computer Science,
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'\" Australian National University.
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'\"
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.TH Tk_FindPhoto 3 8.0 Tk "Tk Library Procedures"
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.so man.macros
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.BS
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.SH NAME
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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.
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.SH SYNOPSIS
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.nf
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\fB#include <tk.h>\fR
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.sp
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Tk_PhotoHandle
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\fBTk_FindPhoto\fR(\fIinterp, imageName\fR)
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.sp
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int
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\fBTk_PhotoPutBlock\fR(\fIinterp, handle, blockPtr, x, y, width, height,\
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compRule\fR)
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.sp
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int
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\fBTk_PhotoPutZoomedBlock\fR(\fIinterp, handle, blockPtr, x, y, width, height,\
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zoomX, zoomY, subsampleX, subsampleY, compRule\fR)
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.sp
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int
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\fBTk_PhotoGetImage\fR(\fIhandle, blockPtr\fR)
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.sp
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void
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\fBTk_PhotoBlank\fR(\fIhandle\fR)
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.sp
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int
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\fBTk_PhotoExpand\fR(\fIinterp, handle, width, height\fR)
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.sp
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void
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\fBTk_PhotoGetSize\fR(\fIhandle, widthPtr, heightPtr\fR)
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.sp
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int
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\fBTk_PhotoSetSize\fR(\fIinterp. handle, width, height\fR)
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.SH ARGUMENTS
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.AS Tk_PhotoImageBlock window_path
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.AP Tcl_Interp *interp in
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Interpreter in which image was created and in which error reporting is
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to be done.
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.AP "const char" *imageName in
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Name of the photo image.
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.AP Tk_PhotoHandle handle in
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Opaque handle identifying the photo image to be affected.
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.AP Tk_PhotoImageBlock *blockPtr in
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Specifies the address and storage layout of image data.
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.AP int x in
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Specifies the X coordinate where the top-left corner of the block is
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to be placed within the image.
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.AP int y in
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Specifies the Y coordinate where the top-left corner of the block is
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to be placed within the image.
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.AP int width in
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Specifies the width of the image area to be affected (for
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\fBTk_PhotoPutBlock\fR) or the desired image width (for
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\fBTk_PhotoExpand\fR and \fBTk_PhotoSetSize\fR).
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.AP int compRule in
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Specifies the compositing rule used when combining transparent pixels
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in a block of data with a photo image. Must be one of
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\fBTK_PHOTO_COMPOSITE_OVERLAY\fR (which puts the block of data over the top
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of the existing photo image, with the previous contents showing
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through in the transparent bits) or \fBTK_PHOTO_COMPOSITE_SET\fR (which
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discards the existing photo image contents in the rectangle covered by
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the data block.)
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.AP int height in
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Specifies the height of the image area to be affected (for
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\fBTk_PhotoPutBlock\fR) or the desired image height (for
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\fBTk_PhotoExpand\fR and \fBTk_PhotoSetSize\fR).
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.AP int *widthPtr out
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Pointer to location in which to store the image width.
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.AP int *heightPtr out
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Pointer to location in which to store the image height.
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.AP int subsampleX in
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Specifies the subsampling factor in the X direction for input
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image data.
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.AP int subsampleY in
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Specifies the subsampling factor in the Y direction for input
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image data.
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.AP int zoomX in
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Specifies the zoom factor to be applied in the X direction to pixels
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being written to the photo image.
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.AP int zoomY in
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Specifies the zoom factor to be applied in the Y direction to pixels
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being written to the photo image.
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.BE
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.SH DESCRIPTION
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.PP
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\fBTk_FindPhoto\fR returns an opaque handle that is used to identify a
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particular photo image to the other procedures. The parameter is the
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name of the image, that is, the name specified to the \fBimage create
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photo\fR command, or assigned by that command if no name was specified.
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If \fIimageName\fR does not exist or is not a photo image,
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\fBTk_FindPhoto\fR returns NULL.
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.PP
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\fBTk_PhotoPutBlock\fR is used to supply blocks of image data to be
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displayed. The call affects an area of the image of size
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\fIwidth\fR x \fIheight\fR pixels, with its top-left corner at
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coordinates (\fIx\fR,\fIy\fR). All of \fIwidth\fR, \fIheight\fR,
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\fIx\fR, and \fIy\fR must be non-negative.
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If part of this area lies outside the
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current bounds of the image, the image will be expanded to include the
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area, unless the user has specified an explicit image size with the
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\fB\-width\fR and/or \fB\-height\fR widget configuration options
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(see photo(n)); in that
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case the area is silently clipped to the image boundaries.
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.PP
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The \fIblock\fR parameter is a pointer to a
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\fBTk_PhotoImageBlock\fR structure, defined as follows:
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.CS
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typedef struct {
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unsigned char *\fIpixelPtr\fR;
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int \fIwidth\fR;
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int \fIheight\fR;
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int \fIpitch\fR;
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int \fIpixelSize\fR;
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int \fIoffset\fR[4];
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} \fBTk_PhotoImageBlock\fR;
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.CE
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The \fIpixelPtr\fR field points to the first pixel, that is, the
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top-left pixel in the block.
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The \fIwidth\fR and \fIheight\fR fields specify the dimensions of the
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block of pixels. The \fIpixelSize\fR field specifies the address
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difference between two horizontally adjacent pixels. It should be 4 for
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RGB and 2 for grayscale image data. Other values are possible, if the
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offsets in the \fIoffset\fR array are adjusted accordingly (e.g. for
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red, green and blue data stored in different planes). Using such a
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layout is strongly discouraged, though. Due to a bug, it might not work
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correctly if an alpha channel is provided. (see the \fBBUGS\fR section
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below). The \fIpitch\fR field specifies the
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address difference between two vertically adjacent pixels. The
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\fIoffset\fR array contains the offsets from the address of a pixel
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to the addresses of the bytes containing the red, green, blue and alpha
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(transparency) components. If the offsets for red, green and blue are
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equal, the image is interpreted as grayscale. If they differ, RGB data
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is assumed. Normally the offsets will be 0, 1, 2, 3 for RGB data
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and 0, 0, 0, 1 for grayscale. It is possible to provide image data
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without an alpha channel by setting the offset for alpha to a negative
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value and adjusting the \fIpixelSize\fR field accordingly. This use is
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discouraged, though (see the \fBBUGS\fR section below).
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.PP
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The \fIcompRule\fR parameter to \fBTk_PhotoPutBlock\fR specifies a
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compositing rule that says what to do with transparent pixels. The
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value \fBTK_PHOTO_COMPOSITE_OVERLAY\fR says that the previous contents of
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the photo image should show through, and the value
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\fBTK_PHOTO_COMPOSITE_SET\fR says that the previous contents of the photo
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image should be completely ignored, and the values from the block be
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copied directly across. The behavior in Tk8.3 and earlier was
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equivalent to having \fBTK_PHOTO_COMPOSITE_OVERLAY\fR as a compositing rule.
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.PP
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The value given for the \fIwidth\fR and \fIheight\fR parameters to
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\fBTk_PhotoPutBlock\fR do not have to correspond to the values specified
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in \fIblock\fR. If they are smaller, \fBTk_PhotoPutBlock\fR extracts a
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sub-block from the image data supplied. If they are larger, the data
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given are replicated (in a tiled fashion) to fill the specified area.
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These rules operate independently in the horizontal and vertical
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directions.
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.PP
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\fBTk_PhotoPutBlock\fR normally returns \fBTCL_OK\fR, though if it cannot
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allocate sufficient memory to hold the resulting image, \fBTCL_ERROR\fR is
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returned instead and, if the \fIinterp\fR argument is non-NULL, an
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error message is placed in the interpreter's result.
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.PP
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\fBTk_PhotoPutZoomedBlock\fR works like \fBTk_PhotoPutBlock\fR except that
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the image can be reduced or enlarged for display. The
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\fIsubsampleX\fR and \fIsubsampleY\fR parameters allow the size of the
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image to be reduced by subsampling.
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\fBTk_PhotoPutZoomedBlock\fR will use only pixels from the input image
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whose X coordinates are multiples of \fIsubsampleX\fR, and whose Y
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coordinates are multiples of \fIsubsampleY\fR. For example, an image
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of 512x512 pixels can be reduced to 256x256 by setting
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\fIsubsampleX\fR and \fIsubsampleY\fR to 2.
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.PP
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The \fIzoomX\fR and \fIzoomY\fR parameters allow the image to be
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enlarged by pixel replication. Each pixel of the (possibly subsampled)
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input image will be written to a block \fIzoomX\fR pixels wide and
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\fIzoomY\fR pixels high of the displayed image. Subsampling and
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zooming can be used together for special effects.
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.PP
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\fBTk_PhotoGetImage\fR can be used to retrieve image data from a photo
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image. \fBTk_PhotoGetImage\fR fills
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in the structure pointed to by the \fIblockPtr\fR parameter with values
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that describe the address and layout of the image data that the
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photo image has stored internally. The values are valid
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until the image is destroyed or its size is changed.
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.PP
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It is possible to modify an image by writing directly to the data
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the \fIpixelPtr\fR field points to. The size of the image cannot be
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changed this way, though.
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Also, changes made by writing directly to \fIpixelPtr\fR will not be
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immediately visible, but only after a call to
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\fBTk_ImageChanged\fR or after an event that causes the interested
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widgets to redraw themselves.
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For these reasons usually it is preferable to make changes to
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a copy of the image data and write it back with
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\fBTk_PhotoPutBlock\fR or \fBTk_PhotoPutZoomedBlock\fR.
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.PP
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\fBTk_PhotoGetImage\fR returns 1 for compatibility with the
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corresponding procedure in the old photo widget.
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.PP
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\fBTk_PhotoBlank\fR blanks the entire area of the
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photo image. Blank areas of a photo image are transparent.
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.PP
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\fBTk_PhotoExpand\fR requests that the widget's image be expanded to be
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at least \fIwidth\fR x \fIheight\fR pixels in size. The width and/or
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height are unchanged if the user has specified an explicit image width
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or height with the \fB\-width\fR and/or \fB\-height\fR configuration
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options, respectively.
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If the image data
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are being supplied in many small blocks, it is more efficient to use
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\fBTk_PhotoExpand\fR or \fBTk_PhotoSetSize\fR at the beginning rather than
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allowing the image to expand in many small increments as image blocks
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are supplied.
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.PP
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\fBTk_PhotoExpand\fR normally returns \fBTCL_OK\fR, though if it cannot
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allocate sufficient memory to hold the resulting image, \fBTCL_ERROR\fR is
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returned instead and, if the \fIinterp\fR argument is non-NULL, an
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error message is placed in the interpreter's result.
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.PP
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\fBTk_PhotoSetSize\fR specifies the size of the image, as if the user
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had specified the given \fIwidth\fR and \fIheight\fR values to the
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\fB\-width\fR and \fB\-height\fR configuration options. A value of
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zero for \fIwidth\fR or \fIheight\fR does not change the image's width
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or height, but allows the width or height to be changed by subsequent
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calls to \fBTk_PhotoPutBlock\fR, \fBTk_PhotoPutZoomedBlock\fR or
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\fBTk_PhotoExpand\fR.
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.PP
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\fBTk_PhotoSetSize\fR normally returns \fBTCL_OK\fR, though if it cannot
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allocate sufficient memory to hold the resulting image, \fBTCL_ERROR\fR is
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returned instead and, if the \fIinterp\fR argument is non-NULL, an
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error message is placed in the interpreter's result.
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.PP
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\fBTk_PhotoGetSize\fR returns the dimensions of the image in
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*\fIwidthPtr\fR and *\fIheightPtr\fR.
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.SH PORTABILITY
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.PP
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In Tk 8.3 and earlier, \fBTk_PhotoPutBlock\fR and
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\fBTk_PhotoPutZoomedBlock\fR had different signatures. If you want to
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compile code that uses the old interface against 8.4 without updating
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your code, compile it with the flag
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-DUSE_COMPOSITELESS_PHOTO_PUT_BLOCK. Code linked using Stubs against
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older versions of Tk will continue to work.
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.PP
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In Tk 8.4, \fBTk_PhotoPutBlock\fR, \fBTk_PhotoPutZoomedBlock\fR,
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\fBTk_PhotoExpand\fR and \fBTk_PhotoSetSize\fR did not take an
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\fIinterp\fR argument or return any result code. If insufficient
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memory was available for an image, Tk would panic. This behaviour is
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still supported if you compile your extension with the additional flag
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-DUSE_PANIC_ON_PHOTO_ALLOC_FAILURE. Code linked using Stubs against
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older versions of Tk will continue to work.
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.SH BUGS
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The \fBTk_PhotoImageBlock\fR structure used to provide image data to
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\fBTk_PhotoPutBlock\fR promises great flexibility in the layout of the
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data (e.g. separate planes for the red, green, blue and alpha
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channels). Unfortunately, the implementation fails to hold this
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promise. The problem is that the \fIpixelSize\fR field is
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(incorrectly) used to determine whether the image has an alpha channel.
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Currently, if the offset for the alpha channel is greater or equal than
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\fIpixelSize\fR, \fBtk_PhotoPutblock\fR assumes no alpha data is
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present and makes the image fully opaque. This means that for layouts
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where the channels are separate (or any other exotic layout where
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\fIpixelSize\fR has to be smaller than the alpha offset), the alpha
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channel will not be read correctly. In order to be on the safe side
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if this issue will be corrected in a future release, it is strongly
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recommended you always provide alpha data - even if the image has no
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transparency - and only use the "standard" layout with a
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\fIpixelSize\fR of 2 for grayscale and 4 for RGB data with
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\fIoffset\fRs of 0, 0, 0, 1 or 0, 1, 2, 3 respectively.
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.SH CREDITS
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.PP
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The code for the photo image type was developed by Paul Mackerras,
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based on his earlier photo widget code.
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.SH KEYWORDS
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photo, image
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