1Tk_FindPhoto(3) Tk Library Procedures Tk_FindPhoto(3)
2______________________________________________________________________________
6
8 Tk_FindPhoto, Tk_PhotoPutBlock, Tk_PhotoPutZoomedBlock, Tk_PhotoGetIm‐
9 age, Tk_PhotoBlank, Tk_PhotoExpand, Tk_PhotoGetSize, Tk_PhotoSetSize -
10 manipulate the image data stored in a photo image.
11
13 #include <tk.h>
14 Tk_PhotoHandle
16 Tk_FindPhoto(interp, imageName)
17 int
19 Tk_PhotoPutBlock(interp, handle, blockPtr, x, y, width, height,compRule)
20 int
22 Tk_PhotoPutZoomedBlock(interp, handle, blockPtr, x, y, width, height,zoomX, zoomY, subsampleX, subsampleY, compRule)
23 int
25 Tk_PhotoGetImage(handle, blockPtr)
26 void
28 Tk_PhotoBlank(handle)
29 int
31 Tk_PhotoExpand(interp, handle, width, height)
32 void
34 Tk_PhotoGetSize(handle, widthPtr, heightPtr)
35 int
37 Tk_PhotoSetSize(interp. handle, width, height)
38
40 Tcl_Interp *interp (in) Interpreter in which image
41 was created and in which
42 error reporting is to be
43 done.
44 const char *imageName (in) Name of the photo image.
46 Tk_PhotoHandle handle (in) Opaque handle identifying
48 the photo image to be
49 affected.
50 Tk_PhotoImageBlock *blockPtr (in) Specifies the address and
52 storage layout of image
53 data.
54 int x (in) Specifies the X coordinate
56 where the top-left corner
57 of the block is to be
58 placed within the image.
59 int y (in) Specifies the Y coordinate
61 where the top-left corner
62 of the block is to be
63 placed within the image.
64 int width (in) Specifies the width of the
66 image area to be affected
67 (for Tk_PhotoPutBlock) or
68 the desired image width
69 (for Tk_PhotoExpand and
70 Tk_PhotoSetSize).
71 int compRule (in) Specifies the compositing
73 rule used when combining
74 transparent pixels in a
75 block of data with a photo
76 image. Must be one of
77 TK_PHOTO_COMPOSITE_OVERLAY
78 (which puts the block of
79 data over the top of the
80 existing photo image, with
81 the previous contents
82 showing through in the
83 transparent bits) or
84 TK_PHOTO_COMPOSITE_SET
85 (which discards the exist‐
86 ing photo image contents
87 in the rectangle covered
88 by the data block.)
89 int height (in) Specifies the height of
91 the image area to be
92 affected (for Tk_PhotoPut‐
93 Block) or the desired
94 image height (for Tk_Pho‐
95 toExpand and Tk_PhotoSet‐
96 Size).
97 int *widthPtr (out) Pointer to location in
99 which to store the image
100 width.
101 int *heightPtr (out) Pointer to location in
103 which to store the image
104 height.
105 int subsampleX (in) Specifies the subsampling
107 factor in the X direction
108 for input image data.
109 int subsampleY (in) Specifies the subsampling
111 factor in the Y direction
112 for input image data.
113 int zoomX (in) Specifies the zoom factor
115 to be applied in the X
116 direction to pixels being
117 written to the photo
118 image.
119 int zoomY (in) Specifies the zoom factor
121 to be applied in the Y
122 direction to pixels being
123 written to the photo
124 image.
125______________________________________________________________________________
126
128 Tk_FindPhoto returns an opaque handle that is used to identify a par‐
129 ticular photo image to the other procedures. The parameter is the name
130 of the image, that is, the name specified to the image create photo
131 command, or assigned by that command if no name was specified. If ima‐
132 geName does not exist or is not a photo image, Tk_FindPhoto returns
133 NULL.
134 Tk_PhotoPutBlock is used to supply blocks of image data to be dis‐
136 played. The call affects an area of the image of size width x height
137 pixels, with its top-left corner at coordinates (x,y). All of width,
138 height, x, and y must be non-negative. If part of this area lies out‐
139 side the current bounds of the image, the image will be expanded to
140 include the area, unless the user has specified an explicit image size
141 with the -width and/or -height widget configuration options (see
142 photo(n)); in that case the area is silently clipped to the image
143 boundaries.
144 The block parameter is a pointer to a Tk_PhotoImageBlock structure,
146 defined as follows:
147 typedef struct {
148 unsigned char *pixelPtr;
149 int width;
150 int height;
151 int pitch;
152 int pixelSize;
153 int offset[4];
154 } Tk_PhotoImageBlock;
155 The pixelPtr field points to the first pixel, that is, the top-left
156 pixel in the block. The width and height fields specify the dimensions
157 of the block of pixels. The pixelSize field specifies the address dif‐
158 ference between two horizontally adjacent pixels. It should be 4 for
159 RGB and 2 for grayscale image data. Other values are possible, if the
160 offsets in the offset array are adjusted accordingly (e.g. for red,
161 green and blue data stored in different planes). Using such a layout
162 is strongly discouraged, though. Due to a bug, it might not work cor‐
163 rectly if an alpha channel is provided. (see the BUGS section below).
164 The pitch field specifies the address difference between two vertically
165 adjacent pixels. The offset array contains the offsets from the
166 address of a pixel to the addresses of the bytes containing the red,
167 green, blue and alpha (transparency) components. If the offsets for
168 red, green and blue are equal, the image is interpreted as grayscale.
169 If they differ, RGB data is assumed. Normally the offsets will be 0, 1,
170 2, 3 for RGB data and 0, 0, 0, 1 for grayscale. It is possible to pro‐
171 vide image data without an alpha channel by setting the offset for
172 alpha to a negative value and adjusting the pixelSize field accord‐
173 ingly. This use is discouraged, though (see the BUGS section below).
174 The compRule parameter to Tk_PhotoPutBlock specifies a compositing rule
176 that says what to do with transparent pixels. The value TK_PHOTO_COM‐
177 POSITE_OVERLAY says that the previous contents of the photo image
178 should show through, and the value TK_PHOTO_COMPOSITE_SET says that the
179 previous contents of the photo image should be completely ignored, and
180 the values from the block be copied directly across. The behavior in
181 Tk8.3 and earlier was equivalent to having TK_PHOTO_COMPOSITE_OVERLAY
182 as a compositing rule.
183 The value given for the width and height parameters to Tk_PhotoPutBlock
185 do not have to correspond to the values specified in block. If they
186 are smaller, Tk_PhotoPutBlock extracts a sub-block from the image data
187 supplied. If they are larger, the data given are replicated (in a
188 tiled fashion) to fill the specified area. These rules operate inde‐
189 pendently in the horizontal and vertical directions.
190 Tk_PhotoPutBlock normally returns TCL_OK, though if it cannot allocate
192 sufficient memory to hold the resulting image, TCL_ERROR is returned
193 instead and, if the interp argument is non-NULL, an error message is
194 placed in the interpreter's result.
195 Tk_PhotoPutZoomedBlock works like Tk_PhotoPutBlock except that the
197 image can be reduced or enlarged for display. The subsampleX and sub‐
198 sampleY parameters allow the size of the image to be reduced by subsam‐
199 pling. Tk_PhotoPutZoomedBlock will use only pixels from the input
200 image whose X coordinates are multiples of subsampleX, and whose Y
201 coordinates are multiples of subsampleY. For example, an image of
202 512x512 pixels can be reduced to 256x256 by setting subsampleX and sub‐
203 sampleY to 2.
204 The zoomX and zoomY parameters allow the image to be enlarged by pixel
206 replication. Each pixel of the (possibly subsampled) input image will
207 be written to a block zoomX pixels wide and zoomY pixels high of the
208 displayed image. Subsampling and zooming can be used together for spe‐
209 cial effects.
210 Tk_PhotoGetImage can be used to retrieve image data from a photo image.
212 Tk_PhotoGetImage fills in the structure pointed to by the blockPtr
213 parameter with values that describe the address and layout of the image
214 data that the photo image has stored internally. The values are valid
215 until the image is destroyed or its size is changed.
216 It is possible to modify an image by writing directly to the data the
218 pixelPtr field points to. The size of the image cannot be changed this
219 way, though. Also, changes made by writing directly to pixelPtr will
220 not be immediately visible, but only after a call to Tk_ImageChanged or
221 after an event that causes the interested widgets to redraw themselves.
222 For these reasons usually it is preferable to make changes to a copy of
223 the image data and write it back with Tk_PhotoPutBlock or Tk_PhotoPut‐
224 ZoomedBlock.
225 Tk_PhotoGetImage returns 1 for compatibility with the corresponding
227 procedure in the old photo widget.
228 Tk_PhotoBlank blanks the entire area of the photo image. Blank areas
230 of a photo image are transparent.
231 Tk_PhotoExpand requests that the widget's image be expanded to be at
233 least width x height pixels in size. The width and/or height are
234 unchanged if the user has specified an explicit image width or height
235 with the -width and/or -height configuration options, respectively. If
236 the image data are being supplied in many small blocks, it is more
237 efficient to use Tk_PhotoExpand or Tk_PhotoSetSize at the beginning
238 rather than allowing the image to expand in many small increments as
239 image blocks are supplied.
240 Tk_PhotoExpand normally returns TCL_OK, though if it cannot allocate
242 sufficient memory to hold the resulting image, TCL_ERROR is returned
243 instead and, if the interp argument is non-NULL, an error message is
244 placed in the interpreter's result.
245 Tk_PhotoSetSize specifies the size of the image, as if the user had
247 specified the given width and height values to the -width and -height
248 configuration options. A value of zero for width or height does not
249 change the image's width or height, but allows the width or height to
250 be changed by subsequent calls to Tk_PhotoPutBlock, Tk_PhotoPutZoomed‐
251 Block or Tk_PhotoExpand.
252 Tk_PhotoSetSize normally returns TCL_OK, though if it cannot allocate
254 sufficient memory to hold the resulting image, TCL_ERROR is returned
255 instead and, if the interp argument is non-NULL, an error message is
256 placed in the interpreter's result.
257 Tk_PhotoGetSize returns the dimensions of the image in *widthPtr and
259 *heightPtr.
260
262 In Tk 8.3 and earlier, Tk_PhotoPutBlock and Tk_PhotoPutZoomedBlock had
263 different signatures. If you want to compile code that uses the old
264 interface against 8.4 without updating your code, compile it with the
265 flag -DUSE_COMPOSITELESS_PHOTO_PUT_BLOCK. Code linked using Stubs
266 against older versions of Tk will continue to work.
267 In Tk 8.4, Tk_PhotoPutBlock, Tk_PhotoPutZoomedBlock, Tk_PhotoExpand and
269 Tk_PhotoSetSize did not take an interp argument or return any result
270 code. If insufficient memory was available for an image, Tk would
271 panic. This behaviour is still supported if you compile your extension
272 with the additional flag -DUSE_PANIC_ON_PHOTO_ALLOC_FAILURE. Code
273 linked using Stubs against older versions of Tk will continue to work.
274
276 The Tk_PhotoImageBlock structure used to provide image data to Tk_Pho‐
277 toPutBlock promises great flexibility in the layout of the data (e.g.
278 separate planes for the red, green, blue and alpha channels). Unfortu‐
279 nately, the implementation fails to hold this promise. The problem is
280 that the pixelSize field is (incorrectly) used to determine whether the
281 image has an alpha channel. Currently, if the offset for the alpha
282 channel is greater or equal than pixelSize, tk_PhotoPutblock assumes no
283 alpha data is present and makes the image fully opaque. This means
284 that for layouts where the channels are separate (or any other exotic
285 layout where pixelSize has to be smaller than the alpha offset), the
286 alpha channel will not be read correctly. In order to be on the safe
287 side if this issue will be corrected in a future release, it is
288 strongly recommended you always provide alpha data - even if the image
289 has no transparency - and only use the "standard" layout with a pixel‐
290 Size of 2 for grayscale and 4 for RGB data with offsets of 0, 0, 0, 1
291 or 0, 1, 2, 3 respectively.
292
294 The code for the photo image type was developed by Paul Mackerras,
295 based on his earlier photo widget code.
296
298 photo, image
299Tk 8.0 Tk_FindPhoto(3)