1Tk_CreateImageType(3) Tk Library Procedures Tk_CreateImageType(3)
2______________________________________________________________________________
6
8 Tk_CreateImageType, Tk_GetImageMasterData, Tk_InitImageArgs - define
9 new kind of image
10
12 #include <tk.h>
13 Tk_CreateImageType(typePtr)
15 ClientData
17 Tk_GetImageMasterData(interp, name, typePtrPtr)
18 Tk_InitImageArgs(interp, argc, argvPtr)
20
22 Tk_ImageType *typePtr (in) Structure that defines the new
23 type of image. Must be static:
24 a pointer to this structure is
25 retained by the image code.
26 Tcl_Interp *interp (in) Interpreter in which image was
28 created.
29 const char *name (in) Name of existing image.
31 Tk_ImageType **typePtrPtr (out) Points to word in which to store
33 a pointer to type information
34 for the given image, if it
35 exists.
36 int argc (in) Number of arguments
38 char ***argvPtr (in/out) Pointer to argument list
40_________________________________________________________________
41
44 Tk_CreateImageType is invoked to define a new kind of image. An image
45 type corresponds to a particular value of the type argument for the
46 image create command. There may exist any number of different image
47 types, and new types may be defined dynamically by calling Tk_CreateIm‐
48 ageType. For example, there might be one type for 2-color bitmaps,
49 another for multi-color images, another for dithered images, another
50 for video, and so on.
51 The code that implements a new image type is called an image manager.
53 It consists of a collection of procedures plus three different kinds of
54 data structures. The first data structure is a Tk_ImageType structure,
55 which contains the name of the image type and pointers to five proce‐
56 dures provided by the image manager to deal with images of this type:
57 typedef struct Tk_ImageType {
58 char *name;
59 Tk_ImageCreateProc *createProc;
60 Tk_ImageGetProc *getProc;
61 Tk_ImageDisplayProc *displayProc;
62 Tk_ImageFreeProc *freeProc;
63 Tk_ImageDeleteProc *deleteProc;
64 } Tk_ImageType;
65 The fields of this structure will be described in later subsections of
66 this entry.
67 The second major data structure manipulated by an image manager is
69 called an image master; it contains overall information about a par‐
70 ticular image, such as the values of the configuration options speci‐
71 fied in an image create command. There will usually be one of these
72 structures for each invocation of the image create command.
73 The third data structure related to images is an image instance. There
75 will usually be one of these structures for each usage of an image in a
76 particular widget. It is possible for a single image to appear simul‐
77 taneously in multiple widgets, or even multiple times in the same wid‐
78 get. Furthermore, different instances may be on different screens or
79 displays. The image instance data structure describes things that may
80 vary from instance to instance, such as colors and graphics contexts
81 for redisplay. There is usually one instance structure for each -image
82 option specified for a widget or canvas item.
83 The following subsections describe the fields of a Tk_ImageType in more
85 detail.
86 NAME
89 typePtr->name provides a name for the image type. Once Tk_CreateIm‐
90 ageType returns, this name may be used in image create commands to cre‐
91 ate images of the new type. If there already existed an image type by
92 this name then the new image type replaces the old one.
93 CREATEPROC
96 typePtr->createProc provides the address of a procedure for Tk to call
97 whenever image create is invoked to create an image of the new type.
98 typePtr->createProc must match the following prototype:
99 typedef int Tk_ImageCreateProc(
100 Tcl_Interp *interp,
101 char *name,
102 int objc,
103 Tcl_Obj *const objv[],
104 Tk_ImageType *typePtr,
105 Tk_ImageMaster master,
106 ClientData *masterDataPtr);
107 The interp argument is the interpreter in which the image command was
108 invoked, and name is the name for the new image, which was either spec‐
109 ified explicitly in the image command or generated automatically by the
110 image command. The objc and objv arguments describe all the configura‐
111 tion options for the new image (everything after the name argument to
112 image). The master argument is a token that refers to Tk's information
113 about this image; the image manager must return this token to Tk when
114 invoking the Tk_ImageChanged procedure. Typically createProc will
115 parse objc and objv and create an image master data structure for the
116 new image. createProc may store an arbitrary one-word value at *mas‐
117 terDataPtr, which will be passed back to the image manager when other
118 callbacks are invoked. Typically the value is a pointer to the master
119 data structure for the image.
120 If createProc encounters an error, it should leave an error message in
122 the interpreter result and return TCL_ERROR; otherwise it should
123 return TCL_OK.
124 createProc should call Tk_ImageChanged in order to set the size of the
126 image and request an initial redisplay.
127 GETPROC
130 typePtr->getProc is invoked by Tk whenever a widget calls Tk_GetImage
131 to use a particular image. This procedure must match the following
132 prototype:
133 typedef ClientData Tk_ImageGetProc(
134 Tk_Window tkwin,
135 ClientData masterData);
136 The tkwin argument identifies the window in which the image will be
137 used and masterData is the value returned by createProc when the image
138 master was created. getProc will usually create a data structure for
139 the new instance, including such things as the resources needed to dis‐
140 play the image in the given window. getProc returns a one-word token
141 for the instance, which is typically the address of the instance data
142 structure. Tk will pass this value back to the image manager when
143 invoking its displayProc and freeProc procedures.
144 DISPLAYPROC
147 typePtr->displayProc is invoked by Tk whenever an image needs to be
148 displayed (i.e., whenever a widget calls Tk_RedrawImage). displayProc
149 must match the following prototype:
150 typedef void Tk_ImageDisplayProc(
151 ClientData instanceData,
152 Display *display,
153 Drawable drawable,
154 int imageX,
155 int imageY,
156 int width,
157 int height,
158 int drawableX,
159 int drawableY);
160 The instanceData will be the same as the value returned by getProc when
161 the instance was created. display and drawable indicate where to dis‐
162 play the image; drawable may be a pixmap rather than the window speci‐
163 fied to getProc (this is usually the case, since most widgets double-
164 buffer their redisplay to get smoother visual effects). imageX,
165 imageY, width, and height identify the region of the image that must be
166 redisplayed. This region will always be within the size of the image
167 as specified in the most recent call to Tk_ImageChanged. drawableX and
168 drawableY indicate where in drawable the image should be displayed;
169 displayProc should display the given region of the image so that point
170 (imageX, imageY) in the image appears at (drawableX, drawableY) in
171 drawable.
172 FREEPROC
175 typePtr->freeProc contains the address of a procedure that Tk will
176 invoke when an image instance is released (i.e., when Tk_FreeImage is
177 invoked). This can happen, for example, when a widget is deleted or a
178 image item in a canvas is deleted, or when the image displayed in a
179 widget or canvas item is changed. freeProc must match the following
180 prototype:
181 typedef void Tk_ImageFreeProc(
182 ClientData instanceData,
183 Display *display);
184 The instanceData will be the same as the value returned by getProc when
185 the instance was created, and display is the display containing the
186 window for the instance. freeProc should release any resources associ‐
187 ated with the image instance, since the instance will never be used
188 again.
189 DELETEPROC
192 typePtr->deleteProc is a procedure that Tk invokes when an image is
193 being deleted (i.e. when the image delete command is invoked). Before
194 invoking deleteProc Tk will invoke freeProc for each of the image's
195 instances. deleteProc must match the following prototype:
196 typedef void Tk_ImageDeleteProc(
197 ClientData masterData);
198 The masterData argument will be the same as the value stored in *mas‐
199 terDataPtr by createProc when the image was created. deleteProc should
200 release any resources associated with the image.
201
204 The procedure Tk_GetImageMasterData may be invoked to retrieve informa‐
205 tion about an image. For example, an image manager can use this proce‐
206 dure to locate its image master data for an image. If there exists an
207 image named name in the interpreter given by interp, then *typePtrPtr
208 is filled in with type information for the image (the typePtr value
209 passed to Tk_CreateImageType when the image type was registered) and
210 the return value is the ClientData value returned by the createProc
211 when the image was created (this is typically a pointer to the image
212 master data structure). If no such image exists then NULL is returned
213 and NULL is stored at *typePtrPtr.
214
217 In Tk 8.2 and earlier, the definition of Tk_ImageCreateProc was incom‐
218 patibly different, with the following prototype:
219 typedef int Tk_ImageCreateProc(
220 Tcl_Interp *interp,
221 char *name,
222 int argc,
223 char **argv,
224 Tk_ImageType *typePtr,
225 Tk_ImageMaster master,
226 ClientData *masterDataPtr);
227 Legacy programs and libraries dating from those days may still contain
228 code that defines extended Tk image types using the old interface. The
229 Tk header file will still support this legacy interface if the code is
230 compiled with the macro USE_OLD_IMAGE defined.
231 When the USE_OLD_IMAGE legacy support is enabled, you may see the rou‐
233 tine Tk_InitImageArgs in use. This was a migration tool used to create
234 stub-enabled extensions that could be loaded into interps containing
235 all versions of Tk 8.1 and later. Tk 8.5 no longer provides this rou‐
236 tine, but uses a macro to convert any attempted calls of this routine
237 into an empty comment. Any stub-enabled extension providing an
238 extended image type via the legacy interface that is compiled against
239 Tk 8.5 headers and linked against the Tk 8.5 stub library will produce
240 a file that can be loaded only into interps with Tk 8.5 or later; that
241 is, the normal stub-compatibility rules. If a developer needs to gen‐
242 erate from such code a file that is loadable into interps with Tk 8.4
243 or earlier, they must use Tk 8.4 headers and stub libraries to do so.
244 Any new code written today should not make use of the legacy inter‐
246 faces. Expect their support to go away in Tk 9.
247
250 Tk_ImageChanged, Tk_GetImage, Tk_FreeImage, Tk_RedrawImage, Tk_Size‐
251 OfImage
252
255 image manager, image type, instance, master
256Tk 8.5 Tk_CreateImageType(3)