1Tk_CreateItemType(3) Tk Library Procedures Tk_CreateItemType(3)
2______________________________________________________________________________
6
8 Tk_CreateItemType, Tk_GetItemTypes - define new kind of canvas item
9
11 #include <tk.h>
12 Tk_CreateItemType(typePtr)
14 Tk_ItemType *
16 Tk_GetItemTypes()
17
19 Tk_ItemType *typePtr (in) Structure that defines the new type
20 of canvas item.
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22
24 Tk_CreateItemType is invoked to define a new kind of canvas item
25 described by the typePtr argument. An item type corresponds to a par‐
26 ticular value of the type argument to the create widget command for
27 canvases, and the code that implements a canvas item type is called a
28 type manager. Tk defines several built-in item types, such as rectan‐
29 gle and text and image, but Tk_CreateItemType allows additional item
30 types to be defined. Once Tk_CreateItemType returns, the new item type
31 may be used in new or existing canvas widgets just like the built-in
32 item types.
33 Tk_GetItemTypes returns a pointer to the first in the list of all item
35 types currently defined for canvases. The entries in the list are
36 linked together through their nextPtr fields, with the end of the list
37 marked by a NULL nextPtr.
38 You may find it easier to understand the rest of this manual entry by
40 looking at the code for an existing canvas item type such as bitmap (in
41 the file tkCanvBmap.c) or text (tkCanvText.c). The easiest way to cre‐
42 ate a new type manager is to copy the code for an existing type and
43 modify it for the new type.
44 Tk provides a number of utility procedures for the use of canvas type
46 managers, such as Tk_CanvasCoords and Tk_CanvasPsColor; these are
47 described in separate manual entries.
48
50 A type manager consists of a collection of procedures that provide a
51 standard set of operations on items of that type. The type manager
52 deals with three kinds of data structures. The first data structure is
53 a Tk_ItemType; it contains information such as the name of the type and
54 pointers to the standard procedures implemented by the type manager:
55 typedef struct Tk_ItemType {
57 const char *name;
58 int itemSize;
59 Tk_ItemCreateProc *createProc;
60 const Tk_ConfigSpec *configSpecs;
61 Tk_ItemConfigureProc *configProc;
62 Tk_ItemCoordProc *coordProc;
63 Tk_ItemDeleteProc *deleteProc;
64 Tk_ItemDisplayProc *displayProc;
65 int alwaysRedraw;
66 Tk_ItemPointProc *pointProc;
67 Tk_ItemAreaProc *areaProc;
68 Tk_ItemPostscriptProc *postscriptProc;
69 Tk_ItemScaleProc *scaleProc;
70 Tk_ItemTranslateProc *translateProc;
71 Tk_ItemIndexProc *indexProc;
72 Tk_ItemCursorProc *icursorProc;
73 Tk_ItemSelectionProc *selectionProc;
74 Tk_ItemInsertProc *insertProc;
75 Tk_ItemDCharsProc *dCharsProc;
76 Tk_ItemType *nextPtr;
77 } Tk_ItemType;
78 The fields of a Tk_ItemType structure are described in more detail
80 later in this manual entry. When Tk_CreateItemType is called, its
81 typePtr argument must point to a structure with all of the fields ini‐
82 tialized except nextPtr, which Tk sets to link all the types together
83 into a list. The structure must be in permanent memory (either stati‐
84 cally allocated or dynamically allocated but never freed); Tk retains a
85 pointer to this structure.
86 The second data structure manipulated by a type manager is an item
88 record. For each item in a canvas there exists one item record. All
89 of the items of a given type generally have item records with the same
90 structure, but different types usually have different formats for their
91 item records. The first part of each item record is a header with a
92 standard structure defined by Tk via the type Tk_Item; the rest of the
93 item record is defined by the type manager. A type manager must define
94 its item records with a Tk_Item as the first field. For example, the
95 item record for bitmap items is defined as follows:
96 typedef struct BitmapItem {
98 Tk_Item header;
99 double x, y;
100 Tk_Anchor anchor;
101 Pixmap bitmap;
102 XColor *fgColor;
103 XColor *bgColor;
104 GC gc;
105 } BitmapItem;
106 The header substructure contains information used by Tk to manage the
108 item, such as its identifier, its tags, its type, and its bounding box.
109 The fields starting with x belong to the type manager: Tk will never
110 read or write them. The type manager should not need to read or write
111 any of the fields in the header except for four fields whose names are
112 x1, y1, x2, and y2. These fields give a bounding box for the items
113 using integer canvas coordinates: the item should not cover any pixels
114 with x-coordinate lower than x1 or y-coordinate lower than y1, nor
115 should it cover any pixels with x-coordinate greater than or equal to
116 x2 or y-coordinate greater than or equal to y2. It is up to the type
117 manager to keep the bounding box up to date as the item is moved and
118 reconfigured.
119 Whenever Tk calls a procedure in a type manager it passes in a pointer
121 to an item record. The argument is always passed as a pointer to a
122 Tk_Item; the type manager will typically cast this into a pointer to
123 its own specific type, such as BitmapItem.
124 The third data structure used by type managers has type Tk_Canvas; it
126 serves as an opaque handle for the canvas widget as a whole. Type man‐
127 agers need not know anything about the contents of this structure. A
128 Tk_Canvas handle is typically passed in to the procedures of a type
129 manager, and the type manager can pass the handle back to library pro‐
130 cedures such as Tk_CanvasTkwin to fetch information about the canvas.
131
133 NAME
134 This section and the ones that follow describe each of the fields in a
135 Tk_ItemType structure in detail. The name field provides a string name
136 for the item type. Once Tk_CreateImageType returns, this name may be
137 used in create widget commands to create items of the new type. If
138 there already existed an item type by this name then the new item type
139 replaces the old one.
140 FLAGS (IN ALWAYSREDRAW)
142 The typePtr->alwaysRedraw field (so named for historic reasons) con‐
143 tains a collection of flag bits that modify how the canvas core inter‐
144 acts with the item. The following bits are defined:
145 1 Indicates that the item should always be redrawn when any part
147 of the canvas is redrawn, rather than only when the bounding box
148 of the item overlaps the area being redrawn. This is used by
149 window items, for example, which need to unmap subwindows that
150 are not on the screen.
151 TK_CONFIG_OBJS
153 Indicates that operations which would otherwise take a string
154 (or array of strings) actually take a Tcl_Obj reference (or an
155 array of such references). The operations to which this applies
156 are the configProc, the coordProc, the createProc, the indexProc
157 and the insertProc.
158 TK_MOVABLE_POINTS
160 Indicates that the item supports the dCharsProc, indexProc and │
161 insertProc with the same semantics as Tk's built-in line and │
162 polygon types, and that hence individual coordinate points can │
163 be moved. Must not be set if any of the above methods is NULL.
164 ITEMSIZE
166 typePtr->itemSize gives the size in bytes of item records of this type,
167 including the Tk_Item header. Tk uses this size to allocate memory
168 space for items of the type. All of the item records for a given type
169 must have the same size. If variable length fields are needed for an
170 item (such as a list of points for a polygon), the type manager can
171 allocate a separate object of variable length and keep a pointer to it
172 in the item record.
173 CREATEPROC
175 typePtr->createProc points to a procedure for Tk to call whenever a new
176 item of this type is created. typePtr->createProc must match the fol‐
177 lowing prototype:
178 typedef int Tk_ItemCreateProc(
180 Tcl_Interp *interp,
181 Tk_Canvas canvas,
182 Tk_Item *itemPtr,
183 int objc,
184 Tcl_Obj *const objv[]);
185 The interp argument is the interpreter in which the canvas's create
187 widget command was invoked, and canvas is a handle for the canvas wid‐
188 get. itemPtr is a pointer to a newly-allocated item of size type‐
189 Ptr->itemSize. Tk has already initialized the item's header (the first
190 sizeof(Tk_ItemType) bytes). The objc and objv arguments describe all
191 of the arguments to the create command after the type argument. Note
192 that if TK_CONFIG_OBJS is not set in the typePtr->alwaysRedraw field,
193 the objv parameter will actually contain a pointer to an array of con‐
194 stant strings. For example, in the widget command:
195 .c create rectangle 10 20 50 50 -fill black
197 objc will be 6 and objv[0] will contain the integer object 10.
199 createProc should use objc and objv to initialize the type-specific
201 parts of the item record and set an initial value for the bounding box
202 in the item's header. It should return a standard Tcl completion code
203 and leave an error message in the interpreter result if an error
204 occurs. If an error occurs Tk will free the item record, so createProc
205 must be sure to leave the item record in a clean state if it returns an
206 error (e.g., it must free any additional memory that it allocated for
207 the item).
208 CONFIGSPECS
210 Each type manager must provide a standard table describing its configu‐
211 ration options, in a form suitable for use with Tk_ConfigureWidget.
212 This table will normally be used by typePtr->createProc and type‐
213 Ptr->configProc, but Tk also uses it directly to retrieve option infor‐
214 mation in the itemcget and itemconfigure widget commands. type‐
215 Ptr->configSpecs must point to the configuration table for this type.
216 Note: Tk provides a custom option type tk_CanvasTagsOption for imple‐
217 menting the -tags option; see an existing type manager for an example
218 of how to use it in configSpecs.
219 CONFIGPROC
221 typePtr->configProc is called by Tk whenever the itemconfigure widget
222 command is invoked to change the configuration options for a canvas
223 item. This procedure must match the following prototype:
224 typedef int Tk_ItemConfigureProc(
226 Tcl_Interp *interp,
227 Tk_Canvas canvas,
228 Tk_Item *itemPtr,
229 int objc,
230 Tcl_Obj *const objv[],
231 int flags);
232 The interp argument identifies the interpreter in which the widget com‐
234 mand was invoked, canvas is a handle for the canvas widget, and itemPtr
235 is a pointer to the item being configured. objc and objv contain the
236 configuration options. Note that if TK_CONFIG_OBJS is not set in the
237 typePtr->alwaysRedraw field, the objv parameter will actually contain a
238 pointer to an array of constant strings. For example, if the following
239 command is invoked:
240 .c itemconfigure 2 -fill red -outline black
242 objc is 4 and objv contains the string objects -fill through black.
244 objc will always be an even value. The flags argument contains flags
245 to pass to Tk_ConfigureWidget; currently this value is always TK_CON‐
246 FIG_ARGV_ONLY when Tk invokes typePtr->configProc, but the type man‐
247 ager's createProc procedure will usually invoke configProc with differ‐
248 ent flag values.
249 typePtr->configProc returns a standard Tcl completion code and leaves
251 an error message in the interpreter result if an error occurs. It must
252 update the item's bounding box to reflect the new configuration
253 options.
254 COORDPROC
256 typePtr->coordProc is invoked by Tk to implement the coords widget com‐
257 mand for an item. It must match the following prototype:
258 typedef int Tk_ItemCoordProc(
260 Tcl_Interp *interp,
261 Tk_Canvas canvas,
262 Tk_Item *itemPtr,
263 int objc,
264 Tcl_Obj *const objv[]);
265 The arguments interp, canvas, and itemPtr all have the standard mean‐
267 ings, and objc and objv describe the coordinate arguments. Note that
268 if TK_CONFIG_OBJS is not set in the typePtr->alwaysRedraw field, the
269 objv parameter will actually contain a pointer to an array of constant
270 strings. For example, if the following widget command is invoked:
271 .c coords 2 30 90
273 objc will be 2 and objv will contain the integer objects 30 and 90.
275 The coordProc procedure should process the new coordinates, update the
277 item appropriately (e.g., it must reset the bounding box in the item's
278 header), and return a standard Tcl completion code. If an error
279 occurs, coordProc must leave an error message in the interpreter
280 result.
281 DELETEPROC
283 typePtr->deleteProc is invoked by Tk to delete an item and free any
284 resources allocated to it. It must match the following prototype:
285 typedef void Tk_ItemDeleteProc(
287 Tk_Canvas canvas,
288 Tk_Item *itemPtr,
289 Display *display);
290 The canvas and itemPtr arguments have the usual interpretations, and
292 display identifies the X display containing the canvas. deleteProc
293 must free up any resources allocated for the item, so that Tk can free
294 the item record. deleteProc should not actually free the item record;
295 this will be done by Tk when deleteProc returns.
296 DISPLAYPROC
298 typePtr->displayProc is invoked by Tk to redraw an item on the screen.
299 It must match the following prototype:
300 typedef void Tk_ItemDisplayProc(
302 Tk_Canvas canvas,
303 Tk_Item *itemPtr,
304 Display *display,
305 Drawable dst,
306 int x,
307 int y,
308 int width,
309 int height);
310 The canvas and itemPtr arguments have the usual meaning. display iden‐
312 tifies the display containing the canvas, and dst specifies a drawable
313 in which the item should be rendered; typically this is an off-screen
314 pixmap, which Tk will copy into the canvas's window once all relevant
315 items have been drawn. x, y, width, and height specify a rectangular
316 region in canvas coordinates, which is the area to be redrawn; only
317 information that overlaps this area needs to be redrawn. Tk will not
318 call displayProc unless the item's bounding box overlaps the redraw
319 area, but the type manager may wish to use the redraw area to optimize
320 the redisplay of the item.
321 Because of scrolling and the use of off-screen pixmaps for double-
323 buffered redisplay, the item's coordinates in dst will not necessarily
324 be the same as those in the canvas. displayProc should call Tk_Canvas‐
325 DrawableCoords to transform coordinates from those of the canvas to
326 those of dst.
327 Normally an item's displayProc is only invoked if the item overlaps the
329 area being displayed. However, if bit zero of typePtr->alwaysRedraw is
330 1, (i.e. “typePtr->alwaysRedraw & 1 == 1”) then displayProc is invoked
331 during every redisplay operation, even if the item does not overlap the
332 area of redisplay; this is useful for cases such as window items, where
333 the subwindow needs to be unmapped when it is off the screen.
334 POINTPROC
336 typePtr->pointProc is invoked by Tk to find out how close a given point
337 is to a canvas item. Tk uses this procedure for purposes such as
338 locating the item under the mouse or finding the closest item to a
339 given point. The procedure must match the following prototype:
340 typedef double Tk_ItemPointProc(
342 Tk_Canvas canvas,
343 Tk_Item *itemPtr,
344 double *pointPtr);
345 canvas and itemPtr have the usual meaning. pointPtr points to an array
347 of two numbers giving the x and y coordinates of a point. pointProc
348 must return a real value giving the distance from the point to the
349 item, or 0 if the point lies inside the item.
350 AREAPROC
352 typePtr->areaProc is invoked by Tk to find out the relationship between
353 an item and a rectangular area. It must match the following prototype:
354 typedef int Tk_ItemAreaProc(
356 Tk_Canvas canvas,
357 Tk_Item *itemPtr,
358 double *rectPtr);
359 canvas and itemPtr have the usual meaning. rectPtr points to an array
361 of four real numbers; the first two give the x and y coordinates of the
362 upper left corner of a rectangle, and the second two give the x and y
363 coordinates of the lower right corner. areaProc must return -1 if the
364 item lies entirely outside the given area, 0 if it lies partially
365 inside and partially outside the area, and 1 if it lies entirely inside
366 the area.
367 POSTSCRIPTPROC
369 typePtr->postscriptProc is invoked by Tk to generate Postscript for an
370 item during the postscript widget command. If the type manager is not
371 capable of generating Postscript then typePtr->postscriptProc should be
372 NULL. The procedure must match the following prototype:
373 typedef int Tk_ItemPostscriptProc(
375 Tcl_Interp *interp,
376 Tk_Canvas canvas,
377 Tk_Item *itemPtr,
378 int prepass);
379 The interp, canvas, and itemPtr arguments all have standard meanings;
381 prepass will be described below. If postscriptProc completes success‐
382 fully, it should append Postscript for the item to the information in
383 the interpreter result (e.g. by calling Tcl_AppendResult, not
384 Tcl_SetResult) and return TCL_OK. If an error occurs, postscriptProc
385 should clear the result and replace its contents with an error message;
386 then it should return TCL_ERROR.
387 Tk provides a collection of utility procedures to simplify postscript‐
389 Proc. For example, Tk_CanvasPsColor will generate Postscript to set
390 the current color to a given Tk color and Tk_CanvasPsFont will set up
391 font information. When generating Postscript, the type manager is free
392 to change the graphics state of the Postscript interpreter, since Tk
393 places gsave and grestore commands around the Postscript for the item.
394 The type manager can use canvas x coordinates directly in its Post‐
395 script, but it must call Tk_CanvasPsY to convert y coordinates from the
396 space of the canvas (where the origin is at the upper left) to the
397 space of Postscript (where the origin is at the lower left).
398 In order to generate Postscript that complies with the Adobe Document
400 Structuring Conventions, Tk actually generates Postscript in two
401 passes. It calls each item's postscriptProc in each pass. The only
402 purpose of the first pass is to collect font information (which is done
403 by Tk_CanvasPsFont); the actual Postscript is discarded. Tk sets the
404 prepass argument to postscriptProc to 1 during the first pass; the type
405 manager can use prepass to skip all Postscript generation except for
406 calls to Tk_CanvasPsFont. During the second pass prepass will be 0, so
407 the type manager must generate complete Postscript.
408 SCALEPROC
410 typePtr->scaleProc is invoked by Tk to rescale a canvas item during the
411 scale widget command. The procedure must match the following proto‐
412 type:
413 typedef void Tk_ItemScaleProc(
415 Tk_Canvas canvas,
416 Tk_Item *itemPtr,
417 double originX,
418 double originY,
419 double scaleX,
420 double scaleY);
421 The canvas and itemPtr arguments have the usual meaning. originX and
423 originY specify an origin relative to which the item is to be scaled,
424 and scaleX and scaleY give the x and y scale factors. The item should
425 adjust its coordinates so that a point in the item that used to have
426 coordinates x and y will have new coordinates x′ and y′, where
427 x′ = originX + scaleX × (x − originX)
429 y′ = originY + scaleY × (y − originY)
430 scaleProc must also update the bounding box in the item's header.
432 TRANSLATEPROC
434 typePtr->translateProc is invoked by Tk to translate a canvas item dur‐
435 ing the move widget command. The procedure must match the following
436 prototype:
437 typedef void Tk_ItemTranslateProc(
439 Tk_Canvas canvas,
440 Tk_Item *itemPtr,
441 double deltaX,
442 double deltaY);
443 The canvas and itemPtr arguments have the usual meaning, and deltaX and
445 deltaY give the amounts that should be added to each x and y coordinate
446 within the item. The type manager should adjust the item's coordinates
447 and update the bounding box in the item's header.
448 INDEXPROC
450 typePtr->indexProc is invoked by Tk to translate a string index speci‐
451 fication into a numerical index, for example during the index widget
452 command. It is only relevant for item types that support indexable
453 text or coordinates; typePtr->indexProc may be specified as NULL for
454 non-textual item types if they do not support detailed coordinate
455 addressing. The procedure must match the following prototype:
456 typedef int Tk_ItemIndexProc(
458 Tcl_Interp *interp,
459 Tk_Canvas canvas,
460 Tk_Item *itemPtr,
461 Tcl_Obj *indexObj,
462 int *indexPtr);
463 The interp, canvas, and itemPtr arguments all have the usual meaning.
465 indexObj contains a textual description of an index, and indexPtr
466 points to an integer value that should be filled in with a numerical
467 index. Note that if TK_CONFIG_OBJS is not set in the type‐
468 Ptr->alwaysRedraw field, the indexObj parameter will actually contain a
469 pointer to a constant string. It is up to the type manager to decide
470 what forms of index are supported (e.g., numbers, insert, sel.first,
471 end, etc.). indexProc should return a Tcl completion code and set the
472 interpreter result in the event of an error.
473 ICURSORPROC
475 typePtr->icursorProc is invoked by Tk during the icursor widget command
476 to set the position of the insertion cursor in a textual item. It is
477 only relevant for item types that support an insertion cursor; type‐
478 Ptr->icursorProc may be specified as NULL for item types that do not
479 support an insertion cursor. The procedure must match the following
480 prototype:
481 typedef void Tk_ItemCursorProc(
483 Tk_Canvas canvas,
484 Tk_Item *itemPtr,
485 int index);
486 canvas and itemPtr have the usual meanings, and index is an index into
488 the item's text, as returned by a previous call to typePtr->insertProc.
489 The type manager should position the insertion cursor in the item just
490 before the character given by index. Whether or not to actually dis‐
491 play the insertion cursor is determined by other information provided
492 by Tk_CanvasGetTextInfo.
493 SELECTIONPROC
495 typePtr->selectionProc is invoked by Tk during selection retrievals; it
496 must return part or all of the selected text in the item (if any). It
497 is only relevant for item types that support text; typePtr->selection‐
498 Proc may be specified as NULL for non-textual item types. The proce‐
499 dure must match the following prototype:
500 typedef int Tk_ItemSelectionProc(
502 Tk_Canvas canvas,
503 Tk_Item *itemPtr,
504 int offset,
505 char *buffer,
506 int maxBytes);
507 canvas and itemPtr have the usual meanings. offset is an offset in
509 bytes into the selection where 0 refers to the first byte of the selec‐
510 tion; it identifies the first character that is to be returned in this
511 call. buffer points to an area of memory in which to store the
512 requested bytes, and maxBytes specifies the maximum number of bytes to
513 return. selectionProc should extract up to maxBytes characters from
514 the selection and copy them to maxBytes; it should return a count of
515 the number of bytes actually copied, which may be less than maxBytes if
516 there are not offset+maxBytes bytes in the selection.
517 INSERTPROC
519 typePtr->insertProc is invoked by Tk during the insert widget command
520 to insert new text or coordinates into a canvas item. It is only rele‐
521 vant for item types that support the insert method; typePtr->insertProc
522 may be specified as NULL for other item types. The procedure must
523 match the following prototype:
524 typedef void Tk_ItemInsertProc(
526 Tk_Canvas canvas,
527 Tk_Item *itemPtr,
528 int index,
529 Tcl_Obj *obj);
530 canvas and itemPtr have the usual meanings. index is an index into the
532 item's text, as returned by a previous call to typePtr->insertProc, and
533 obj contains new text to insert just before the character given by
534 index. Note that if TK_CONFIG_OBJS is not set in the type‐
535 Ptr->alwaysRedraw field, the obj parameter will actually contain a
536 pointer to a constant string to be inserted. If the item supports mod‐
537 ification of the coordinates list by this
538 The type manager should insert the text and recompute the bounding box
540 in the item's header.
541 DCHARSPROC
543 typePtr->dCharsProc is invoked by Tk during the dchars widget command
544 to delete a range of text from a canvas item or a range of coordinates
545 from a pathed item. It is only relevant for item types that support
546 text; typePtr->dCharsProc may be specified as NULL for non-textual item
547 types that do not want to support coordinate deletion. The procedure
548 must match the following prototype:
549 typedef void Tk_ItemDCharsProc(
551 Tk_Canvas canvas,
552 Tk_Item *itemPtr,
553 int first,
554 int last);
555 canvas and itemPtr have the usual meanings. first and last give the
557 indices of the first and last bytes to be deleted, as returned by pre‐
558 vious calls to typePtr->indexProc. The type manager should delete the
559 specified characters and update the bounding box in the item's header.
560
562 Tk_CanvasPsY, Tk_CanvasTextInfo, Tk_CanvasTkwin
563
565 canvas, focus, item type, selection, type manager
566Tk 4.0 Tk_CreateItemType(3)