mapper.js 24 KB

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  1. /**
  2. * @license Copyright (c) 2003-2019, CKSource - Frederico Knabben. All rights reserved.
  3. * For licensing, see LICENSE.md or https://ckeditor.com/legal/ckeditor-oss-license
  4. */
  5. /**
  6. * @module engine/conversion/mapper
  7. */
  8. import ModelPosition from '../model/position';
  9. import ModelRange from '../model/range';
  10. import ViewPosition from '../view/position';
  11. import ViewRange from '../view/range';
  12. import ViewText from '../view/text';
  13. import EmitterMixin from '@ckeditor/ckeditor5-utils/src/emittermixin';
  14. import mix from '@ckeditor/ckeditor5-utils/src/mix';
  15. /**
  16. * Maps elements, positions and markers between {@link module:engine/view/document~Document the view} and
  17. * {@link module:engine/model/model the model}.
  18. *
  19. * The instance of the Mapper used for the editing pipeline is available in
  20. * {@link module:engine/controller/editingcontroller~EditingController#mapper `editor.editing.mapper`}.
  21. *
  22. * Mapper uses bound elements to find corresponding elements and positions, so, to get proper results,
  23. * all model elements should be {@link module:engine/conversion/mapper~Mapper#bindElements bound}.
  24. *
  25. * To map complex model to/from view relations, you may provide custom callbacks for
  26. * {@link module:engine/conversion/mapper~Mapper#event:modelToViewPosition modelToViewPosition event} and
  27. * {@link module:engine/conversion/mapper~Mapper#event:viewToModelPosition viewToModelPosition event} that are fired whenever
  28. * a position mapping request occurs.
  29. * Those events are fired by {@link module:engine/conversion/mapper~Mapper#toViewPosition toViewPosition}
  30. * and {@link module:engine/conversion/mapper~Mapper#toModelPosition toModelPosition} methods. `Mapper` adds it's own default callbacks
  31. * with `'lowest'` priority. To override default `Mapper` mapping, add custom callback with higher priority and
  32. * stop the event.
  33. */
  34. export default class Mapper {
  35. /**
  36. * Creates an instance of the mapper.
  37. */
  38. constructor() {
  39. /**
  40. * Model element to view element mapping.
  41. *
  42. * @private
  43. * @member {WeakMap}
  44. */
  45. this._modelToViewMapping = new WeakMap();
  46. /**
  47. * View element to model element mapping.
  48. *
  49. * @private
  50. * @member {WeakMap}
  51. */
  52. this._viewToModelMapping = new WeakMap();
  53. /**
  54. * A map containing callbacks between view element names and functions evaluating length of view elements
  55. * in model.
  56. *
  57. * @private
  58. * @member {Map}
  59. */
  60. this._viewToModelLengthCallbacks = new Map();
  61. /**
  62. * Model marker name to view elements mapping.
  63. *
  64. * Keys are `String`s while values are `Set`s with {@link module:engine/view/element~Element view elements}.
  65. * One marker (name) can be mapped to multiple elements.
  66. *
  67. * @private
  68. * @member {Map}
  69. */
  70. this._markerNameToElements = new Map();
  71. // Default mapper algorithm for mapping model position to view position.
  72. this.on( 'modelToViewPosition', ( evt, data ) => {
  73. if ( data.viewPosition ) {
  74. return;
  75. }
  76. const viewContainer = this._modelToViewMapping.get( data.modelPosition.parent );
  77. data.viewPosition = this._findPositionIn( viewContainer, data.modelPosition.offset );
  78. }, { priority: 'low' } );
  79. // Default mapper algorithm for mapping view position to model position.
  80. this.on( 'viewToModelPosition', ( evt, data ) => {
  81. if ( data.modelPosition ) {
  82. return;
  83. }
  84. const viewBlock = this.findMappedViewAncestor( data.viewPosition );
  85. const modelParent = this._viewToModelMapping.get( viewBlock );
  86. const modelOffset = this._toModelOffset( data.viewPosition.parent, data.viewPosition.offset, viewBlock );
  87. data.modelPosition = ModelPosition._createAt( modelParent, modelOffset );
  88. }, { priority: 'low' } );
  89. }
  90. /**
  91. * Marks model and view elements as corresponding. Corresponding elements can be retrieved by using
  92. * the {@link module:engine/conversion/mapper~Mapper#toModelElement toModelElement} and
  93. * {@link module:engine/conversion/mapper~Mapper#toViewElement toViewElement} methods.
  94. * The information that elements are bound is also used to translate positions.
  95. *
  96. * @param {module:engine/model/element~Element} modelElement Model element.
  97. * @param {module:engine/view/element~Element} viewElement View element.
  98. */
  99. bindElements( modelElement, viewElement ) {
  100. this._modelToViewMapping.set( modelElement, viewElement );
  101. this._viewToModelMapping.set( viewElement, modelElement );
  102. }
  103. /**
  104. * Unbinds given {@link module:engine/view/element~Element view element} from the map.
  105. *
  106. * **Note:** view-to-model binding will be removed, if it existed. However, corresponding model-to-view binding
  107. * will be removed only if model element is still bound to passed `viewElement`.
  108. *
  109. * This behavior lets for re-binding model element to another view element without fear of losing the new binding
  110. * when the previously bound view element is unbound.
  111. *
  112. * @param {module:engine/view/element~Element} viewElement View element to unbind.
  113. */
  114. unbindViewElement( viewElement ) {
  115. const modelElement = this.toModelElement( viewElement );
  116. this._viewToModelMapping.delete( viewElement );
  117. if ( this._modelToViewMapping.get( modelElement ) == viewElement ) {
  118. this._modelToViewMapping.delete( modelElement );
  119. }
  120. }
  121. /**
  122. * Unbinds given {@link module:engine/model/element~Element model element} from the map.
  123. *
  124. * **Note:** model-to-view binding will be removed, if it existed. However, corresponding view-to-model binding
  125. * will be removed only if view element is still bound to passed `modelElement`.
  126. *
  127. * This behavior lets for re-binding view element to another model element without fear of losing the new binding
  128. * when the previously bound model element is unbound.
  129. *
  130. * @param {module:engine/model/element~Element} modelElement Model element to unbind.
  131. */
  132. unbindModelElement( modelElement ) {
  133. const viewElement = this.toViewElement( modelElement );
  134. this._modelToViewMapping.delete( modelElement );
  135. if ( this._viewToModelMapping.get( viewElement ) == modelElement ) {
  136. this._viewToModelMapping.delete( viewElement );
  137. }
  138. }
  139. /**
  140. * Binds given marker name with given {@link module:engine/view/element~Element view element}. The element
  141. * will be added to the current set of elements bound with given marker name.
  142. *
  143. * @param {module:engine/view/element~Element} element Element to bind.
  144. * @param {String} name Marker name.
  145. */
  146. bindElementToMarker( element, name ) {
  147. const elements = this._markerNameToElements.get( name ) || new Set();
  148. elements.add( element );
  149. this._markerNameToElements.set( name, elements );
  150. }
  151. /**
  152. * Unbinds an element from given marker name.
  153. *
  154. * @param {module:engine/view/element~Element} element Element to unbind.
  155. * @param {String} name Marker name.
  156. */
  157. unbindElementFromMarkerName( element, name ) {
  158. const elements = this._markerNameToElements.get( name );
  159. if ( elements ) {
  160. elements.delete( element );
  161. if ( elements.size == 0 ) {
  162. this._markerNameToElements.delete( name );
  163. }
  164. }
  165. }
  166. /**
  167. * Removes all model to view and view to model bindings.
  168. */
  169. clearBindings() {
  170. this._modelToViewMapping = new WeakMap();
  171. this._viewToModelMapping = new WeakMap();
  172. this._markerNameToElements = new Map();
  173. }
  174. /**
  175. * Gets the corresponding model element.
  176. *
  177. * **Note:** {@link module:engine/view/uielement~UIElement} does not have corresponding element in model.
  178. *
  179. * @param {module:engine/view/element~Element} viewElement View element.
  180. * @returns {module:engine/model/element~Element|undefined} Corresponding model element or `undefined` if not found.
  181. */
  182. toModelElement( viewElement ) {
  183. return this._viewToModelMapping.get( viewElement );
  184. }
  185. /**
  186. * Gets the corresponding view element.
  187. *
  188. * @param {module:engine/model/element~Element} modelElement Model element.
  189. * @returns {module:engine/view/element~Element|undefined} Corresponding view element or `undefined` if not found.
  190. */
  191. toViewElement( modelElement ) {
  192. return this._modelToViewMapping.get( modelElement );
  193. }
  194. /**
  195. * Gets the corresponding model range.
  196. *
  197. * @param {module:engine/view/range~Range} viewRange View range.
  198. * @returns {module:engine/model/range~Range} Corresponding model range.
  199. */
  200. toModelRange( viewRange ) {
  201. return new ModelRange( this.toModelPosition( viewRange.start ), this.toModelPosition( viewRange.end ) );
  202. }
  203. /**
  204. * Gets the corresponding view range.
  205. *
  206. * @param {module:engine/model/range~Range} modelRange Model range.
  207. * @returns {module:engine/view/range~Range} Corresponding view range.
  208. */
  209. toViewRange( modelRange ) {
  210. return new ViewRange( this.toViewPosition( modelRange.start ), this.toViewPosition( modelRange.end ) );
  211. }
  212. /**
  213. * Gets the corresponding model position.
  214. *
  215. * @fires viewToModelPosition
  216. * @param {module:engine/view/position~Position} viewPosition View position.
  217. * @returns {module:engine/model/position~Position} Corresponding model position.
  218. */
  219. toModelPosition( viewPosition ) {
  220. const data = {
  221. viewPosition,
  222. mapper: this
  223. };
  224. this.fire( 'viewToModelPosition', data );
  225. return data.modelPosition;
  226. }
  227. /**
  228. * Gets the corresponding view position.
  229. *
  230. * @fires modelToViewPosition
  231. * @param {module:engine/model/position~Position} modelPosition Model position.
  232. * @param {Object} [options] Additional options for position mapping process.
  233. * @param {Boolean} [options.isPhantom=false] Should be set to `true` if the model position to map is pointing to a place
  234. * in model tree which no longer exists. For example, it could be an end of a removed model range.
  235. * @returns {module:engine/view/position~Position} Corresponding view position.
  236. */
  237. toViewPosition( modelPosition, options = { isPhantom: false } ) {
  238. const data = {
  239. modelPosition,
  240. mapper: this,
  241. isPhantom: options.isPhantom
  242. };
  243. this.fire( 'modelToViewPosition', data );
  244. return data.viewPosition;
  245. }
  246. /**
  247. * Gets all view elements bound to the given marker name.
  248. *
  249. * @param {String} name Marker name.
  250. * @returns {Set.<module:engine/view/element~Element>|null} View elements bound with given marker name or `null`
  251. * if no elements are bound to given marker name.
  252. */
  253. markerNameToElements( name ) {
  254. const boundElements = this._markerNameToElements.get( name );
  255. if ( !boundElements ) {
  256. return null;
  257. }
  258. const elements = new Set();
  259. for ( const element of boundElements ) {
  260. if ( element.is( 'attributeElement' ) ) {
  261. for ( const clone of element.getElementsWithSameId() ) {
  262. elements.add( clone );
  263. }
  264. } else {
  265. elements.add( element );
  266. }
  267. }
  268. return elements;
  269. }
  270. /**
  271. * Registers a callback that evaluates the length in the model of a view element with given name.
  272. *
  273. * The callback is fired with one argument, which is a view element instance. The callback is expected to return
  274. * a number representing the length of view element in model.
  275. *
  276. * // List item in view may contain nested list, which have other list items. In model though,
  277. * // the lists are represented by flat structure. Because of those differences, length of list view element
  278. * // may be greater than one. In the callback it's checked how many nested list items are in evaluated list item.
  279. *
  280. * function getViewListItemLength( element ) {
  281. * let length = 1;
  282. *
  283. * for ( let child of element.getChildren() ) {
  284. * if ( child.name == 'ul' || child.name == 'ol' ) {
  285. * for ( let item of child.getChildren() ) {
  286. * length += getViewListItemLength( item );
  287. * }
  288. * }
  289. * }
  290. *
  291. * return length;
  292. * }
  293. *
  294. * mapper.registerViewToModelLength( 'li', getViewListItemLength );
  295. *
  296. * @param {String} viewElementName Name of view element for which callback is registered.
  297. * @param {Function} lengthCallback Function return a length of view element instance in model.
  298. */
  299. registerViewToModelLength( viewElementName, lengthCallback ) {
  300. this._viewToModelLengthCallbacks.set( viewElementName, lengthCallback );
  301. }
  302. /**
  303. * For given `viewPosition`, finds and returns the closest ancestor of this position that has a mapping to
  304. * the model.
  305. *
  306. * @param {module:engine/view/position~Position} viewPosition Position for which mapped ancestor should be found.
  307. * @returns {module:engine/view/element~Element}
  308. */
  309. findMappedViewAncestor( viewPosition ) {
  310. let parent = viewPosition.parent;
  311. while ( !this._viewToModelMapping.has( parent ) ) {
  312. parent = parent.parent;
  313. }
  314. return parent;
  315. }
  316. /**
  317. * Calculates model offset based on the view position and the block element.
  318. *
  319. * Example:
  320. *
  321. * <p>foo<b>ba|r</b></p> // _toModelOffset( b, 2, p ) -> 5
  322. *
  323. * Is a sum of:
  324. *
  325. * <p>foo|<b>bar</b></p> // _toModelOffset( p, 3, p ) -> 3
  326. * <p>foo<b>ba|r</b></p> // _toModelOffset( b, 2, b ) -> 2
  327. *
  328. * @private
  329. * @param {module:engine/view/element~Element} viewParent Position parent.
  330. * @param {Number} viewOffset Position offset.
  331. * @param {module:engine/view/element~Element} viewBlock Block used as a base to calculate offset.
  332. * @returns {Number} Offset in the model.
  333. */
  334. _toModelOffset( viewParent, viewOffset, viewBlock ) {
  335. if ( viewBlock != viewParent ) {
  336. // See example.
  337. const offsetToParentStart = this._toModelOffset( viewParent.parent, viewParent.index, viewBlock );
  338. const offsetInParent = this._toModelOffset( viewParent, viewOffset, viewParent );
  339. return offsetToParentStart + offsetInParent;
  340. }
  341. // viewBlock == viewParent, so we need to calculate the offset in the parent element.
  342. // If the position is a text it is simple ("ba|r" -> 2).
  343. if ( viewParent.is( 'text' ) ) {
  344. return viewOffset;
  345. }
  346. // If the position is in an element we need to sum lengths of siblings ( <b> bar </b> foo | -> 3 + 3 = 6 ).
  347. let modelOffset = 0;
  348. for ( let i = 0; i < viewOffset; i++ ) {
  349. modelOffset += this.getModelLength( viewParent.getChild( i ) );
  350. }
  351. return modelOffset;
  352. }
  353. /**
  354. * Gets the length of the view element in the model.
  355. *
  356. * The length is calculated as follows:
  357. * * if {@link #registerViewToModelLength length mapping callback} is provided for given `viewNode` it is used to
  358. * evaluate model length (`viewNode` is used as first and only parameter passed to the callback),
  359. * * length of a {@link module:engine/view/text~Text text node} is equal to the length of it's
  360. * {@link module:engine/view/text~Text#data data},
  361. * * length of a {@link module:engine/view/uielement~UIElement ui element} is equal to 0,
  362. * * length of a mapped {@link module:engine/view/element~Element element} is equal to 1,
  363. * * length of a not-mapped {@link module:engine/view/element~Element element} is equal to the length of it's children.
  364. *
  365. * Examples:
  366. *
  367. * foo -> 3 // Text length is equal to it's data length.
  368. * <p>foo</p> -> 1 // Length of an element which is mapped is by default equal to 1.
  369. * <b>foo</b> -> 3 // Length of an element which is not mapped is a length of its children.
  370. * <div><p>x</p><p>y</p></div> -> 2 // Assuming that <div> is not mapped and <p> are mapped.
  371. *
  372. * @param {module:engine/view/element~Element} viewNode View node.
  373. * @returns {Number} Length of the node in the tree model.
  374. */
  375. getModelLength( viewNode ) {
  376. if ( this._viewToModelLengthCallbacks.get( viewNode.name ) ) {
  377. const callback = this._viewToModelLengthCallbacks.get( viewNode.name );
  378. return callback( viewNode );
  379. } else if ( this._viewToModelMapping.has( viewNode ) ) {
  380. return 1;
  381. } else if ( viewNode.is( 'text' ) ) {
  382. return viewNode.data.length;
  383. } else if ( viewNode.is( 'uiElement' ) ) {
  384. return 0;
  385. } else {
  386. let len = 0;
  387. for ( const child of viewNode.getChildren() ) {
  388. len += this.getModelLength( child );
  389. }
  390. return len;
  391. }
  392. }
  393. /**
  394. * Finds the position in the view node (or its children) with the expected model offset.
  395. *
  396. * Example:
  397. *
  398. * <p>fo<b>bar</b>bom</p> -> expected offset: 4
  399. *
  400. * _findPositionIn( p, 4 ):
  401. * <p>|fo<b>bar</b>bom</p> -> expected offset: 4, actual offset: 0
  402. * <p>fo|<b>bar</b>bom</p> -> expected offset: 4, actual offset: 2
  403. * <p>fo<b>bar</b>|bom</p> -> expected offset: 4, actual offset: 5 -> we are too far
  404. *
  405. * _findPositionIn( b, 4 - ( 5 - 3 ) ):
  406. * <p>fo<b>|bar</b>bom</p> -> expected offset: 2, actual offset: 0
  407. * <p>fo<b>bar|</b>bom</p> -> expected offset: 2, actual offset: 3 -> we are too far
  408. *
  409. * _findPositionIn( bar, 2 - ( 3 - 3 ) ):
  410. * We are in the text node so we can simple find the offset.
  411. * <p>fo<b>ba|r</b>bom</p> -> expected offset: 2, actual offset: 2 -> position found
  412. *
  413. * @private
  414. * @param {module:engine/view/element~Element} viewParent Tree view element in which we are looking for the position.
  415. * @param {Number} expectedOffset Expected offset.
  416. * @returns {module:engine/view/position~Position} Found position.
  417. */
  418. _findPositionIn( viewParent, expectedOffset ) {
  419. // Last scanned view node.
  420. let viewNode;
  421. // Length of the last scanned view node.
  422. let lastLength = 0;
  423. let modelOffset = 0;
  424. let viewOffset = 0;
  425. // In the text node it is simple: offset in the model equals offset in the text.
  426. if ( viewParent.is( 'text' ) ) {
  427. return new ViewPosition( viewParent, expectedOffset );
  428. }
  429. // In other cases we add lengths of child nodes to find the proper offset.
  430. // If it is smaller we add the length.
  431. while ( modelOffset < expectedOffset ) {
  432. viewNode = viewParent.getChild( viewOffset );
  433. lastLength = this.getModelLength( viewNode );
  434. modelOffset += lastLength;
  435. viewOffset++;
  436. }
  437. // If it equals we found the position.
  438. if ( modelOffset == expectedOffset ) {
  439. return this._moveViewPositionToTextNode( new ViewPosition( viewParent, viewOffset ) );
  440. }
  441. // If it is higher we need to enter last child.
  442. else {
  443. // ( modelOffset - lastLength ) is the offset to the child we enter,
  444. // so we subtract it from the expected offset to fine the offset in the child.
  445. return this._findPositionIn( viewNode, expectedOffset - ( modelOffset - lastLength ) );
  446. }
  447. }
  448. /**
  449. * Because we prefer positions in text nodes over positions next to text node moves view position to the text node
  450. * if it was next to it.
  451. *
  452. * <p>[]<b>foo</b></p> -> <p>[]<b>foo</b></p> // do not touch if position is not directly next to text
  453. * <p>foo[]<b>foo</b></p> -> <p>foo{}<b>foo</b></p> // move to text node
  454. * <p><b>[]foo</b></p> -> <p><b>{}foo</b></p> // move to text node
  455. *
  456. * @private
  457. * @param {module:engine/view/position~Position} viewPosition Position potentially next to text node.
  458. * @returns {module:engine/view/position~Position} Position in text node if possible.
  459. */
  460. _moveViewPositionToTextNode( viewPosition ) {
  461. // If the position is just after text node, put it at the end of that text node.
  462. // If the position is just before text node, put it at the beginning of that text node.
  463. const nodeBefore = viewPosition.nodeBefore;
  464. const nodeAfter = viewPosition.nodeAfter;
  465. if ( nodeBefore instanceof ViewText ) {
  466. return new ViewPosition( nodeBefore, nodeBefore.data.length );
  467. } else if ( nodeAfter instanceof ViewText ) {
  468. return new ViewPosition( nodeAfter, 0 );
  469. }
  470. // Otherwise, just return the given position.
  471. return viewPosition;
  472. }
  473. /**
  474. * Fired for each model-to-view position mapping request. The purpose of this event is to enable custom model-to-view position
  475. * mapping. Callbacks added to this event take {@link module:engine/model/position~Position model position} and are expected to
  476. * calculate {@link module:engine/view/position~Position view position}. Calculated view position should be added as `viewPosition`
  477. * value in `data` object that is passed as one of parameters to the event callback.
  478. *
  479. * // Assume that "captionedImage" model element is converted to <img> and following <span> elements in view,
  480. * // and the model element is bound to <img> element. Force mapping model positions inside "captionedImage" to that
  481. * // <span> element.
  482. * mapper.on( 'modelToViewPosition', ( evt, data ) => {
  483. * const positionParent = modelPosition.parent;
  484. *
  485. * if ( positionParent.name == 'captionedImage' ) {
  486. * const viewImg = data.mapper.toViewElement( positionParent );
  487. * const viewCaption = viewImg.nextSibling; // The <span> element.
  488. *
  489. * data.viewPosition = new ViewPosition( viewCaption, modelPosition.offset );
  490. *
  491. * // Stop the event if other callbacks should not modify calculated value.
  492. * evt.stop();
  493. * }
  494. * } );
  495. *
  496. * **Note:** keep in mind that sometimes a "phantom" model position is being converted. "Phantom" model position is
  497. * a position that points to a non-existing place in model. Such position might still be valid for conversion, though
  498. * (it would point to a correct place in view when converted). One example of such situation is when a range is
  499. * removed from model, there may be a need to map the range's end (which is no longer valid model position). To
  500. * handle such situation, check `data.isPhantom` flag:
  501. *
  502. * // Assume that there is "customElement" model element and whenever position is before it, we want to move it
  503. * // to the inside of the view element bound to "customElement".
  504. * mapper.on( 'modelToViewPosition', ( evt, data ) => {
  505. * if ( data.isPhantom ) {
  506. * return;
  507. * }
  508. *
  509. * // Below line might crash for phantom position that does not exist in model.
  510. * const sibling = data.modelPosition.nodeBefore;
  511. *
  512. * // Check if this is the element we are interested in.
  513. * if ( !sibling.is( 'customElement' ) ) {
  514. * return;
  515. * }
  516. *
  517. * const viewElement = data.mapper.toViewElement( sibling );
  518. *
  519. * data.viewPosition = new ViewPosition( sibling, 0 );
  520. *
  521. * evt.stop();
  522. * } );
  523. *
  524. * **Note:** default mapping callback is provided with `low` priority setting and does not cancel the event, so it is possible to
  525. * attach a custom callback after default callback and also use `data.viewPosition` calculated by default callback
  526. * (for example to fix it).
  527. *
  528. * **Note:** default mapping callback will not fire if `data.viewPosition` is already set.
  529. *
  530. * **Note:** these callbacks are called **very often**. For efficiency reasons, it is advised to use them only when position
  531. * mapping between given model and view elements is unsolvable using just elements mapping and default algorithm. Also,
  532. * the condition that checks if special case scenario happened should be as simple as possible.
  533. *
  534. * @event modelToViewPosition
  535. * @param {Object} data Data pipeline object that can store and pass data between callbacks. The callback should add
  536. * `viewPosition` value to that object with calculated {@link module:engine/view/position~Position view position}.
  537. * @param {module:engine/conversion/mapper~Mapper} data.mapper Mapper instance that fired the event.
  538. */
  539. /**
  540. * Fired for each view-to-model position mapping request. See {@link module:engine/conversion/mapper~Mapper#event:modelToViewPosition}.
  541. *
  542. * // See example in `modelToViewPosition` event description.
  543. * // This custom mapping will map positions from <span> element next to <img> to the "captionedImage" element.
  544. * mapper.on( 'viewToModelPosition', ( evt, data ) => {
  545. * const positionParent = viewPosition.parent;
  546. *
  547. * if ( positionParent.hasClass( 'image-caption' ) ) {
  548. * const viewImg = positionParent.previousSibling;
  549. * const modelImg = data.mapper.toModelElement( viewImg );
  550. *
  551. * data.modelPosition = new ModelPosition( modelImg, viewPosition.offset );
  552. * evt.stop();
  553. * }
  554. * } );
  555. *
  556. * **Note:** default mapping callback is provided with `low` priority setting and does not cancel the event, so it is possible to
  557. * attach a custom callback after default callback and also use `data.modelPosition` calculated by default callback
  558. * (for example to fix it).
  559. *
  560. * **Note:** default mapping callback will not fire if `data.modelPosition` is already set.
  561. *
  562. * **Note:** these callbacks are called **very often**. For efficiency reasons, it is advised to use them only when position
  563. * mapping between given model and view elements is unsolvable using just elements mapping and default algorithm. Also,
  564. * the condition that checks if special case scenario happened should be as simple as possible.
  565. *
  566. * @event viewToModelPosition
  567. * @param {Object} data Data pipeline object that can store and pass data between callbacks. The callback should add
  568. * `modelPosition` value to that object with calculated {@link module:engine/model/position~Position model position}.
  569. * @param {module:engine/conversion/mapper~Mapper} data.mapper Mapper instance that fired the event.
  570. */
  571. }
  572. mix( Mapper, EmitterMixin );