1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
|
/* global _, $ */
/**
*
* @copyright Copyright (c) 2018, Daniel Calviño Sánchez (danxuliu@gmail.com)
*
* @license GNU AGPL version 3 or any later version
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License as
* published by the Free Software Foundation, either version 3 of the
* License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*
*/
(function(_, $) {
'use strict';
OCA.SpreedMe = OCA.SpreedMe || {};
OCA.SpreedMe.Views = OCA.SpreedMe.Views || {};
/**
* Virtual list of DOM elements.
*
* The virtual list makes possible to create a list with an "unlimited"*
* number of elements. Despite the browser optimizations there is a limit in
* the number of elements that can be added to a document before the browser
* becomes sluggish when the document is further modified (due to having to
* layout/reflow a high number of elements); the virtual list solves that by
* keeping in the document only those elements that are currently visible,
* and refreshing them as needed when the list is scrolled.
*
* *The actual limit depends, among other things, on the maximum height for
* an element supported by the browser, the available memory to hold the
* elements, and the performance traversing linked lists, although it should
* be high enough for most common uses.
*
* The virtual list receives the container of the list (the element that the
* list elements would have been appended to if the virtual list was not
* used) in its constructor.
*
* The CSS style of the container must have a "visible" or (preferred) an
* "auto" value for its "overflow-y" property. Similarly, the positioning of
* the ".wrapper-background" and ".wrapper" elements child of the container
* must be set to "absolute".
*
* Elements are appended to the virtual list by first notifying the list
* that elements are going to be appended, then appending the elements, and
* finally processing the appended elements. Thus, even if there is only one
* element to add, first "appendElementStart()" must be called, followed by
* one or more calls to "appendElement()" each one with a single element,
* and followed by a final call to "appendElementEnd()". Elements are
* prepended in a similar way using the equivalent methods.
*
* The elements in the list can have different heights, and they can
* partially overlap their previous or next element due to the use of a
* negative top margin, but their top position must not exceed the top
* position of its previous element, and their bottom position must not
* exceed the bottom position of its next element.
*
* It is assumed that the position and size of an element will not change
* once added to the list. Changing the size of the container could change
* the position and size of all the elements, so in that case "reload()"
* needs to be called.
*
*
*
* Internal description:
* ---------------------
*
* Feast your eyes on this glorious ASCII art representation of the virtual
* list:
*
* ············· - List start / Wrapper background start - Top position = 0
* · ·
* · _ _ _ · _ First loaded element
* · ·
* · _ _ _ _ _ · _ Wrapper start - Top position ~= scroll position
* :___________: _
* | ~~~ | | Viewport start / Container top
* | ~~ |||
* | ~~ |||
* | ~~~~~ | | Viewport end / Container bottom
* :¯¯¯¯¯¯¯¯¯¯¯: ¯
* · ¯ ¯ ¯ ¯ ¯ · ¯ Wrapper end
* · ·
* · ·
* · ¯ ¯ ¯ · ¯ Last loaded element
* · ·
* · ·
* · ·
* · ·
* ············· - List end / Wrapper background end
*
* When the children of an element are larger than its parent and the parent
* can not grow any further the parent becomes a viewport for its children:
* it can only show a partial area of the children, but it provides an
* scroll bar to move the viewport up and down.
*
* The virtual list is based on that behaviour. In order to reduce the
* elements in the document, when the virtual list is set for a container,
* only those children of the container that are currently visible in the
* viewport are actually in the document; whenever the container is scrolled
* the elements are added and removed as needed.
*
* Specifically, the visible elements are added to and removed from a direct
* child of the container, a wrapper that only holds the visible elements.
*
* Besides the wrapper, the container has another direct children, a
* background element that simulates the full length of the list; although
* the background is empty its height is set to the height of all the
* elements in the list, so when the list is longer than the container the
* background causes the scroll bar to appear in the container as if it
* contained the real list.
*
* Both the background and the wrapper have an absolute position; this
* absolute position makes possible for the wrapper to move freely over the
* background, and also limits the layout calculations only to the wrapper
* itself when adding and removing the visible elements (although for better
* performance the updates are also done off-line, that is, with the wrapper
* detached from the document so only two reflows, one when it is detached
* and one when it is attached again, are done no matter the number of
* updated elements).
*
* Whenever the container is scrolled the elements are updated in the
* wrapper as needed; the top position of the wrapper is set so its elements
* are at the same distance from the top of the background as they would be
* if all their previous elements were in the document.
*
* In order to know where the elements should be in the full list as well as
* whether they are visible or not their position and size must have been
* calculated before. Thus, when elements are added to the virtual list they
* are briefly added to the document in a temporal wrapper; the position of
* this temporal wrapper is set based on the already added elements, so the
* browser can layout the new elements and their real position and size can
* be cached.
*
* Reloading the list recalculates the position and size of all the
* elements. When the list contains a lot of elements it is not possible to
* recalculate the values for all the elements at once, so they are first
* recalculated for the visible elements and then they are progressively
* recalculated for the rest of elements. During that process it is possible
* to scroll only to the already loaded elements (although eventually all
* the elements will be loaded and it will be possible to scroll again to
* any element).
*/
var VirtualList = function($container) {
this._$container = $container;
this._$firstElement = null;
this._$lastElement = null;
this._$firstLoadedElement = null;
this._$lastLoadedElement = null;
this._$firstVisibleElement = null;
this._$lastVisibleElement = null;
this._$wrapperBackground = $('<div class="wrapper-background"></div>');
this._$wrapperBackground.height(0);
this._$wrapper = $('<div class="wrapper"></div>');
this._$wrapper._top = 0;
this._$container.append(this._$wrapperBackground);
this._$container.append(this._$wrapper);
var self = this;
this._$container.on('scroll', function() {
self.updateVisibleElements();
});
};
VirtualList.prototype = {
getFirstElement: function() {
return this._$firstElement;
},
getFirstVisibleElement: function() {
return this._$firstVisibleElement;
},
getLastElement: function() {
return this._$lastElement;
},
getLastVisibleElement: function() {
return this._$lastVisibleElement;
},
prependElementStart: function() {
this._prependedElementsBuffer = document.createDocumentFragment();
delete this._$firstPrependedElement;
delete this._$lastPrependedElement;
},
appendElementStart: function() {
this._appendedElementsBuffer = document.createDocumentFragment();
delete this._$firstAppendedElement;
delete this._$lastAppendedElement;
},
prependElement: function($element) {
// ParentNode.prepend() is not compatible with older browsers.
this._prependedElementsBuffer.insertBefore($element.get(0), this._prependedElementsBuffer.firstChild);
if (this._$firstElement) {
this._$firstElement._previous = $element;
}
$element._next = this._$firstElement;
$element._previous = null;
this._$firstElement = $element;
if (!this._$lastElement) {
this._$lastElement = $element;
}
if (!this._$firstPrependedElement) {
this._$firstPrependedElement = $element;
}
this._$lastPrependedElement = $element;
},
appendElement: function($element) {
// ParentNode.append() is not compatible with older browsers.
this._appendedElementsBuffer.appendChild($element.get(0));
if (this._$lastElement) {
this._$lastElement._next = $element;
}
$element._previous = this._$lastElement;
$element._next = null;
this._$lastElement = $element;
if (!this._$firstElement) {
this._$firstElement = $element;
}
if (!this._$firstAppendedElement) {
this._$firstAppendedElement = $element;
}
this._$lastAppendedElement = $element;
},
prependElementEnd: function() {
// If the prepended elements are not immediately before the first
// loaded element there is nothing to load now; they will be loaded
// as needed with the other pending elements.
if (this._$firstPrependedElement._next !== this._$firstLoadedElement) {
delete this._prependedElementsBuffer;
return;
}
if (this._lastContainerWidth !== this._$container.width()) {
delete this._prependedElementsBuffer;
this.reload();
return;
}
this._loadPreviousElements(
this._$firstPrependedElement,
this._$lastPrependedElement,
this._prependedElementsBuffer
);
delete this._prependedElementsBuffer;
this.updateVisibleElements();
},
appendElementEnd: function() {
// If the appended elements are not immediately after the last
// loaded element there is nothing to load now; they will be loaded
// as needed with the other pending elements.
if (this._$firstAppendedElement._previous !== this._$lastLoadedElement) {
delete this._appendedElementsBuffer;
return;
}
if (this._lastContainerWidth !== this._$container.width()) {
delete this._appendedElementsBuffer;
this.reload();
return;
}
this._loadNextElements(
this._$firstAppendedElement,
this._$lastAppendedElement,
this._appendedElementsBuffer
);
delete this._appendedElementsBuffer;
this.updateVisibleElements();
},
/**
* Reloads the list to adjust to the new size of the container.
*
* This needs to be called whenever the size of the container has
* changed.
*
* When the width of the container has changed it is not possible to
* guarantee that exactly the same elements that were visible before
* will be visible after the list is reloaded. Due to this, in those
* cases reloading the list just ensures that the last element that was
* partially visible before will be fully visible after the list is
* reloaded.
*
* On the other hand, when only the height has changed no reload is
* needed; in that case the visibility of the elements is updated based
* on the new height.
*
* Reloading the list requires to recalculate the position and size of
* all the elements. The initial call reloads the last visible element
* (if any) and some of its previous and next siblings; the rest of the
* elements will be queued to be progressively updated until all are
* loaded. During this process it is possible to scroll only to those
* elements already loaded, although further elements can be appended or
* prepended if needed and they will be available once the reload ends.
*
* In browsers with subpixel accuracy for the position and size that use
* integer values for the scroll position, like Firefox, reloading the
* list causes a wiggly effect (and, in some cases, a slight drift) due
* to prepending the elements and trying to keep the scroll position, as
* the scroll position is rounded to an int but the position of the
* elements is a float.
*/
reload: function() {
if (this._lastContainerWidth === this._$container.width()) {
// If the width is the same the cache is still valid, so no need
// for a full reload.
this.updateVisibleElements();
return;
}
if (this._pendingLoad) {
clearTimeout(this._pendingLoad);
delete this._pendingLoad;
}
this._lastContainerWidth = this._$container.width();
var $initialElement = this._$lastVisibleElement;
if (!$initialElement) {
// No element was visible; either the list was reloaded when
// empty or during the first append/prepend of elements.
$initialElement = this._$lastElement;
}
if (!$initialElement) {
// The list is empty, so there is nothing to load.
return;
}
// Detach all the visible elements from the wrapper
this._$wrapper.detach();
while (this._$firstVisibleElement && this._$firstVisibleElement !== this._$lastVisibleElement._next) {
this._$firstVisibleElement.detach();
this._$firstVisibleElement = this._$firstVisibleElement._next;
}
this._$firstVisibleElement = null;
this._$lastVisibleElement = null;
this._$wrapper._top = 0;
this._$wrapper.css('top', this._$wrapper._top);
this._$wrapper.appendTo(this._$container);
// Reset wrapper background
this._$wrapperBackground.height(0);
this._loadInitialElements($initialElement);
// Scroll to the last visible element, or to the top of the next one
// to prevent it from becoming the last visible element when the
// visibilities are updated.
if ($initialElement._next) {
// The implicit "Math.floor()" on the scroll position when the
// browser has subpixel accuracy but uses int positions for
// scrolling ensures that the next element to the last visible
// one will not become visible (which could happen if the value
// was rounded instead).
this._$container.scrollTop($initialElement._next._top - this._getElementOuterHeightWithoutMargins(this._$container));
} else {
// As the last visible element is also the last element this
// simply scrolls the list to the bottom.
this._$container.scrollTop($initialElement._top + $initialElement._height);
}
this.updateVisibleElements();
this._queueLoadOfPendingElements();
},
_loadInitialElements: function($initialElement) {
var $firstElement = $initialElement;
var $lastElement = $firstElement;
var elementsBuffer = document.createDocumentFragment();
var $currentElement = $firstElement;
var i;
for (i = 0; i < 50 && $currentElement; i++) {
// ParentNode.prepend() is not compatible with older browsers.
elementsBuffer.insertBefore($currentElement.get(0), elementsBuffer.firstChild);
$lastElement = $currentElement;
$currentElement = $currentElement._previous;
}
$currentElement = $firstElement._next;
for (i = 0; i < 50 && $currentElement; i++) {
// ParentNode.append() is not compatible with older browsers.
elementsBuffer.appendChild($currentElement.get(0));
$firstElement = $currentElement;
$currentElement = $currentElement._next;
}
this._$firstLoadedElement = null;
this._$lastLoadedElement = null;
this._loadPreviousElements(
$firstElement,
$lastElement,
elementsBuffer
);
// FIXME it is happily assumed that the initial load covers the full
// view with 50 and 50 elements before and after... but it should be
// actually verified and enforced loading again other elements as
// needed.
},
_queueLoadOfPendingElements: function() {
if (this._pendingLoad) {
return;
}
// To load the elements they need to be rendered again, so it is a
// rather costly operation. A small interval between loads, even
// with just a few elements, could hog the browser and cause its UI
// to become unresponsive, so a "long" interval is used instead; to
// compensate for the "long" interval the number of elements loaded
// in each batch is rather large, but still within a reasonable
// limit that should be renderable by the browser without causing
// (much :-) ) jank.
this._pendingLoad = setTimeout(function() {
delete this._pendingLoad;
var numberOfElementsToLoad = 200;
numberOfElementsToLoad -= this._loadPreviousPendingElements(numberOfElementsToLoad/2);
this._loadNextPendingElements(numberOfElementsToLoad);
// The loaded elements are out of view (it is assumed that the
// initial load of elements cover the full visible area), so no
// need to update the visible elements.
}.bind(this), 100);
},
_loadPreviousPendingElements: function(numberOfElementsToLoad) {
if (!this._$firstLoadedElement || this._$firstLoadedElement === this._$firstElement) {
return 0;
}
var prependedElementsBuffer = document.createDocumentFragment();
var $firstPrependedElement = this._$firstLoadedElement._previous;
var $lastPrependedElement = $firstPrependedElement;
var $currentElement = $firstPrependedElement;
var i;
for (i = 0; i < numberOfElementsToLoad && $currentElement; i++) {
// ParentNode.prepend() is not compatible with older browsers.
prependedElementsBuffer.insertBefore($currentElement.get(0), prependedElementsBuffer.firstChild);
$lastPrependedElement = $currentElement;
$currentElement = $currentElement._previous;
}
this._loadPreviousElements(
$firstPrependedElement,
$lastPrependedElement,
prependedElementsBuffer
);
this._queueLoadOfPendingElements();
return i;
},
_loadNextPendingElements: function(numberOfElementsToLoad) {
if (!this._$lastLoadedElement || this._$lastLoadedElement === this._$lastElement) {
return 0;
}
var appendedElementsBuffer = document.createDocumentFragment();
var $firstAppendedElement = this._$lastLoadedElement._next;
var $lastAppendedElement = $firstAppendedElement;
var $currentElement = $firstAppendedElement;
var i;
for (i = 0; i < numberOfElementsToLoad && $currentElement; i++) {
// ParentNode.append() is not compatible with older browsers.
appendedElementsBuffer.appendChild($currentElement.get(0));
$lastAppendedElement = $currentElement;
$currentElement = $currentElement._next;
}
this._loadNextElements(
$firstAppendedElement,
$lastAppendedElement,
appendedElementsBuffer
);
this._queueLoadOfPendingElements();
return i;
},
_loadPreviousElements: function($firstElementToLoad, $lastElementToLoad, elementsBuffer) {
var $wrapper = $('<div class="wrapper"></div>');
$wrapper._top = 0;
var $firstExistingElement = $firstElementToLoad._next;
if ($firstExistingElement) {
// The wrapper is already at the top, so no need to set its
// position.
// Include the next element, as its position may change due to
// collapsing margins.
$wrapper.append($firstExistingElement.clone());
}
this._$container.append($wrapper);
var previousWrapperHeight = this._getElementHeight($wrapper);
$wrapper.prepend(elementsBuffer);
var wrapperHeightDifference = this._getElementHeight($wrapper) - previousWrapperHeight;
// Although getting the height with jQuery < 3.X rounds to the
// nearest integer setting the height respects the given float
// number.
this._$wrapperBackground.height(this._getElementHeight(this._$wrapperBackground) + wrapperHeightDifference);
// Note that the order of "first/last" is not the same for the main
// elements and the elements passed to this method.
if (!this._$lastLoadedElement) {
this._$lastLoadedElement = $firstElementToLoad;
}
this._$firstLoadedElement = $lastElementToLoad;
while ($firstElementToLoad !== $lastElementToLoad._previous) {
this._updateCache($firstElementToLoad, $wrapper);
$firstElementToLoad = $firstElementToLoad._previous;
}
// Remove the temporal wrapper used to layout and get the height of
// the added items.
$wrapper.detach();
$wrapper.children().detach();
$wrapper.remove();
// Update the cached position of elements after the prepended ones.
while ($firstExistingElement !== this._$lastLoadedElement._next) {
$firstExistingElement._top += wrapperHeightDifference;
$firstExistingElement._topRaw += wrapperHeightDifference;
$firstExistingElement = $firstExistingElement._next;
}
// Keep the scrolling at the same point as before the elements were
// prepended.
// Despite having subpixel accuracy for positions and sizes, Firefox
// uses integer values for the scroll position, so the proper scroll
// position would be implicitly truncated. Instead, the scroll
// position is explicitly rounded to mitigate a progressive "drift"
// when several batches of elements are prepended.
// Note, however, that rounded the value just mitigates, but does
// not fully prevent the drift, and when several batches are
// prepended in a row in a short period of time the result is a
// wiggly effect in the existing elements due to the successive
// corrections in the scroll positions.
// Besides that, the drawback of this approach is that the scrolling
// in browsers with subpixel accuracy and float values for the
// scroll position (maybe Firefox mobile?) will not be as accurate
// as it could be.
this._$container.scrollTop(Math.round(this._$container.scrollTop() + wrapperHeightDifference));
// Update the position of the wrapper with the visible elements.
// This is needed even if "updateVisibleElements()" is called later,
// as it could "short circuit" before reaching the point where the
// wrapper position is updated.
if (this._$firstVisibleElement) {
this._$wrapper._top += wrapperHeightDifference;
this._$wrapper.css('top', this._$wrapper._top);
}
},
_loadNextElements: function($firstElementToLoad, $lastElementToLoad, elementsBuffer) {
var $wrapper = $('<div class="wrapper"></div>');
$wrapper._top = 0;
if ($firstElementToLoad._previous) {
$wrapper.css('top', $firstElementToLoad._previous._topRaw);
$wrapper._top = $firstElementToLoad._previous._topRaw;
// Include the previous element, as it may change the
// position of the newest element due to collapsing margins
$wrapper.append($firstElementToLoad._previous.clone());
}
this._$container.append($wrapper);
var previousWrapperHeight = this._getElementHeight($wrapper);
$wrapper.append(elementsBuffer);
var wrapperHeightDifference = this._getElementHeight($wrapper) - previousWrapperHeight;
// Although getting the height with jQuery < 3.X rounds to the
// nearest integer setting the height respects the given float
// number.
this._$wrapperBackground.height(this._getElementHeight(this._$wrapperBackground) + wrapperHeightDifference);
if (!this._$firstLoadedElement) {
this._$firstLoadedElement = $firstElementToLoad;
}
this._$lastLoadedElement = $lastElementToLoad;
while ($firstElementToLoad !== $lastElementToLoad._next) {
this._updateCache($firstElementToLoad, $wrapper);
$firstElementToLoad = $firstElementToLoad._next;
}
// Remove the temporal wrapper used to layout and get the height of
// the added items.
$wrapper.detach();
$wrapper.children().detach();
$wrapper.remove();
},
/**
* Updates the cached position and size of the given element.
*
* The element must be a child of a wrapper currently in the container
* (although it can be a temporal wrapper, it does not need to be the
* main one); detached elements can not be used, as the values to cache
* would be invalid in that case.
*
* The element top position is relative to the wrapper, and the wrapper
* top position plus the element top position is expected to place the
* element at the proper offset from the top of the container.
*
* @param {jQuery} $element the element to update its cache.
* @param {jQuery} $wrapper the parent wrapper of the element.
*/
_updateCache: function($element, $wrapper) {
$element._height = this._getElementOuterHeight($element);
// The top position of an element must be got from the element
// itself; it can not be based on the top position and height of the
// previous element, because the browser may merge/collapse the
// margins.
$element._top = $wrapper._top + this._getElementTopPosition($element);
$element._topRaw = $element._top;
var marginTop = parseFloat($element.css('margin-top'));
if (marginTop < 0) {
$element._topRaw -= marginTop;
}
},
/**
* Returns the top position, from the top margin, of the given element.
*
* The returned value takes into account a negative top margin, which
* pulls up the element closer to the previous element.
*
* @param jQuery $element the jQuery element to get its height.
*/
_getElementTopPosition: function($element) {
// When the margin is positive, jQuery returns the proper top
// position of the element (that is, including the top margin).
// However, when it is negative, jQuery returns where the top
// position of the element would be if there was no margin, so in
// those cases the top position returned by jQuery is below the
// actual top position of the element.
var marginTop = parseFloat($element.css('margin-top'));
if (marginTop >= 0) {
return $element.position().top;
}
return $element.position().top + marginTop;
},
/**
* Returns the height of the given element.
*
* This must be used instead of jQuery.height(); before the 3.0.0
* release jQuery rounded the height to the nearest integer, but Firefox
* has subpixel accuracy, so the height returned by jQuery can not be
* used in the calculations.
*
* @param jQuery $element the jQuery element to get its height.
*/
_getElementHeight: function($element) {
return $element.get(0).getBoundingClientRect().height;
},
/**
* Returns the outer height, without margins, of the given element.
*
* The returned value includes the height, the padding and the border.
*
* This must be used instead of jQuery.height(); before the 3.0.0
* release jQuery rounded the height to the nearest integer, but Firefox
* has subpixel accuracy, so the height returned by jQuery can not be
* used in the calculations.
*
* @param jQuery $element the jQuery element to get its height.
*/
_getElementOuterHeightWithoutMargins: function($element) {
// Although before jQuery 3.0.0 the height is rounded to the nearest
// integer the padding and border width, on the other hand, are
// returned as a float value as expected.
var paddingTop = parseFloat($element.css('padding-top'));
var paddingBottom = parseFloat($element.css('padding-bottom'));
var borderTop = parseFloat($element.css('border-top-width'));
var borderBottom = parseFloat($element.css('border-bottom-width'));
return this._getElementHeight($element) + paddingTop + paddingBottom + borderTop + borderBottom;
},
/**
* Returns the full outer height, with margins, of the given element.
*
* The returned value includes the height, the padding, the border and
* the margin; negative margins are not taken into account, as they do
* not affect the visible height of the element; they only pull up the
* element (negative top margin) or its next element (negative bottom
* margin), but without modifying its visible height.
*
* This must be used instead of jQuery.height(); before the 3.0.0
* release jQuery rounded the height to the nearest integer, but Firefox
* has subpixel accuracy, so the height returned by jQuery can not be
* used in the calculations.
*
* @param jQuery $element the jQuery element to get its height.
*/
_getElementOuterHeight: function($element) {
// Although before jQuery 3.0.0 the height is rounded to the nearest
// integer the margin, on the other hand, is returned as a float
// value as expected.
// Besides that note that outerHeight(true) would return a smaller
// height than the actual height when there are negative margins, as
// in that case jQuery would substract the negative margin from the
// overall height of the element.
var marginTop = Math.max(0, parseFloat($element.css('margin-top')));
var marginBottom = Math.max(0, parseFloat($element.css('margin-bottom')));
return this._getElementOuterHeightWithoutMargins($element) + marginTop + marginBottom;
},
/**
* Updates the visible elements.
*
* Elements no longer in the viewport are removed, while elements now in
* the viewport are added.
*
* Note that the float precision problems are not handled in the
* visibility checks, so in browsers with subpixel accuracy, like
* Firefox, elements in which their bottom is very very close to the top
* of the container, or elements in which their top is very very close
* to the bottom of the container may be shown or hidden when they
* should not. However, this should not be a problem, as only fractions
* of a pixel would be wrongly shown or hidden.
*/
updateVisibleElements: function() {
if (!this._$firstVisibleElement && !this._$firstLoadedElement) {
return;
}
if (!this._$firstVisibleElement) {
this._$firstVisibleElement = this._$firstLoadedElement;
this._$lastVisibleElement = this._$firstVisibleElement;
this._$wrapper.append(this._$firstVisibleElement);
}
var visibleAreaTop = this._$container.scrollTop();
var visibleAreaBottom = visibleAreaTop + this._getElementOuterHeightWithoutMargins(this._$container);
var firstVisibleElementIsStillPartiallyVisible =
this._$firstVisibleElement._top <= visibleAreaTop &&
this._$firstVisibleElement._top + this._$firstVisibleElement._height > visibleAreaTop;
var lastVisibleElementIsStillPartiallyVisible =
this._$lastVisibleElement._top < visibleAreaBottom &&
this._$lastVisibleElement._top + this._$lastVisibleElement._height >= visibleAreaBottom;
// The first element could be being pulled up into its previous
// element due to a negative top margin, so it is necessary to
// ensure that the previous element is not visible even if the first
// one "crosses" the top of the visible area.
var previousElementToFirstVisibleElementIsNotVisibleYet =
!this._$firstVisibleElement._previous ||
this._$firstVisibleElement._previous._top + this._$firstVisibleElement._previous._height <= visibleAreaTop;
// The next element could be pulled up into the last visible element
// due to a negative top margin, so it is necessary to ensure that
// it is not visible even if the last one "crosses" the bottom of
// the visible area.
var nextElementToLastVisibleElementIsNotVisibleYet =
!this._$lastVisibleElement._next ||
this._$lastVisibleElement._next._top >= visibleAreaBottom;
if (firstVisibleElementIsStillPartiallyVisible &&
lastVisibleElementIsStillPartiallyVisible &&
previousElementToFirstVisibleElementIsNotVisibleYet &&
nextElementToLastVisibleElementIsNotVisibleYet) {
return;
} else {
this._$wrapper.detach();
}
// The currently visible area does not contain any of the visible
// elements.
if (this._$firstVisibleElement._top >= visibleAreaBottom ||
this._$lastVisibleElement._top + this._$lastVisibleElement._height <= visibleAreaTop) {
// Remove all visible elements.
while (this._$firstVisibleElement !== this._$lastVisibleElement._next) {
this._$firstVisibleElement.detach();
this._$firstVisibleElement = this._$firstVisibleElement._next;
}
// Show the new first visible element.
this._$firstVisibleElement = this._$firstLoadedElement;
while (this._$firstVisibleElement._top + this._$firstVisibleElement._height <= visibleAreaTop) {
this._$firstVisibleElement = this._$firstVisibleElement._next;
}
this._$firstVisibleElement.prependTo(this._$wrapper);
this._$lastVisibleElement = this._$firstVisibleElement;
}
// Remove leading elements no longer visible.
while (this._$firstVisibleElement._top + this._$firstVisibleElement._height <= visibleAreaTop) {
this._$firstVisibleElement.detach();
this._$firstVisibleElement = this._$firstVisibleElement._next;
}
// Prepend leading elements now visible.
while (this._$firstVisibleElement._previous &&
this._$firstVisibleElement._previous !== this._$firstLoadedElement._previous &&
this._$firstVisibleElement._previous._top + this._$firstVisibleElement._previous._height > visibleAreaTop) {
this._$firstVisibleElement._previous.prependTo(this._$wrapper);
this._$firstVisibleElement = this._$firstVisibleElement._previous;
}
// Align wrapper with the top raw position (without negative
// margins) of the first visible element.
this._$wrapper._top = this._$firstVisibleElement._topRaw;
this._$wrapper.css('top', this._$wrapper._top);
// Remove trailing elements no longer visible.
while (this._$lastVisibleElement._top >= visibleAreaBottom) {
this._$lastVisibleElement.detach();
this._$lastVisibleElement = this._$lastVisibleElement._previous;
}
// Append trailing elements now visible.
while (this._$lastVisibleElement._next &&
this._$lastVisibleElement._next !== this._$lastLoadedElement._next &&
this._$lastVisibleElement._next._top < visibleAreaBottom) {
this._$lastVisibleElement._next.appendTo(this._$wrapper);
this._$lastVisibleElement = this._$lastVisibleElement._next;
}
this._$wrapper.appendTo(this._$container);
},
/**
* Scroll the list to the given element.
*
* The element will be aligned with the top of the list (or as far as
* possible, in case the element is at the bottom).
*
* @param {jQuery} $element the element of the list to scroll to.
*/
scrollTo: function($element) {
if (!this._isLoaded($element)) {
return;
}
this._$container.scrollTop($element._top);
// The visible elements are updated when the scroll event is
// handled. However, as the scroll event is asynchronous, it is not
// guaranteed that it will be handled before this method returns; as
// the caller could expect that the visibility of elements is
// updated when scrolling programatically this must be explicitly
// done.
// Note that, although the event is handled asynchronously (and in
// some cases several scrolls can be merged in a single event) the
// value returned by scrollTop() is always the expected one
// immediately after setting it with scrollTop(value).
this.updateVisibleElements();
},
/**
* Returns whether the given element is loaded or not.
*
* @param {jQuery} $element the element to check.
* @return true if the element is loaded, false otherwise.
*/
_isLoaded: function($element) {
if (!this._$firstLoadedElement || !this._$lastLoadedElement) {
return false;
}
var $currentElement = this._$firstLoadedElement;
while ($currentElement !== this._$lastLoadedElement._next) {
if ($currentElement === $element) {
return true;
}
$currentElement = $currentElement._next;
}
return false;
},
};
OCA.SpreedMe.Views.VirtualList = VirtualList;
})(_, $);
|