-
Notifications
You must be signed in to change notification settings - Fork 791
Expand file tree
/
Copy pathOverview.src.html
More file actions
420 lines (348 loc) · 17.4 KB
/
Overview.src.html
File metadata and controls
420 lines (348 loc) · 17.4 KB
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
<h1>CSS Scroll Snap Points Module Level 1</h1>
<pre class='metadata'>
Group: csswg
Shortname: css-snappoints
Level: 1
Status: ED
ED: http://dev.w3.org/csswg/css-snappoints/
Editor: Matt Rakow, Microsoft
Editor: Jacob Rossi, Microsoft
Abstract: This module contains features to control panning and scrolling behavior with "snap points".
!Issue Tracking: <a href="http://wiki.csswg.org/spec/css-snappoints">http://wiki.csswg.org/spec/css-snappoints</a>
Ignored Terms: scroll-snap-points-*
</pre>
<h2 id="intro">Introduction</h2>
<em>This section is not normative.</em>
Popular UX paradigms for scrollable content frequently employ paging through content,
or sectioning into logical divisions.
This is especially true for touch interactions
where it is quicker and easier for users to quickly pan through a flatly-arranged breadth of content
rather than delving into a heirarchical structure through tap navigation.
For example, it is easier for a user to view many photos in a photo album
by panning through a photo slideshow view
rather than tapping on individual photos in an album.
However, given the imprecise nature of scrolling inputs
like touch panning and mousewheel scrolling,
it is difficult for web developers to guarantee a well-controlled scrolling experience,
in particular creating the effect of paging through content.
For instance, it is easy for a user to land at an awkward scroll offset
which leaves a page partially on-screen when panning.
To this end, we introduce scroll snap points
which enforce the scroll offsets that a scroll container may end at
after a scrolling operation has completed.
<h3 id="placement">Module interactions</h3>
This module extends the scrolling user interface features defined in [[!CSS21]] section 11.1.
None of the properties in this module apply to the ''::first-line'' and ''::first-letter'' pseudo-elements.
<h3 id="values">Values</h3>
This specification follows the
<a href="http://www.w3.org/TR/CSS21/about.html#property-defs">CSS property
definition conventions</a> from [[!CSS21]]. Value types not defined in
this specification are defined in CSS Level 2 Revision 1 [[!CSS21]].
Other CSS modules may expand the definitions of these value types: for
example [[CSS3VAL]], when combined with this module, expands the
definition of the <<length>> value type as used in this specification.
<h2 id="examples">Motivating Examples</h2>
<div class="example">
In this example, a series of images arranged in a <a>scroll container</a>
are used to build a photo gallery.
The <a>scroll container</a> is sized to the same size of the images contained therein.
Using mandatory snap points,
scrolling will always complete with a snap point aligned to the edge of the <a>scroll container</a>.
By aligning a snap point at the edge of each image,
this creates a photo viewer were users can scroll through the images one at a time.
<pre>
img {
width:500px;
}
.photoGallery {
width: 500px;
overflow-x: auto;
overflow-y: hidden;
white-space: nowrap;
/* Sets up points to which scrolling
will snap along x-axis */
scroll-snap-points-x: repeat(100%);
/* Requires that scrolling always end at a snap point when
the operation completes (hard snap) */
scroll-snap-type: mandatory;
}
</pre>
<pre>
<div class="photoGallery">
<img src="img1.jpg">
<img src="img2.jpg">
<img src="img3.jpg">
<img src="img4.jpg">
<img src="img5.jpg">
</div>
</pre>
<figure>
<img src="interval_snap_points.png" alt="">
<figcaption>
The layout of the scroll container's contents in the example.
Snap points are set along the x-axis,
starting at 0px and repeating at intervals of 100% of the scroll container's width.
</figcaption>
</figure>
</div>
<div class="example">
This example also builds a photo gallery as in example 1. However, in this example the <a>scroll container</a>
is larger than the photos contained within (such that multiple images may be seen simultaneously), and the image
sizes vary (such that a repeating snap interval would not be effective). Using mandatory element-based snap
points, scrolling will always complete with an image centered in the <a>scroll container</a>.
<pre>
img {
/* Defines the center of each photo as the
coordinate that should be used for snapping */
scroll-snap-coordinate: 50% 50%;
}
.photoGallery {
width: 500px;
overflow-x: auto;
overflow-y: hidden;
white-space: nowrap;
/* Denotes that snap points will be defined
by the elements contained within. */
scroll-snap-points-x: elements;
/* Specifies that each element's snap coordinate should
align with the center of the scroll container */
scroll-snap-destination: 50% 50%;
/* Requires that scrolling always end at a snap point
when the operation completes (hard snap). */
scroll-snap-type: mandatory;
}
</pre>
<pre>
<div class="photoGallery">
<img src="img1.jpg">
<img src="img2.jpg">
<img src="img3.jpg">
<img src="img4.jpg">
<img src="img5.jpg">
</div>
</pre>
<figure>
<img src="element_snap_points.png" alt="">
<figcaption>
The layout of the scroll container's contents in the example.
The snap-destination is horizontally and vertically centered within the scroll container
(represented by a red X),
and each element has its snap coordinate horizontally and vertically centered within the element
(represented by yellow plus signs).
</figcaption>
</figure>
</div>
<div class="example">
This example builds a paginated document that aligns each page near to (but not exactly on) the edge of the <a>scroll container</a>.
This allows the previous page to "peek" in from above in order to make the user aware that they are not yet at the top of the document.
Using proximity snap points instead of mandatory snap points allows the user to stop halfway through a page (rather than forcing them
to snap one page at a time). However, if a scrolling operation would finish near a snap point, then the scroll will be adjusted to
align the page as specified.
<pre>
.page {
/* Defines the top center of each page as the
coordinate that should be used for snapping */
scroll-snap-coordinate: 50% 0;
}
.docScroller {
width: 500px;
overflow-x: hidden;
overflow-y: auto;
/* Denotes that snap points will be defined
by the elements contained within. */
scroll-snap-points-y: elements;
/* Specifies that each element's snap coordinate should
align with the center of the scroll container, offset
a short distance from the top edge. */
scroll-snap-destination: 50% 100px;
/* Encourages scrolling to end at a snap point when the
operation completes, if it is near a snap point */
scroll-snap-type: proximity;
}
</pre>
<pre>
<div class="docScroller">
<div class="page">Page 1</div>
<div class="page">Page 2</div>
<div class="page">Page 3</div>
<div class="page">Page 4</div>
</div>
</pre>
<figure>
<img src="element_snap_points_offset.png" alt="">
<figcaption>
The layout of the scroll container's contents in the example.
The snap-destination is horizontally centered and offset 100px from the top edge with respect to the scroll container
(represented by a red X),
and each element has its snap coordinate horizontally centered and top-aligned with respect to the element
(represented by yellow plus signs).
</figcaption>
</figure>
</div>
<h2 id="definitions">Definitions</h2>
<dl>
<dt><dfn export>scroll container</dfn>
<dd>
An element which provides a scrolling user interface as described in [[!CSS21]], particularly in the section on overflow.
</dl>
<h2 id="scroll-snap-type">Scroll Snap Types: the 'scroll-snap-type' property</h2>
The ''scroll-snap-type'' property is used to define the physics characteristics of panning and scrolling, if any. It defines how and when snap points are enforced on the scroll container it is applied to.
<pre class='propdef'>
Name: scroll-snap-type
Value: none | mandatory | proximity
Initial: none
Applies to: <a>scroll containers</a>
Inherited: no
Percentages: n/a
Media: interactive
Computed value: specified value
Animatable: no
</pre>
<dl dfn-type="value" dfn-for="scroll-snap-type">
<dt><dfn>none</dfn>
<dd>
This <a>scroll container</a> must ignore snap points, if any, when scrolled.
<dt><dfn>mandatory</dfn>
<dd>
This <a>scroll container</a> must come to rest on a snap point at the termination of a scroll, if possible.
<dt><dfn>proximity</dfn>
<dd>
This <a>scroll container</a> may come to rest on a snap point at the termination of a scroll at the discretion of the UA given the parameters of the scroll.
</dl>
<p class="issue">
Could this be defined on a per-snap-point basis? What does it mean to mix types of snap points within a single scroller? Alternatively, should this be definable separately for each axis?
</p>
<p class="issue">
Need to consider the "snap-area" behavior described by fantasai. Maybe define this as repelling snap...lines? guardrails? bumpers? boundaries? limits? at the boundary?
</p>
<p class="issue">
If we do some behavior like snap-area, what happens when near an edge -- try to align with the edge or not?
</p>
<p class="issue">
What happens in zooming scenarios, e.g. if the images become larger than the viewport? Snapping makes less sense in this case. Is this addressable with a snap-area type of effect?
</p>
<p class="issue">
Consider naming conventions like in Grid Layout for grouping properties on the container vs. items.
</p>
<p class="issue">
Specify behavior of mandatory in a broader range of scenarios that induce scrolling or change content -- e.g. element is removed or moved. Does the scroller scroll to the nearest valid snap point?
</p>
<h2 id="scroll-snap-points">Scroll Snap Points: the 'scroll-snap-points-x' and 'scroll-snap-points-y' properties</h2>
The 'scroll-snap-points-x' and 'scroll-snap-points-y' properties
are used to define the positioning of snap points
within the content of the <a>scroll container</a> they are applied to,
or to declare the scroll container as snapping to elements.
<pre class="propdef">
Name: scroll-snap-points-x, scroll-snap-points-y
Value: [ <<length>># ,]? repeat(<<length>>) | <<length>># | elements
Initial: repeat(100%)
Applies to: <a>scroll containers</a>
Inherited: no
Percentages: relative to same axis of the padding-box of the <a>scroll container</a>
Media: interactive
Computed value: specified value, with lengths made absolute
Animatable: no
</pre>
<dl dfn-type="value" dfn-for="snap-points-x, snap-points-y">
<dt><dfn>[ <<length>># ,]? repeat(<<length>>)</dfn>
<dd>
Defines a list of starting snap points and an interval at which additional snap points are defined, starting from the final snap point of the list.
The first <<length>># list is the set of explicitly defined snap points, and the repeat(<<length>>) function defines the interval to repeat thereafter.
<dt><dfn><<length>>+</dfn>
<dd>
Defines one or more discrete snap points for the <a>scroll container</a>,
measured as lengths from the container's relevant <a>start</a> edge.
<dt><dfn>elements</dfn>
<dd>
Declares that the snap points for this scroll container
will be determined by the elements contained within.
In particular, by the combination of the element boxes' positions in layout
and their corresponding scroll-snap-coordinate properties,
in conjunction with this element's scroll-snap-destination property.
</dl>
<p class="issue">
With the split-axis approach, the list and interval can result in unexpected behavior in 2d scrollers. For example, if you only want two diagonally-positioned snap points at (x1, y1) and (x2, y2), you will instead get (x1, y1), (x1, y2), (x2, y1), and (x2, y2).
</p>
<p class="issue">
Is the "elements" value needed? Is it important to avoid mixing list/interval with element snap points?
</p>
<p class="issue">
If we do stick with a value like "elements", is there a better name for it (e.g. if we can snap to non-elements like fragments).
</p>
<p class="issue">
Express as position instead of length unit?
</p>
<p class="issue">
Is the list format required, if we have element snapping? If yes, need a scenario justification. If no, remove.
</p>
<h2 id="scroll-snap-destination">Scroll Snap Destination: the 'scroll-snap-destination' property</h2>
The 'scroll-snap-destination' property is used to define the x and y coordinate within the <a>scroll container</a>
which element snap points will align with
when the ''elements'' value is used for the 'scroll-snap-points-*' property.
<pre class="propdef">
Name: scroll-snap-destination
Value: <<length>>{2}
Initial: 0px
Applies to: <a>scroll containers</a>
Inherited: no
Percentages: relative to width and height of the padding-box of the <a>scroll container</a>
Media: interactive
Computed value: specified value, with lengths made absolute
Animatable: yes
</pre>
<dl dfn-type="value" dfn-for="scroll-snap-destination">
<dt><dfn><<length>>{2}</dfn>
<dd>
Specifies the offset of the snap destination from the leading edge of the scroll container. The first value gives the x coordinate of the snap destination, the second value its y coordinate.
</dl>
<p class="issue">
Clarify "leading edge" -- want this to respond appropriately to writing modes
</p>
<h2 id="scroll-snap-coordinate">Scroll Snap Coordinate: the 'scroll-snap-coordinate' property</h2>
The 'scroll-snap-coordinate' property is used to define the x and y coordinate within the element
which will align with the nearest ancestor <a>scroll container's</a> snap-destination
when the ''elements'' value is used for the 'scroll-snap-points-*' property
of the nearest ancestor <a>scroll container's</a> respective axis.
<p class="issue">
How does this work with fragmentation?
</p>
<p class="issue">
Consider alternative naming besides "coordinate".
</p>
<pre class="propdef">
Name: scroll-snap-coordinate
Value: none | <<length>>{2}#
Initial: none
Applies to: all elements
Inherited: no
Percentages: refer to the element box used by the box-sizing property
Media: interactive
Computed value: specified value, with lengths made absolute
Animatable: yes
</pre>
<dl dfn-type=value dfn-for="scroll-snap-coordinate">
<dt><dfn>none</dfn>
<dd>
Specifies that this element does not contribute a snap point.
<dt><dfn><<length>>{2}#</dfn>
<dd>
Specifies the offset of the snap coordinates from the leading edge of the element box used by the box-sizing property. For each pairing, the first value gives the x coordinate of the snap coordinate, the second value its y coordinate.
</dl>
<p class="issue">
Don't tie this to box-sizing.
</p>
<p class="issue">
Specify interaction with transforms.
</p>
<h2 id="CSSOM">CSSOM</h2>
<p class="issue">
Need to define how to read back points.
</p>
<p class="issue">
How to navigate directly to a snap point (e.g. with a hash or similar) -- e.g. enable direct linking to a specific page in a document
</p>
<p class="issue">
Supplementary APIs (e.g. snap-to-next, snap-to-previous, jump-to-N)
</p>
<h2 class=no-num id="acknowledgments">Acknowledgments</h2>
Many thanks to lots of people for their proposals and recommendations, some of which are incorporated into this document.