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Gecko:CSSScrollSnapping: Difference between revisions
→Proposal
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The algorithm for computing which snapping opportunity (if any) to take is gesture and UA dependent. However the following constraints must be honored: | The algorithm for computing which snapping opportunity (if any) to take is gesture and UA dependent. However the following constraints must be honored: | ||
* When scrolling along an axis for which 'scroll-snap-type' is 'mandatory', the UA | * If the scroll gesture has a definite direction (this is UA-dependent, but it includes clicking on scrollbar buttons or pressing up/down keys), the UA must not choose a snapping opportunity that makes the gesture result in scrolling in the opposite direction. | ||
* When scrolling along an axis for which 'scroll-snap-type' is 'mandatory', the UA must choose one of the snapping opportunities for that axis (if there are any valid opportunities, subject to the previous requirement). However this requirement is lifted if one or more of the snapping opportunities' boxes B is larger than the scroll-port. | |||
* When 'scroll-snap-type' is 'none' for some axis, no scroll snapping occurs along that axis. | * When 'scroll-snap-type' is 'none' for some axis, no scroll snapping occurs along that axis. | ||
UAs should apply scroll snapping to all user scroll gestures (including keyboard, scrollbars, etc). Script-driven scrolling (e.g. setting <tt>scrollLeft</tt> or <tt>scrollTop</tt>) is never affected by scroll snapping. Layout changes that affect the positions of elements with 'scroll-snap-edges', or dynamic changes to values of 'scroll-snap-edges', do not trigger snapping in the absence of a scroll gesture, even if 'mandatory' snapping is requested. | UAs should apply scroll snapping to all user scroll gestures (including keyboard, scrollbars, etc). Script-driven scrolling (e.g. setting <tt>scrollLeft</tt> or <tt>scrollTop</tt>) is never affected by scroll snapping. Layout changes that affect the positions of elements with 'scroll-snap-edges', or dynamic changes to values of 'scroll-snap-edges', do not trigger snapping in the absence of a scroll gesture, even if 'mandatory' snapping is requested. | ||