Function getKeyGestureFragment

Returns a GestureFragment for the given events. Only "keydown" events will be considered.

If there are no "keydown" events in the given list of events, returns false.

The deltas of all events are summed together before determining final delta and direction.

If the events are of conflicting types, i.e. some scroll, some zoom, then the intent will be "unknown" and the direction will be "ambiguous".

Otherwise, if the deltas sum up to 0, the direction will be "none".

IMPORTANT NOTES ON THE DELTA VALUES

For key gestures the deltas are unreliable. You should not assume they correspond to the would-be scroll or zoom amount that the browser would do. But they can be used to determine relative amounts for animating, etc.

Key press events can be divided into 3 categories: that scroll by a "line" (e.g. arrow keys), by a "page" (e.g. PageUp/PageDown) or by the full content height/width (e.g. Home/End). The actual scroll amount that would result from the event is dependent on the browser, the window size or the element's scroll width/height, so ours can only be a best guess.

Since the actual pixel equivalent is browser specific, we use reasonable default values of delta for each of these "line", "page" or "content" modes, similar to what getWheelGestureFragment does:

• For "line", then a configurable fixed value is used (settings.deltaLineHeight).
• For "page", then a configurable fixed value is used (settings.deltaPageHeight).
• For "content", the element's scroll height is used if given, otherwise the viewport height (same as "page"). We do not try to get the current scroll height of the target element, (which would be the best guess value of deltaY in case of Home/End key presses), as that would either involve an asynchronous action or would result in forced layout. If the caller is already tracking the scroll height of the target, you can pass this as an argument. Otherwise, we'll default to using the viewport height, same as for PageUp/Down.

If the key gesture fragment is a result of multiple events that were accumulated, the deltas are summed as usual, e.g. if a "page" is equal to 20 "lines", then pressing PageDown and then 10 times Up, would result in a delta equal to 10 "lines" down.

For zoom intents, deltaZ gives a relative change of scale, whereby each press of + or - steps up by 15% or down by ~13% (1 / 1.15 to be exact) since the previous one.