WICG
Add property for whether dragging the pointer scrolls
In the Pointer Events hackathon it was discussed that there's no good way to know if a user would expect a pointermove event to trigger scrolling. Eg. for a library trying to implement a custom scroller that behaves like the native OS scrollers (eg. iScroll). A naive thing to do is to trigger scrolling for pointerType="touch" only, but that won't handle the case of touch-like stylus devices (eg. Samsung SPen).
We should just add a new property to InputDeviceCapabilities that indicates whether this is a pointer where movement typically causes scrolling. For chromium this will probably always have the same value as firesTouchEvents.
/cc @scottgonzalez @jacobrossi @mustaqahmed @dtapuska @tdresser
Probably the main question here is what the property name should be. Ideas:
- draggingScrolls
- pointerMovementScrolls
- scrollByDragging
Should the name be specific to scroll? Or should it also refer to whether pointers can cause zoom?
I think it should be scroll-specific. Eg. I think the SPen can scroll but not zoom (and if not, certainly it would be reasonable for some pens to act that way).
Note that it's tempting to describe this as "is direct manipulation" - i.e. is the input metaphor one where the user is directly grabbing things on the screen. I think I'll put some text like that in the prose, but IMHO it's probably best to keep the property name very concrete around a specific capability.
Let's leave this issue open until there's been some more discussion and the tests and polyfill have been updated (not something I expect to do before I get back from vacation late Aug).