RFR: 8334874: Horizontal scroll events from touch pads should scroll the TabPane tabs [v3]

[Jose Pereda]

On Mon, 24 Jun 2024 23:29:07 GMT, Andy Goryachev <angorya at openjdk.org> wrote:

>> Jose Pereda has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Add tests for all four sides
>
> modules/javafx.controls/src/main/java/javafx/scene/control/skin/TabPaneSkin.java line 947:
> 
>> 945:                     case BOTTOM:
>> 946:                         // Consider vertical scroll events (dy > dx) from mouse wheel and trackpad,
>> 947:                         // and horizontal scroll events from a trackpad (dx > dy)
> 
> Maybe we should explain why - to preserve the existing behavior with the mouse (scrolling up/down)?
> 
> The trackpad events can have both `dx` and `dy` of various magnitude, both non-zero, so the logic seems to me a bit contrived - like filtering some events, although at the end it still feels ok.
> 
> What do you think?

(sorry I missed to reply)

I believe the comment already states what are we taking into account, but this is a more detailed explanation:

- a mouse wheel only has vertical scroll events (`dx == 0`, so `abs(dy) > abs(dx)`), then we just take `dy` to produce the horizontal scroll offset.
- a trackpad has both scroll events, and we take whichever is bigger. Typically the user will do a horizontal scrolling if tabs are horizontally laid out, and therefore abs(dy) <<< abs(dx), so we take `dx` to produce the horizontal scroll offset, ignoring the smaller `dy` (that wouldn't have any effect in any case).

I'm happy to reword the comment if needed.

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PR Review Comment: https://git.openjdk.org/jfx/pull/1486#discussion_r1689397250