The widget single cell scrolling methods no longer work as expected from the keyboard

[davep]

Consider the following (slightly over-complicated, but designed to show all the related information) code:

from rich.segment        import Segment
from textual.app         import App, ComposeResult
from textual.widgets     import Header, Footer
from textual.scroll_view import ScrollView
from textual.geometry    import Size
from textual.strip       import Strip

class ScrollViewTest( ScrollView, can_focus=True ):

    def __init__( self, height: int ) -> None:
        super().__init__()
        self.virtual_size = Size( 0, height )

    def render_line( self, y: int ) -> Strip:
        return Strip( [
            Segment( f"{self.scroll_offset.y + y:10}" ),
            Segment( f"{y:10}" ),
            *(
                [ Segment( f"{' ' * 10}scroll_offset.y == {self.scroll_offset.y}") ]
                if y == 0 else []
            )
        ] )

class ScrollTestApp( App[ None ] ):

    def compose( self ) -> ComposeResult:
        yield Header()
        yield ScrollViewTest( 1000 )
        yield Footer()

    def on_mount( self ) -> None:
        self.query_one( ScrollViewTest ).focus()

if __name__ == "__main__":
    ScrollTestApp().run()

If you run it and, using just the keyboard, try and scroll down just one line, or up one line, you'll find it's not possible. It will always scroll two lines.

It seems that this was introduced as part of #1689 ("Scroll sensitivity"). Two App-level properties were introduced, called scroll_sensitivity_x and scroll_sensitivity_y. Both properties say they dictate the number of cells to scroll in the given direction "with wheel or trackpad". However, they're used in the related Widget.scroll_* methods regardless of the input method.

At the very least scroll_up, scroll_down, scroll_left and scroll_right should be modified to only apply the sensitivity setting if the input device is a pointing device rather than a key binding.

[davep]

Bumping this to TODO and claiming it as it intersects with what'll need doing with #1774. This should be merged first I feel, then #1774 can follow (or it may be done as part of the same change; I've yet to decide -- either way I'm promoting it and claiming it).

[willmcgugan]

I think we need to differentiate between mouse scroll (which should respect sensitivity and keyboard scroll which should not respect sensitivity). Suspect we will need to add a "mouse_initiated" bool to the scroll up / down / left / right methods.

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