Source code for simvx.core.input.drag

"""The drag threshold: how far a pointer travels from its press before the motion is a drag.

A setting on the tree, which every node inherits, and on any node, which its
subtree inherits, per pointer type: a finger lands a good deal further from
where it meant to than a mouse does, and a pen sits between them. The router
reads it once per press, from the node that took the press, and every event of
that press carries the answer as ``PointerEvent.dragging``.
"""

from __future__ import annotations

from collections.abc import Mapping

from .enums import PointerType

__all__ = ["DEFAULT_DRAG_THRESHOLD", "drag_threshold_map"]

#: What a tree starts with, in logical pixels, by pointer type.
DEFAULT_DRAG_THRESHOLD: Mapping[PointerType, float] = {
    PointerType.MOUSE: 4.0,
    PointerType.PEN: 6.0,
    PointerType.TOUCH: 12.0,
}




def drag_threshold_map(value: Mapping[PointerType | str, float] | None) -> dict[PointerType, float] | None:
    """Coerce a ``drag_threshold`` assignment: ``None``, or a map from pointer type to distance.

    Keys take the member or its plain string (``{"touch": 16}``), and a type
    the map leaves out is inherited. A negative distance or an unknown type
    raises naming what is allowed.
    """
    if value is None:
        return None
    if not isinstance(value, Mapping):
        raise TypeError(
            f"drag_threshold takes a mapping from pointer type to distance, or None to inherit; got {value!r}"
        )
    out: dict[PointerType, float] = {}
    for key, distance in value.items():
        try:
            kind = PointerType(key)
        except ValueError:
            allowed = ", ".join(repr(t.value) for t in PointerType)
            raise ValueError(f"drag_threshold has no pointer type {key!r}; expected one of {allowed}") from None
        distance = float(distance)
        if distance < 0:
            raise ValueError(f"drag_threshold for {kind.value} must not be negative, got {distance}")
        out[kind] = distance
    return out