Function grab 

pub fn grab(
    tx: &mut Transaction<'_>,
    options: &GrabOptions,
) -> Result<GrabReport>

Drags the vertices under the brush along one vector.

• Region: every live vertex closer than radius to center (brute-force distance check), each displaced by strength * falloff * direction, where falloff is the Falloff weight of its normalized distance. Unlike inflate, the direction is the caller’s, not the normals’.
• The move is written once, in a single set_positions call over the vertices whose displacement is above 0; an empty region, or a zero direction, writes nothing. History is untouched.

Errors

• OpsError::InvalidInput when the radius is not positive, or any brush number (center, radius, strength) or the direction is not finite.
• OpsError::Store when memory runs out.

Nothing is written in any of these cases.