Struct Pen 

pub struct Pen { /* private fields */ }

The turtle an endless figure walks with, one symbol at a time.

The flat mode reads + and - alone, as the plane walk does, and leaves the space symbols inert; the space mode reads them all. Either way the state is a Turtle3d, so a flat figure lies in the xy plane.

The branch stack is reserved once, at the bound the grammar’s brackets allow (grammar::bracket_bound), and a push past it is refused rather than grown, so stepping never allocates. Only an unbalanced grammar reaches the bound; there a later ] restores an older state.

Its position is f64 on on_grid’s grid, not the f32 the cached walk uses, and the turtle’s own pos is unused: the frame turns in f32, the pen moves in f64. Every position an endless figure holds is a grid point, so a re-base by a whole number of steps (shift) is exact, and a step’s length keeps its precision however far the pen walks.

Implementations

impl Pen

pub fn new(mode: TurtleMode, angle: f32, stack_bound: usize) -> Self

A pen at the origin for mode, turning by angle radians, with room for stack_bound open branches.

pub fn read(&mut self, ch: char) -> Option<Drawn>

Read one symbol, and say what it drew, if anything.

pub fn clear_branches(&mut self)

Close every open branch where the turtle stands, and lift the pen: a restarted stream opens its brackets from nothing.

pub fn position(&self) -> [f64; 3]

Where the pen stands, in draw steps.

pub fn stack_capacity(&self) -> usize

The branch stack’s reserved room.

pub fn shift(&mut self, origin: [f64; 3])

Move the origin to origin, a whole number of steps: the pen and every saved branch point move by -origin, exactly, for a grid point within the grid’s reach.

Trait Implementations

impl Clone for Pen

fn clone(&self) -> Pen

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Pen

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.