breshenham.rs

fn ptr_at(pos: Vec2<isize>) -> *mut Px { ... }
    
type Px = u16;

pub unsafe fn line(&mut self, a: Vec2<isize>, b: Vec2<isize>, px: Px) {
    let delta = b - a;
    let delta_abs = delta.map(|e| e.abs() as usize);
    let ptr = ptr_at(a.map(|e| e as usize));
    let dx = if delta.x > 0 { 1 } else { -1 };
    let dy = if delta.y > 0 { 1 } else { -1 } * WIDTH;
    if delta_abs.x > delta_abs.y {
        bresenham(ptr, delta_abs, |p| p.offset(dx), |p| p.offset(dy)).for_each(|p| p.write(px));
    } else {
        bresenham(ptr, delta_abs.yx(), |p| p.offset(dy), |p| p.offset(dx)).for_each(|p| p.write(px));
    }
}

/// x is major axis, y is minor axis (flip as needed).
#[inline(always)]
fn bresenham<P, X, Y>(mut pos: P, delta: Vec2<usize>, mut x: X, mut y: Y) -> impl ExactSizeIterator<Item = P>
    where P: Copy, X: FnMut(P) -> P, Y: FnMut(P) -> P,
{
    let dy2 = (delta.y * 2) as isize;
    let dd2 = dy2 - (delta.x * 2) as isize;
    let mut err = dy2 - delta.x as isize;

    (0..delta.x + 1).map(move |_| {
        err += if err >= 0 {
            pos = y(pos);
            dd2
        } else {
            dy2
        };
        pos = x(pos);
        pos
    })
}