Function draw_circle

std/src/console/drawing.rs:167–219

Draws a circle via `rasops` with `center` and `radius`. This implements the [Midpoint circle algorithm](https://en.wikipedia.org/wiki/Midpoint_circle_algorithm).

(rasops: &mut R, center: PixelsXY, radius: u16)

/// This implements the [Midpoint circle
/// algorithm](https://en.wikipedia.org/wiki/Midpoint_circle_algorithm).
pub fn draw_circle<R>(rasops: &mut R, center: PixelsXY, radius: u16) -> io::Result<()>
where
    R: RasterOps,
{
    fn point<R: RasterOps>(rasops: &mut R, x: i16, y: i16) -> io::Result<()> {
        rasops.draw_pixel(PixelsXY { x, y })
    }

    if radius == 0 {
        return Ok(());
    } else if radius == 1 {
        return rasops.draw_pixel(center);
    }

    let (diameter, radius): (i16, i16) = match radius.checked_mul(2) {
        Some(d) => match i16::try_from(d) {
            Ok(d) => (d, radius as i16),
            Err(_) => return Err(io::Error::new(io::ErrorKind::InvalidInput, "Radius is too big")),
        },
        None => return Err(io::Error::new(io::ErrorKind::InvalidInput, "Radius is too big")),
    };

    let mut x: i16 = radius - 1;
    let mut y: i16 = 0;
    let mut tx: i16 = 1;
    let mut ty: i16 = 1;
    let mut e: i16 = tx - diameter;

    while x >= y {
        point(rasops, center.x + x, center.y - y)?;
        point(rasops, center.x + x, center.y + y)?;
        point(rasops, center.x - x, center.y - y)?;
        point(rasops, center.x - x, center.y + y)?;
        point(rasops, center.x + y, center.y - x)?;
        point(rasops, center.x + y, center.y + x)?;
        point(rasops, center.x - y, center.y - x)?;
        point(rasops, center.x - y, center.y + x)?;

        if e <= 0 {
            y += 1;
            e += ty;
            ty += 2;
        }

        if e > 0 {
            x -= 1;
            tx += 2;
            e += tx - diameter;
        }
    }

    Ok(())
}

/// Draws a circle via `rasops` with `center` and `radius`.
///