Code shared from the Rust Playground

playground.rs

// Filled circle algorithm with edge softening

fn main() {
    let w = 12;
    let r: f32 = w as f32 / 2.0;
    println!("=================================================");
    println!("radius: {}", r);
    println!("=================================================");
    println!("col,row -> dx,dy -> dist from center -> diff -> alpha");
    println!("=================================================");
    for row in 0..w {
        for col in 0..w {
            let dx = (col as f32 + 0.5 - r).abs();
            let dy = (row as f32 + 0.5 - r).abs();
            let dist = ((dx*dx + dy*dy) as f32).sqrt();
            let diff = dist - r;
            let alpha: u8;
            if diff > 1.0 {
                alpha = 0;
            }
            else if diff > 0.0 && diff < 1.0 {
                alpha = ((1.0 - diff) * 255.0) as u8;
            }
            else {
                alpha = 255;
            }
            println!("{},{} -> {},{} -> {} -> {} -> {}", col, row, dx, dy, dist, diff, alpha);
        }
        println!("=================================================");
    }
}