(s as f64 / 60.0): 秒を分で表す（0.0 - 1.0）
*360.0: 分に対する角度を度数法で計算
-90.0: 0秒のときに秒針が12時方向を指すように90度補正

(m as f64 + s as f64/ 60.0): 分に秒による経過分を加算
/60.0: 分を時間で表す（0.0 - 1.0）
*360.0: 時間に対する角度を度数法で計算
-90.0: 0分のときに分針が12時方向を指すように90度補正

(h as f64 % 12.0 + m as f64 / 60.0 + s as f64 / 3600.0):
h % 12.0: 12時間制にするため、時を12で割った余りを計算
分と秒を時間に変換して加算
/12.0: 時を12時間で割って、12時間に対する割合を計算
*360.0: 12時間に対する角度を度数法で計算
-90.0: 0時のときに時針が12時方向を指すように90度補正

// 省略

#[wasm_bindgen]
pub fn clock_png(h : u32,m : u32,s : u32) -> String{
    let mut img = DynamicImage::new_rgba8(320,320);
    // 円の中心座標
    let center_x = img.width() / 2;
    let center_y = img.height() / 2;
    draw_filled_circle_mut(&mut img, (center_x as i32, center_y as i32), 155, Rgba([0, 0, 0, 255]));
    draw_filled_circle_mut(&mut img, (center_x as i32, center_y as i32), 153, Rgba([0, 0, 0, 0]));
    draw_filled_circle_mut(&mut img, (center_x as i32, center_y as i32), 5, Rgba([0, 0, 0, 255]));

    let s_angle = ((s as f64 / 60.0) * 360.0- 90.0).to_radians();
    draw_line_segment_mut(&mut img,(center_x as f32, center_y as f32),(center_x as f32 + 140.0 * s_angle.cos() as f32,center_y as f32 + 140.0 * s_angle.sin() as f32),Rgba([0, 0, 0, 255])); // 秒針

    let m_angle = (((m as f64 + s  as f64/ 60.0) / 60.0) * 360.0 - 90.0).to_radians();
    draw_line_segment_mut(&mut img,(center_x as f32, center_y as f32),(center_x as f32 + 120.0 * m_angle.cos() as f32,center_y as f32 + 120.0 * m_angle.sin() as f32),Rgba([0, 0, 0, 255])); // 長針

    let h_angle = (((h as f64 % 12.0 + m as f64 / 60.0 + s as f64 / 3600.0) / 12.0) * 360.0 - 90.0).to_radians();
    draw_line_segment_mut(&mut img,(center_x as f32, center_y as f32),(center_x as f32 + 80.0 * h_angle.cos() as f32,center_y as f32 + 80.0 * h_angle.sin() as f32),Rgba([0, 0, 0, 255])); // 短針

    let mut buffer = Cursor::new(Vec::new());
    img.write_to(&mut buffer, ImageFormat::Png).unwrap();
    let base64_string = general_purpose::STANDARD.encode(buffer.get_ref());
    // データURL形式で返す
    format!("data:image/png;base64,{}", base64_string)
}


// 省略

// 省略

setInterval(()=>{
  const now = new Date();
  const h = now.getHours();
  const m = now.getMinutes();
  const s = now.getSeconds();
  document.getElementById("mainImg").src = clock_png(h,m,s);
}, 1000);

// 省略