Feature: new Quartiles from precalculated values

src/data/quartiles.rs

@@ -62,6 +62,33 @@ impl Quartiles {
         }
     }
 
+    /// Create a new quartiles struct with pre-calculated values.
+    ///
+    /// - `s`: The array of the original values
+    /// - **returns** The newly created quartiles
+    ///
+    /// ```rust
+    /// use plotters::prelude::*;
+    ///
+    /// let quartiles = Quartiles::new_from_values(&[2, 24, 31, 39, 45]);
+    /// assert_eq!(quartiles.values(), [2.0, 24.0, 31.0, 39.0, 45.0]);
+    /// ```
+    pub fn new_from_values<T: Into<f64> + Copy + PartialOrd>(s: &[T; 5]) -> Self {
+        let s = s.to_owned();
+        assert!(s[0] <= s[1]);
+        assert!(s[1] <= s[2]);
+        assert!(s[2] <= s[3]);
+        assert!(s[3] <= s[4]);
+
+        Self {
+            lower_fence: s[0].into(),
+            lower: s[1].into(),
+            median: s[2].into(),
+            upper: s[3].into(),
+            upper_fence: s[4].into(),
+        }
+    }
+
     /// Get the quartiles values.
     ///
     /// - **returns** The array [lower fence, lower quartile, median, upper quartile, upper fence]

src/drawing/backend_impl/piston.rs

@@ -34,6 +34,14 @@ fn make_point_pair(a: BackendCoord, b: BackendCoord, scale: f64) -> [f64; 4] {
     ]
 }
 
+fn make_circle(center: BackendCoord, radius: u32, scale: f64) -> [f64; 4] {
+    circle(
+        center.0 as f64 * scale,
+        center.1 as f64 * scale,
+        radius as f64 * scale,
+    )
+}
+
 impl<'a, 'b> PistonBackend<'a, 'b> {
     pub fn new(size: (u32, u32), scale: f64, context: Context, graphics: &'b mut G2d<'a>) -> Self {
         Self {
@@ -150,7 +158,7 @@ impl<'a, 'b> DrawingBackend for PistonBackend<'a, 'b> {
         style: &S,
         fill: bool,
     ) -> Result<(), DrawingErrorKind<Self::ErrorType>> {
-        let rect = circle(center.0 as f64, center.1 as f64, radius as f64);
+        let rect = make_circle(center, radius, self.scale);
         if fill {
             ellipse(
                 make_piston_rgba(&style.as_color()),
@@ -204,3 +212,13 @@ pub fn draw_piston_window<F: FnOnce(PistonBackend) -> Result<(), Box<dyn std::er
     }
     None
 }
+
+#[cfg(test)]
+mod test {
+    use super::*;
+    #[test]
+    fn test_make_circle() {
+        assert_eq!(make_circle((1, 1), 0, 1.0), [1.0, 1.0, 0.0, 0.0]);
+        assert_eq!(make_circle((1, 2), 3, 4.0), [-8.0, -4.0, 24.0, 24.0]);
+    }
+}