custom ticks locator

examples/gauss.rs

@@ -29,9 +29,11 @@ fn main() {
     let title: des::figure::Title =
         format!("Normal distribution (\u{03bc}={}, \u{03c3}={})", MU, SIGMA).into();
 
+    let ticks = vec![5.0, 9.0, 11.0, 13.0, 15.0, 17.0, 21.0];
+
     let x_axis = des::Axis::new()
         .with_title("x".into())
-        .with_ticks(Default::default());
+        .with_ticks(des::axis::Ticks::new().with_locator(ticks.into()));
     let y_axis = des::Axis::new().with_title("y".into()).with_ticks(
         des::axis::Ticks::new()
             .with_formatter(Some(des::axis::ticks::PercentFormatter::default().into())),

src/des/axis.rs

@@ -385,6 +385,8 @@ pub mod ticks {
         /// on the axis data range (bounds) and whether the ticks are major or minor
         #[default]
         Auto,
+        /// Specifies the exact locations of the ticks in data space.
+        List(ListLocator),
         /// Places ticks automatically, using the specified number of bins and steps
         MaxN(MaxNLocator),
         /// Places the ticks automatically, using the specified number of bins and multiples of PI.
@@ -403,6 +405,28 @@ pub mod ticks {
         TimeDelta(TimeDeltaLocator),
     }
 
+    /// A locator that places ticks at the specified locations in data space
+    #[derive(Debug, Clone)]
+    pub struct ListLocator(pub Vec<f64>);
+
+    impl From<Vec<f64>> for Locator {
+        fn from(loc: Vec<f64>) -> Self {
+            Locator::List(ListLocator(loc))
+        }
+    }
+
+    impl From<Vec<f64>> for ListLocator {
+        fn from(loc: Vec<f64>) -> Self {
+            ListLocator(loc)
+        }
+    }
+
+    impl From<ListLocator> for Locator {
+        fn from(loc: ListLocator) -> Self {
+            Locator::List(loc)
+        }
+    }
+
     /// A locator that places ticks automatically, using the specified number of bins and steps
     #[derive(Debug, Clone)]
     pub struct MaxNLocator {

src/drawing/ticks.rs

@@ -22,6 +22,7 @@ pub fn locate_num(
         (Locator::Auto, Scale::Log(LogScale { base, .. })) => {
             Ok(LogLocator::new_major(*base).ticks(nb))
         }
+        (Locator::List(locator), _) => Ok(locator.0.clone()),
         (Locator::MaxN(locator), Scale::Auto | Scale::Linear { .. }) => {
             let ticker = MaxN::new(locator.bins, locator.steps.as_slice());
             Ok(ticker.ticks(nb))
@@ -530,7 +531,7 @@ fn auto_label_formatter(
         (Locator::Auto, Scale::Log(LogScale { base, .. })) if *base == 10.0 => {
             Arc::new(SciLabelFormat)
         }
-        (Locator::Auto, _) => {
+        (Locator::Auto, _) | (Locator::List(..), _) => {
             let max = ab.start().abs().max(ab.end().abs());
             if max >= 100000.0 || max < 0.001 {
                 Arc::new(SciLabelFormat)