Plot: estimate bounds for generator functions

egui/src/widgets/plot/items/values.rs

@@ -264,13 +264,21 @@ impl Values {
     }
 
     pub(super) fn get_bounds(&self) -> PlotBounds {
+        if self.values.is_empty() {
+            if let Some(generator) = &self.generator {
+                generator.estimate_bounds()
+            } else {
+                PlotBounds::NOTHING
+            }
+        } else {
             let mut bounds = PlotBounds::NOTHING;
-        self.values
-            .iter()
-            .for_each(|value| bounds.extend_with(value));
+            for value in &self.values {
+                bounds.extend_with(value);
+            }
             bounds
         }
     }
+}
 
 // ----------------------------------------------------------------------------
 
@@ -333,6 +341,20 @@ struct ExplicitGenerator {
     points: usize,
 }
 
+impl ExplicitGenerator {
+    fn estimate_bounds(&self) -> PlotBounds {
+        let min_x = *self.x_range.start();
+        let max_x = *self.x_range.end();
+        let min_y = (self.function)(min_x);
+        let max_y = (self.function)(max_x);
+        // TODO: sample some more points
+        PlotBounds {
+            min: [min_x, min_y],
+            max: [max_x, max_y],
+        }
+    }
+}
+
 // ----------------------------------------------------------------------------
 
 /// Result of [`super::PlotItem::find_closest()`] search, identifies an element inside the item for immediate use