Fix plot auto bounds

CHANGELOG.md

@@ -32,6 +32,7 @@ NOTE: [`epaint`](epaint/CHANGELOG.md), [`eframe`](eframe/CHANGELOG.md), [`egui-w
 * Fixed dead-lock when alt-tabbing while also showing a tooltip ([#1618](https://github.com/emilk/egui/pull/1618)).
 * Fixed `ScrollArea` scrolling when editing an unrelated `TextEdit` ([#1779](https://github.com/emilk/egui/pull/1779)).
 * Fixed focus behavior when pressing Tab in a UI with no focused widget ([#1861](https://github.com/emilk/egui/pull/1861)).
+* Fixed automatic plot bounds ([#1865](https://github.com/emilk/egui/pull/1865)).
 
 
 ## 0.18.1 - 2022-05-01

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

@@ -378,15 +378,44 @@ pub struct ExplicitGenerator {
 
 impl ExplicitGenerator {
     fn estimate_bounds(&self) -> PlotBounds {
+        let mut bounds = PlotBounds::NOTHING;
+
+        let mut add_x = |x: f64| {
+            // avoid infinities, as we cannot auto-bound on them!
+            if x.is_finite() {
+                bounds.extend_with_x(x);
+            }
+            let y = (self.function)(x);
+            if y.is_finite() {
+                bounds.extend_with_y(y);
+            }
+        };
+
         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(emilk): sample some more points
-        PlotBounds {
-            min: [min_x, min_y],
-            max: [max_x, max_y],
+
+        add_x(min_x);
+        add_x(max_x);
+
+        if min_x.is_finite() && max_x.is_finite() {
+            // Sample some points in the interval:
+            const N: u32 = 8;
+            for i in 1..N {
+                let t = i as f64 / (N - 1) as f64;
+                let x = crate::lerp(min_x..=max_x, t);
+                add_x(x);
+            }
+        } else {
+            // Try adding some points anyway:
+            for x in [-1, 0, 1] {
+                let x = x as f64;
+                if min_x <= x && x <= max_x {
+                    add_x(x);
+                }
+            }
         }
+
+        bounds
     }
 }
 

egui/src/widgets/plot/mod.rs

@@ -682,8 +682,12 @@ impl Plot {
             auto_bounds = true.into();
         }
 
+        if !bounds.is_valid() {
+            auto_bounds = true.into();
+        }
+
         // Set bounds automatically based on content.
-        if auto_bounds.any() || !bounds.is_valid() {
+        if auto_bounds.any() {
             if auto_bounds.x {
                 bounds.set_x(&min_auto_bounds);
             }
@@ -693,13 +697,13 @@ impl Plot {
             }
 
             for item in &items {
-                // bounds.merge(&item.get_bounds());
+                let item_bounds = item.get_bounds();
 
                 if auto_bounds.x {
-                    bounds.merge_x(&item.get_bounds());
+                    bounds.merge_x(&item_bounds);
                 }
                 if auto_bounds.y {
-                    bounds.merge_y(&item.get_bounds());
+                    bounds.merge_y(&item_bounds);
                 }
             }
 
@@ -714,12 +718,14 @@ impl Plot {
 
         let mut transform = ScreenTransform::new(rect, bounds, center_x_axis, center_y_axis);
 
-        // Enforce equal aspect ratio.
+        // Enforce aspect ratio
         if let Some(data_aspect) = data_aspect {
-            let preserve_y = linked_axes
-                .as_ref()
-                .map_or(false, |group| group.link_y && !group.link_x);
-            transform.set_aspect(data_aspect as f64, preserve_y);
+            if let Some(linked_axes) = &linked_axes {
+                let change_x = linked_axes.link_y && !linked_axes.link_x;
+                transform.set_aspect_by_changing_axis(data_aspect as f64, change_x);
+            } else {
+                transform.set_aspect_by_expanding(data_aspect as f64);
+            }
         }
 
         // Dragging
@@ -766,7 +772,7 @@ impl Plot {
                         max: [box_end_pos.x, box_start_pos.y],
                     };
                     if new_bounds.is_valid() {
-                        *transform.bounds_mut() = new_bounds;
+                        transform.set_bounds(new_bounds);
                         auto_bounds = false.into();
                     } else {
                         auto_bounds = true.into();

egui/src/widgets/plot/transform.rs

@@ -206,8 +206,8 @@ impl ScreenTransform {
         &self.bounds
     }
 
-    pub fn bounds_mut(&mut self) -> &mut PlotBounds {
-        &mut self.bounds
+    pub fn set_bounds(&mut self, bounds: PlotBounds) {
+        self.bounds = bounds;
     }
 
     pub fn translate_bounds(&mut self, mut delta_pos: Vec2) {
@@ -299,23 +299,44 @@ impl ScreenTransform {
         [1.0 / self.dpos_dvalue_x(), 1.0 / self.dpos_dvalue_y()]
     }
 
-    pub fn get_aspect(&self) -> f64 {
+    fn aspect(&self) -> f64 {
         let rw = self.frame.width() as f64;
         let rh = self.frame.height() as f64;
         (self.bounds.width() / rw) / (self.bounds.height() / rh)
     }
 
-    /// Sets the aspect ratio by either expanding the x-axis or contracting the y-axis.
-    pub fn set_aspect(&mut self, aspect: f64, preserve_y: bool) {
-        let current_aspect = self.get_aspect();
+    /// Sets the aspect ratio by expanding the x- or y-axis.
+    ///
+    /// This never contracts, so we don't miss out on any data.
+    pub fn set_aspect_by_expanding(&mut self, aspect: f64) {
+        let current_aspect = self.aspect();
+
+        let epsilon = 1e-5;
+        if (current_aspect - aspect).abs() < epsilon {
+            // Don't make any changes when the aspect is already almost correct.
+            return;
+        }
+
+        if current_aspect < aspect {
+            self.bounds
+                .expand_x((aspect / current_aspect - 1.0) * self.bounds.width() * 0.5);
+        } else {
+            self.bounds
+                .expand_y((current_aspect / aspect - 1.0) * self.bounds.height() * 0.5);
+        }
+    }
+
+    /// Sets the aspect ratio by changing either the X or Y axis (callers choice).
+    pub fn set_aspect_by_changing_axis(&mut self, aspect: f64, change_x: bool) {
+        let current_aspect = self.aspect();
 
         let epsilon = 1e-5;
         if (current_aspect - aspect).abs() < epsilon {
             // Don't make any changes when the aspect is already almost correct.
             return;
         }
 
-        if preserve_y {
+        if change_x {
             self.bounds
                 .expand_x((aspect / current_aspect - 1.0) * self.bounds.width() * 0.5);
         } else {