Show preview when MouseEditMove in cubic_splines example

examples/math/cubic_splines.rs

@@ -57,6 +57,7 @@ fn setup(mut commands: Commands) {
 
     let default_control_data = ControlPoints {
         points_and_tangents: default_points.into_iter().zip(default_tangents).collect(),
+        preview_point: None,
     };
 
     let curve = form_curve(&default_control_data, spline_mode, cycling_mode);
@@ -146,6 +147,7 @@ struct Curve(Option<CubicCurve<Vec2>>);
 #[derive(Clone, Resource)]
 struct ControlPoints {
     points_and_tangents: Vec<(Vec2, Vec2)>,
+    preview_point: Option<(Vec2, Vec2)>,
 }
 
 /// This system is responsible for updating the [`Curve`] when the [control points] or active modes
@@ -205,9 +207,14 @@ fn form_curve(
     spline_mode: SplineMode,
     cycling_mode: CyclingMode,
 ) -> Curve {
-    let (points, tangents): (Vec<_>, Vec<_>) =
+    let (mut points, mut tangents): (Vec<_>, Vec<_>) =
         control_points.points_and_tangents.iter().copied().unzip();
 
+    if let Some((preview_point, preview_tangent)) = control_points.preview_point {
+        points.push(preview_point);
+        tangents.push(preview_tangent);
+    }
+
     match spline_mode {
         SplineMode::Hermite => {
             let spline = CubicHermite::new(points, tangents);
@@ -350,6 +357,7 @@ fn handle_mouse_press(
 
                 // The start of the click-and-drag motion represents the point to add,
                 // while the difference with the current position represents the tangent.
+                control_points.preview_point = None;
                 control_points.points_and_tangents.push((point, tangent));
 
                 // Reset the edit move since we've consumed it.
@@ -363,6 +371,7 @@ fn handle_mouse_press(
 fn draw_edit_move(
     edit_move: Res<MouseEditMove>,
     mouse_position: Res<MousePosition>,
+    mut control_points: ResMut<ControlPoints>,
     mut gizmos: Gizmos,
     camera: Single<(&Camera, &GlobalTransform)>,
 ) {
@@ -384,6 +393,10 @@ fn draw_edit_move(
         return;
     };
 
+    // Set preview_point for previewing the curve while dragging the tangent
+    let tangent = end - start;
+    control_points.preview_point = Some((start, tangent));
+
     gizmos.circle_2d(start, 10.0, Color::srgb(0.0, 1.0, 0.7));
     gizmos.circle_2d(start, 7.0, Color::srgb(0.0, 1.0, 0.7));
     gizmos.arrow_2d(start, end, Color::srgb(1.0, 0.0, 0.7));