Implemented GizmoPrimitive2d for Arc2d, CircularSegment, CircularSector, and make arc_2d use counter-clockwise angle. (#13610)

# Objective

Fixes #13606.
Also Fixes #13614.

## Solution

Added the missing trait impls, and made `gizmos.arc_2d()` work with a
counter-clockwise angle.
## Testing

- Updated the render_primitives example, and it works.

crates/bevy_gizmos/src/arcs.rs

@@ -22,7 +22,7 @@ where
     ///
     /// # Arguments
     /// - `position` sets the center of this circle.
-    /// - `direction_angle` sets the clockwise  angle in radians between `Vec2::Y` and
+    /// - `direction_angle` sets the counter-clockwise  angle in radians between `Vec2::Y` and
     /// the vector from `position` to the midpoint of the arc.
     /// - `arc_angle` sets the length of this arc, in radians.
     /// - `radius` controls the distance from `position` to this arc, and thus its curvature.
@@ -128,8 +128,10 @@ fn arc_2d_inner(
     (0..resolution + 1).map(move |i| {
         let start = direction_angle - arc_angle / 2.;
 
-        let angle = start + (i as f32 * (arc_angle / resolution as f32));
-        Vec2::from(angle.sin_cos()) * radius
+        let angle =
+            start + (i as f32 * (arc_angle / resolution as f32)) + std::f32::consts::FRAC_PI_2;
+
+        Vec2::new(angle.cos(), angle.sin()) * radius
     })
 }
 

crates/bevy_gizmos/src/primitives/dim2.rs

@@ -6,8 +6,9 @@ use super::helpers::*;
 
 use bevy_color::Color;
 use bevy_math::primitives::{
-    Annulus, BoxedPolygon, BoxedPolyline2d, Capsule2d, Circle, Ellipse, Line2d, Plane2d, Polygon,
-    Polyline2d, Primitive2d, Rectangle, RegularPolygon, Rhombus, Segment2d, Triangle2d,
+    Annulus, Arc2d, BoxedPolygon, BoxedPolyline2d, Capsule2d, Circle, CircularSector,
+    CircularSegment, Ellipse, Line2d, Plane2d, Polygon, Polyline2d, Primitive2d, Rectangle,
+    RegularPolygon, Rhombus, Segment2d, Triangle2d,
 };
 use bevy_math::{Dir2, Mat2, Vec2};
 
@@ -64,6 +65,36 @@ where
     }
 }
 
+// arc 2d
+
+impl<'w, 's, Config, Clear> GizmoPrimitive2d<Arc2d> for Gizmos<'w, 's, Config, Clear>
+where
+    Config: GizmoConfigGroup,
+    Clear: 'static + Send + Sync,
+{
+    type Output<'a> = () where Self: 'a;
+
+    fn primitive_2d(
+        &mut self,
+        primitive: &Arc2d,
+        position: Vec2,
+        angle: f32,
+        color: impl Into<Color>,
+    ) -> Self::Output<'_> {
+        if !self.enabled {
+            return;
+        }
+
+        self.arc_2d(
+            position,
+            angle,
+            primitive.half_angle * 2.0,
+            primitive.radius,
+            color,
+        );
+    }
+}
+
 // circle 2d
 
 impl<'w, 's, Config, Clear> GizmoPrimitive2d<Circle> for Gizmos<'w, 's, Config, Clear>
@@ -88,6 +119,85 @@ where
     }
 }
 
+// circular sector 2d
+
+impl<'w, 's, Config, Clear> GizmoPrimitive2d<CircularSector> for Gizmos<'w, 's, Config, Clear>
+where
+    Config: GizmoConfigGroup,
+    Clear: 'static + Send + Sync,
+{
+    type Output<'a> = () where Self: 'a;
+
+    fn primitive_2d(
+        &mut self,
+        primitive: &CircularSector,
+        position: Vec2,
+        angle: f32,
+        color: impl Into<Color>,
+    ) -> Self::Output<'_> {
+        if !self.enabled {
+            return;
+        }
+
+        let color = color.into();
+
+        // we need to draw the arc part of the sector, and the two lines connecting the arc and the center
+        self.arc_2d(
+            position,
+            angle,
+            primitive.arc.half_angle * 2.0,
+            primitive.arc.radius,
+            color,
+        );
+
+        let start = position
+            + primitive.arc.radius * Mat2::from_angle(angle - primitive.arc.half_angle) * Vec2::Y;
+        let end = position
+            + primitive.arc.radius * Mat2::from_angle(angle + primitive.arc.half_angle) * Vec2::Y;
+        self.line_2d(position, start, color);
+        self.line_2d(position, end, color);
+    }
+}
+
+// circular segment 2d
+
+impl<'w, 's, Config, Clear> GizmoPrimitive2d<CircularSegment> for Gizmos<'w, 's, Config, Clear>
+where
+    Config: GizmoConfigGroup,
+    Clear: 'static + Send + Sync,
+{
+    type Output<'a> = () where Self: 'a;
+
+    fn primitive_2d(
+        &mut self,
+        primitive: &CircularSegment,
+        position: Vec2,
+        angle: f32,
+        color: impl Into<Color>,
+    ) -> Self::Output<'_> {
+        if !self.enabled {
+            return;
+        }
+
+        let color = color.into();
+
+        // we need to draw the arc part of the segment, and the line connecting the two ends
+        self.arc_2d(
+            position,
+            angle,
+            primitive.arc.half_angle * 2.0,
+            primitive.arc.radius,
+            color,
+        );
+
+        let start = position
+            + primitive.arc.radius * Mat2::from_angle(angle - primitive.arc.half_angle) * Vec2::Y;
+        let end = position
+            + primitive.arc.radius * Mat2::from_angle(angle + primitive.arc.half_angle) * Vec2::Y;
+        self.line_2d(end, start, color);
+    }
+}
+
 // ellipse 2d
 
 impl<'w, 's, Config, Clear> GizmoPrimitive2d<Ellipse> for Gizmos<'w, 's, Config, Clear>
@@ -192,8 +302,6 @@ where
             return;
         }
 
-        let rotation = Mat2::from_angle(angle);
-
         // transform points from the reference unit square to capsule "rectangle"
         let [top_left, top_right, bottom_left, bottom_right, top_center, bottom_center] = [
             [-1.0, 1.0],
@@ -215,11 +323,8 @@ where
         self.line_2d(bottom_left, top_left, polymorphic_color);
         self.line_2d(bottom_right, top_right, polymorphic_color);
 
-        // if the capsule is rotated we have to start the arc at a different offset angle,
-        // calculate that here
-        let angle_offset = (rotation * Vec2::Y).angle_between(Vec2::Y);
-        let start_angle_top = angle_offset;
-        let start_angle_bottom = PI + angle_offset;
+        let start_angle_top = angle;
+        let start_angle_bottom = PI + angle;
 
         // draw arcs
         self.arc_2d(

examples/math/render_primitives.rs

@@ -85,6 +85,9 @@ enum PrimitiveSelected {
     ConicalFrustum,
     Torus,
     Tetrahedron,
+    Arc,
+    CircularSector,
+    CircularSegment,
 }
 
 impl std::fmt::Display for PrimitiveSelected {
@@ -99,7 +102,7 @@ impl std::fmt::Display for PrimitiveSelected {
 }
 
 impl PrimitiveSelected {
-    const ALL: [Self; 16] = [
+    const ALL: [Self; 19] = [
         Self::RectangleAndCuboid,
         Self::CircleAndSphere,
         Self::Ellipse,
@@ -116,6 +119,9 @@ impl PrimitiveSelected {
         Self::ConicalFrustum,
         Self::Torus,
         Self::Tetrahedron,
+        Self::Arc,
+        Self::CircularSector,
+        Self::CircularSegment,
     ];
 
     fn next(self) -> Self {
@@ -269,6 +275,25 @@ const TETRAHEDRON: Tetrahedron = Tetrahedron {
     ],
 };
 
+const ARC: Arc2d = Arc2d {
+    radius: BIG_2D,
+    half_angle: std::f32::consts::FRAC_PI_4,
+};
+
+const CIRCULAR_SECTOR: CircularSector = CircularSector {
+    arc: Arc2d {
+        radius: BIG_2D,
+        half_angle: std::f32::consts::FRAC_PI_4,
+    },
+};
+
+const CIRCULAR_SEGMENT: CircularSegment = CircularSegment {
+    arc: Arc2d {
+        radius: BIG_2D,
+        half_angle: std::f32::consts::FRAC_PI_4,
+    },
+};
+
 fn setup_cameras(mut commands: Commands) {
     let start_in_2d = true;
     let make_camera = |is_active| Camera {
@@ -446,6 +471,13 @@ fn draw_gizmos_2d(mut gizmos: Gizmos, state: Res<State<PrimitiveSelected>>, time
         PrimitiveSelected::ConicalFrustum => {}
         PrimitiveSelected::Torus => gizmos.primitive_2d(&ANNULUS, POSITION, angle, color),
         PrimitiveSelected::Tetrahedron => {}
+        PrimitiveSelected::Arc => gizmos.primitive_2d(&ARC, POSITION, angle, color),
+        PrimitiveSelected::CircularSector => {
+            gizmos.primitive_2d(&CIRCULAR_SECTOR, POSITION, angle, color);
+        }
+        PrimitiveSelected::CircularSegment => {
+            gizmos.primitive_2d(&CIRCULAR_SEGMENT, POSITION, angle, color);
+        }
     }
 }
 
@@ -675,5 +707,9 @@ fn draw_gizmos_3d(mut gizmos: Gizmos, state: Res<State<PrimitiveSelected>>, time
         PrimitiveSelected::Tetrahedron => {
             gizmos.primitive_3d(&TETRAHEDRON, POSITION, rotation, color);
         }
+
+        PrimitiveSelected::Arc => {}
+        PrimitiveSelected::CircularSector => {}
+        PrimitiveSelected::CircularSegment => {}
     }
 }