Add double end arrow to gizmos (#11890)

# Objective

- Implement double ended arrows, suggestion of #9400

## Solution

- Creation of new field and method to the `ArrowBuilder`

---

## Changelog

### Added
- New field `ArrowBuilder::double_ended`
- New method `ArrowBuilder::with_double_end` to redefine the
double_ended field

## Additional

I added this in the 3d_gizmos example, that's the result:


![image](https://github.com/bevyengine/bevy/assets/126117294/2f8a93eb-4952-401a-b600-b1454cf898a9)

I added this arrow in the 2d_gizmos example too:


![image](https://github.com/bevyengine/bevy/assets/126117294/c46b4871-8acf-4711-9ca8-c2df36c0464b)

---------

Co-authored-by: Afonso Lage <[email protected]>
Co-authored-by: Pablo Reinhardt <[email protected]>

Author: 3 people

crates/bevy_gizmos/src/arrows.rs

@@ -17,6 +17,7 @@ pub struct ArrowBuilder<'a, 'w, 's, T: GizmoConfigGroup> {
     start: Vec3,
     end: Vec3,
     color: Color,
+    double_ended: bool,
     tip_length: f32,
 }
 
@@ -41,6 +42,13 @@ impl<T: GizmoConfigGroup> ArrowBuilder<'_, '_, '_, T> {
         self.tip_length = length;
         self
     }
+
+    /// Adds another tip to the arrow, appended in the start point.
+    /// the default is only one tip at the end point.
+    pub fn with_double_end(mut self) -> Self {
+        self.double_ended = true;
+        self
+    }
 }
 
 impl<T: GizmoConfigGroup> Drop for ArrowBuilder<'_, '_, '_, T> {
@@ -53,8 +61,8 @@ impl<T: GizmoConfigGroup> Drop for ArrowBuilder<'_, '_, '_, T> {
         self.gizmos.line(self.start, self.end, self.color);
         // now the hard part is to draw the head in a sensible way
         // put us in a coordinate system where the arrow is pointing towards +x and ends at the origin
-        let pointing = (self.end - self.start).normalize();
-        let rotation = Quat::from_rotation_arc(Vec3::X, pointing);
+        let pointing_end = (self.end - self.start).normalize();
+        let rotation_end = Quat::from_rotation_arc(Vec3::X, pointing_end);
         let tips = [
             Vec3::new(-1., 1., 0.),
             Vec3::new(-1., 0., 1.),
@@ -64,11 +72,21 @@ impl<T: GizmoConfigGroup> Drop for ArrowBuilder<'_, '_, '_, T> {
         // - extend the vectors so their length is `tip_length`
         // - rotate the world so +x is facing in the same direction as the arrow
         // - translate over to the tip of the arrow
-        let tips = tips.map(|v| rotation * (v.normalize() * self.tip_length) + self.end);
-        for v in tips {
+        let tips_end = tips.map(|v| rotation_end * (v.normalize() * self.tip_length) + self.end);
+        for v in tips_end {
             // then actually draw the tips
             self.gizmos.line(self.end, v, self.color);
         }
+        if self.double_ended {
+            let pointing_start = (self.start - self.end).normalize();
+            let rotation_start = Quat::from_rotation_arc(Vec3::X, pointing_start);
+            let tips_start =
+                tips.map(|v| rotation_start * (v.normalize() * self.tip_length) + self.start);
+            for v in tips_start {
+                // draw the start points tips
+                self.gizmos.line(self.start, v, self.color);
+            }
+        }
     }
 }
 
@@ -100,6 +118,7 @@ impl<'w, 's, T: GizmoConfigGroup> Gizmos<'w, 's, T> {
             start,
             end,
             color: color.into(),
+            double_ended: false,
             tip_length: length / 10.,
         }
     }

examples/gizmos/2d_gizmos.rs

@@ -89,6 +89,12 @@ fn draw_example_collection(
         Vec2::from_angle(sin / -10. + PI / 2.) * 50.,
         YELLOW,
     );
+
+    // You can create more complex arrows using the arrow builder.
+    gizmos
+        .arrow_2d(Vec2::ZERO, Vec2::from_angle(sin / -10.) * 50., GREEN)
+        .with_double_end()
+        .with_tip_length(10.);
 }
 
 fn update_config(

examples/gizmos/3d_gizmos.rs

@@ -137,6 +137,12 @@ fn draw_example_collection(
         .circle_segments(64);
 
     gizmos.arrow(Vec3::ZERO, Vec3::ONE * 1.5, YELLOW);
+
+    // You can create more complex arrows using the arrow builder.
+    gizmos
+        .arrow(Vec3::new(2., 0., 2.), Vec3::new(2., 2., 2.), ORANGE_RED)
+        .with_double_end()
+        .with_tip_length(0.5);
 }
 
 fn update_config(