Arrow Head Generalization

crates/bevy_gizmos/src/arrows.rs

@@ -12,8 +12,29 @@ pub struct ArrowBuilder<'a, 's> {
     gizmos: &'a mut Gizmos<'s>,
     start: Vec3,
     end: Vec3,
+    front: ArrowHead,
+    back: ArrowHead,
     color: Color,
     tip_length: f32,
+    double_ended: bool,
+}
+
+/// Represents how the end of an arrow should be drawn.
+/// See also [`Gizmos::arrow`] and [`Gizmos::arrow_2d`].
+#[derive(Default, Debug, Copy, Clone)]
+pub enum ArrowHead {
+    /// No head. Putting this on both ends causes the arrow to just be a line.
+    None,
+    /// General-purpose arrow head with four tips for viewing from any angle. Default
+    #[default]
+    Normal,
+    /// Two-tip arrow head, facing as close to `towards` as possible while still being inline with the arrow body
+    Billboarded(
+        /// Will attempt to be most visible from this direction.
+        /// - in 3d applications, this would typically be the camera position.
+        /// - in 2d applications, this would typically be [`Vec3::Y`] or [`Vec3::Z`]
+        Vec3,
+    ),
 }
 
 impl ArrowBuilder<'_, '_> {
@@ -32,8 +53,47 @@ impl ArrowBuilder<'_, '_> {
     /// # bevy_ecs::system::assert_is_system(system);
     /// ```
     #[doc(alias = "arrow_head_length")]
-    pub fn with_tip_length(&mut self, length: f32) {
+    pub fn with_tip_length(&mut self, length: f32) -> &mut Self {
         self.tip_length = length;
+        self
+    }
+
+    /// Make the arrow double-ended.
+    /// sets both ends of the arrow to [`ArrowHead::Normal`]
+    /// if you want to use a different head, use [`ArrowBuilder::???`]
+    ///
+    /// # Example
+    /// ```
+    /// # use bevy_gizmos::prelude::*;
+    /// # use bevy_render::prelude::*;
+    /// # use bevy_math::prelude::*;
+    /// fn system(mut gizmos: Gizmos) {
+    ///     gizmos.arrow(Vec3::ZERO, Vec3::ONE, Color::GREEN)
+    ///         .double_ended();
+    /// }
+    /// # bevy_ecs::system::assert_is_system(system);
+    /// ```
+    pub fn double_ended(&mut self) -> &mut Self {
+        self.double_ended = true;
+        return self;
+    }
+
+    /// Make the arrow single-ended (the default).
+    ///
+    /// # Example
+    /// ```
+    /// # use bevy_gizmos::prelude::*;
+    /// # use bevy_render::prelude::*;
+    /// # use bevy_math::prelude::*;
+    /// fn system(mut gizmos: Gizmos) {
+    ///     gizmos.arrow(Vec3::ZERO, Vec3::ONE, Color::GREEN)
+    ///         .with_double_ended();
+    /// }
+    /// # bevy_ecs::system::assert_is_system(system);
+    /// ```
+    pub fn with_single_ended(&mut self) -> &mut Self {
+        self.double_ended = false;
+        return self;
     }
 }
 
@@ -53,12 +113,21 @@ impl Drop for ArrowBuilder<'_, '_> {
             Vec3::new(-1., 0., -1.),
         ];
         // - 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);
+        let tips = tips.map(|v| (v.normalize() * self.tip_length));
         for v in tips {
+            // - rotate the world so +x is facing in the same direction as the arrow
+            // - translate over to the tip of the arrow
             // then actually draw the tips
-            self.gizmos.line(self.end, v, self.color);
+            self.gizmos
+                .line(self.end, self.end + (rotation * v), self.color);
+        }
+        if self.double_ended {
+            // same thing but draw starting from the start and use the inverse rotation
+            let rotation = Quat::from_rotation_arc(Vec3::NEG_X, pointing);
+            for v in tips {
+                self.gizmos
+                    .line(self.start, self.start + (rotation * v), self.color);
+            }
         }
     }
 }
@@ -86,6 +155,7 @@ impl<'s> Gizmos<'s> {
             end,
             color,
             tip_length: length / 10.,
+            double_ended: false,
         }
     }