Add dashed lines (#16884)

# Objective

- Fixes #16873

## Solution

- Added  `GizmoLineStyle::Dashed {gap_scale, line_scale}`
- The `gap_scale` and `line_scale` describe the lengths of the gaps and
visible line-segments in terms of line-widths. For example, if
`gap_scale == 1.0` and `line_scale == 3.0` the gaps are square and the
the visible segments are three line-widths long.
- The new `GizmoLineStyle` can be used both in 3D and 2D and with both
perspective and orthographic cameras.
- Updated the `2d_gizmos` and `3d_gizmos` examples to include the new
line-style.
- Display a warning, when using negative `gap_scale` or `line_scale`.
- Notably, `Hash` and `Eq` are manually implemented for `GizmoLineStyle`
since both are not implemented for `f32` which prevents deriving these
traits for `GizmoLineStyle`.

## Testing

- The results can be verified visually

---

## Showcase
The following images depict dashed lines with `gap_scale == 3.0` and
`line_scale == 5.0` in perspective 3D and orthographic 2D.


![linestyle-dashed-2d](https://github.com/user-attachments/assets/3541cc55-63c2-4600-882b-3da61f9472bd)

![linestyle-dashed-3d](https://github.com/user-attachments/assets/6b106352-8e74-44a0-b481-46510d4f9148)

---------

Co-authored-by: Hennadii Chernyshchyk <genaloner@gmail.com>

crates/bevy_gizmos/src/config.rs

@@ -14,6 +14,7 @@ use bevy_reflect::{std_traits::ReflectDefault, Reflect, TypePath};
 use bevy_utils::TypeIdMap;
 use core::{
     any::TypeId,
+    hash::Hash,
     ops::{Deref, DerefMut},
     panic,
 };
@@ -36,7 +37,7 @@ pub enum GizmoLineJoint {
 }
 
 /// An enum used to configure the style of gizmo lines, similar to CSS line-style
-#[derive(Copy, Clone, Debug, Default, Hash, PartialEq, Eq, Reflect)]
+#[derive(Copy, Clone, Debug, Default, PartialEq, Reflect)]
 #[non_exhaustive]
 pub enum GizmoLineStyle {
     /// A solid line without any decorators
@@ -44,6 +45,34 @@ pub enum GizmoLineStyle {
     Solid,
     /// A dotted line
     Dotted,
+    /// A dashed line with configurable gap and line sizes
+    Dashed {
+        /// The length of the gap in `line_width`s
+        gap_scale: f32,
+        /// The length of the visible line in `line_width`s
+        line_scale: f32,
+    },
+}
+
+impl Eq for GizmoLineStyle {}
+
+impl Hash for GizmoLineStyle {
+    fn hash<H: core::hash::Hasher>(&self, state: &mut H) {
+        match self {
+            Self::Solid => {
+                0u64.hash(state);
+            }
+            Self::Dotted => 1u64.hash(state),
+            Self::Dashed {
+                gap_scale,
+                line_scale,
+            } => {
+                2u64.hash(state);
+                gap_scale.to_bits().hash(state);
+                line_scale.to_bits().hash(state);
+            }
+        }
+    }
 }
 
 /// A trait used to create gizmo configs groups.

crates/bevy_gizmos/src/lib.rs

@@ -81,7 +81,7 @@ use bevy_ecs::{
     schedule::{IntoSystemConfigs, SystemSet},
     system::{Res, ResMut, Resource},
 };
-use bevy_math::Vec4;
+use bevy_math::{Vec3, Vec4};
 use bevy_reflect::TypePath;
 
 #[cfg(all(
@@ -419,6 +419,9 @@ fn extract_gizmo_data(
     handles: Extract<Res<GizmoHandles>>,
     config: Extract<Res<GizmoConfigStore>>,
 ) {
+    use bevy_utils::warn_once;
+    use config::GizmoLineStyle;
+
     for (group_type_id, handle) in &handles.handles {
         let Some((config, _)) = config.get_config_dyn(group_type_id) else {
             continue;
@@ -438,12 +441,30 @@ fn extract_gizmo_data(
             0
         };
 
+        let (gap_scale, line_scale) = if let GizmoLineStyle::Dashed {
+            gap_scale,
+            line_scale,
+        } = config.line.style
+        {
+            if gap_scale <= 0.0 {
+                warn_once!("When using gizmos with the line style `GizmoLineStyle::Dashed{{..}}` the gap scale should be greater than zero.");
+            }
+            if line_scale <= 0.0 {
+                warn_once!("When using gizmos with the line style `GizmoLineStyle::Dashed{{..}}` the line scale should be greater than zero.");
+            }
+            (gap_scale, line_scale)
+        } else {
+            (1.0, 1.0)
+        };
+
         commands.spawn((
             LineGizmoUniform {
                 world_from_local: Affine3::from(&Affine3A::IDENTITY).to_transpose(),
                 line_width: config.line.width,
                 depth_bias: config.depth_bias,
                 joints_resolution,
+                gap_scale,
+                line_scale,
                 #[cfg(feature = "webgl")]
                 _padding: Default::default(),
             },
@@ -471,9 +492,12 @@ struct LineGizmoUniform {
     depth_bias: f32,
     // Only used by gizmo line t if the current configs `line_joints` is set to `GizmoLineJoint::Round(_)`
     joints_resolution: u32,
+    // Only used if the current configs `line_style` is set to `GizmoLineStyle::Dashed{_}`
+    gap_scale: f32,
+    line_scale: f32,
     /// WebGL2 structs must be 16 byte aligned.
     #[cfg(feature = "webgl")]
-    _padding: f32,
+    _padding: Vec3,
 }
 
 /// A collection of gizmos.

crates/bevy_gizmos/src/lines.wgsl

@@ -8,9 +8,12 @@ struct LineGizmoUniform {
     world_from_local: mat3x4<f32>,
     line_width: f32,
     depth_bias: f32,
+    _joints_resolution: u32,
+    gap_scale: f32,
+    line_scale: f32,
 #ifdef SIXTEEN_BYTE_ALIGNMENT
     // WebGL2 structs must be 16 byte aligned.
-    _padding: vec2<f32>,
+    _padding: vec3<f32>,
 #endif
 }
 
@@ -28,6 +31,7 @@ struct VertexOutput {
     @builtin(position) clip_position: vec4<f32>,
     @location(0) color: vec4<f32>,
     @location(1) uv: f32,
+    @location(2) line_fraction: f32,
 };
 
 const EPSILON: f32 = 4.88e-04;
@@ -126,7 +130,9 @@ fn vertex(vertex: VertexInput) -> VertexOutput {
 
     var clip_position = vec4(clip.w * ((2. * screen) / resolution - 1.), depth, clip.w);
 
-    return VertexOutput(clip_position, color, uv);
+    let line_fraction = 2.0 * line_gizmo.line_scale / (line_gizmo.gap_scale + line_gizmo.line_scale);
+    uv /= (line_gizmo.gap_scale + line_gizmo.line_scale) / 2.0;
+    return VertexOutput(clip_position, color, uv, line_fraction);
 }
 
 fn clip_near_plane(a: vec4<f32>, b: vec4<f32>) -> vec4<f32> {
@@ -147,6 +153,7 @@ struct FragmentInput {
     @builtin(position) position: vec4<f32>,
     @location(0) color: vec4<f32>,
     @location(1) uv: f32,
+    @location(2) line_fraction: f32,
 };
 
 struct FragmentOutput {
@@ -168,3 +175,15 @@ fn fragment_dotted(in: FragmentInput) -> FragmentOutput {
     
     return FragmentOutput(vec4(in.color.xyz, in.color.w * alpha));
 }
+
+@fragment
+fn fragment_dashed(in: FragmentInput) -> FragmentOutput {
+#ifdef PERSPECTIVE
+    let uv = in.uv;
+#else
+    let uv = in.uv * in.position.w;
+#endif
+    let alpha = 1.0 - floor(min((uv % 2.0) / in.line_fraction, 1.0));
+    
+    return FragmentOutput(vec4(in.color.xyz, in.color.w * alpha));
+}

crates/bevy_gizmos/src/pipeline_2d.rs

@@ -118,6 +118,7 @@ impl SpecializedRenderPipeline for LineGizmoPipeline {
         let fragment_entry_point = match key.line_style {
             GizmoLineStyle::Solid => "fragment_solid",
             GizmoLineStyle::Dotted => "fragment_dotted",
+            GizmoLineStyle::Dashed { .. } => "fragment_dashed",
         };
 
         RenderPipelineDescriptor {

crates/bevy_gizmos/src/pipeline_3d.rs

@@ -124,6 +124,7 @@ impl SpecializedRenderPipeline for LineGizmoPipeline {
         let fragment_entry_point = match key.line_style {
             GizmoLineStyle::Solid => "fragment_solid",
             GizmoLineStyle::Dotted => "fragment_dotted",
+            GizmoLineStyle::Dashed { .. } => "fragment_dashed",
         };
 
         RenderPipelineDescriptor {

crates/bevy_gizmos/src/retained.rs

@@ -106,6 +106,9 @@ pub(crate) fn extract_linegizmos(
 ) {
     use bevy_math::Affine3;
     use bevy_render::sync_world::{MainEntity, TemporaryRenderEntity};
+    use bevy_utils::warn_once;
+
+    use crate::config::GizmoLineStyle;
 
     let mut values = Vec::with_capacity(*previous_len);
     for (entity, gizmo, transform, render_layers) in &query {
@@ -115,6 +118,21 @@ pub(crate) fn extract_linegizmos(
         } else {
             0
         };
+        let (gap_scale, line_scale) = if let GizmoLineStyle::Dashed {
+            gap_scale,
+            line_scale,
+        } = gizmo.line_config.style
+        {
+            if gap_scale <= 0.0 {
+                warn_once!("when using gizmos with the line style `GizmoLineStyle::Dashed{{..}}` the gap scale should be greater than zero");
+            }
+            if line_scale <= 0.0 {
+                warn_once!("when using gizmos with the line style `GizmoLineStyle::Dashed{{..}}` the line scale should be greater than zero");
+            }
+            (gap_scale, line_scale)
+        } else {
+            (1.0, 1.0)
+        };
 
         values.push((
             LineGizmoUniform {
@@ -122,6 +140,8 @@ pub(crate) fn extract_linegizmos(
                 line_width: gizmo.line_config.width,
                 depth_bias: gizmo.depth_bias,
                 joints_resolution,
+                gap_scale,
+                line_scale,
                 #[cfg(feature = "webgl")]
                 _padding: Default::default(),
             },

examples/gizmos/2d_gizmos.rs

@@ -142,6 +142,10 @@ fn update_config(
     if keyboard.just_pressed(KeyCode::KeyU) {
         config.line.style = match config.line.style {
             GizmoLineStyle::Solid => GizmoLineStyle::Dotted,
+            GizmoLineStyle::Dotted => GizmoLineStyle::Dashed {
+                gap_scale: 3.0,
+                line_scale: 5.0,
+            },
             _ => GizmoLineStyle::Solid,
         };
     }
@@ -169,6 +173,10 @@ fn update_config(
     if keyboard.just_pressed(KeyCode::KeyI) {
         my_config.line.style = match my_config.line.style {
             GizmoLineStyle::Solid => GizmoLineStyle::Dotted,
+            GizmoLineStyle::Dotted => GizmoLineStyle::Dashed {
+                gap_scale: 3.0,
+                line_scale: 5.0,
+            },
             _ => GizmoLineStyle::Solid,
         };
     }

examples/gizmos/3d_gizmos.rs

@@ -237,6 +237,10 @@ fn update_config(
     if keyboard.just_pressed(KeyCode::KeyU) {
         config.line.style = match config.line.style {
             GizmoLineStyle::Solid => GizmoLineStyle::Dotted,
+            GizmoLineStyle::Dotted => GizmoLineStyle::Dashed {
+                gap_scale: 3.0,
+                line_scale: 5.0,
+            },
             _ => GizmoLineStyle::Solid,
         };
     }
@@ -264,6 +268,10 @@ fn update_config(
     if keyboard.just_pressed(KeyCode::KeyI) {
         my_config.line.style = match my_config.line.style {
             GizmoLineStyle::Solid => GizmoLineStyle::Dotted,
+            GizmoLineStyle::Dotted => GizmoLineStyle::Dashed {
+                gap_scale: 3.0,
+                line_scale: 5.0,
+            },
             _ => GizmoLineStyle::Solid,
         };
     }