Render Layers (#1209)

Adds RenderLayers, which enable cameras and entities to opt in to layers that apply to them

crates/bevy_render/src/camera/visible_entities.rs

@@ -24,22 +24,208 @@ impl VisibleEntities {
     }
 }
 
+type LayerMask = u32;
+
+/// An identifier for a rendering layer.
+pub type Layer = u8;
+
+/// Describes which rendering layers an entity belongs to.
+///
+/// Cameras with this component will only render entities with intersecting
+/// layers.
+///
+/// There are 32 layers numbered `0` - [`TOTAL_LAYERS`]. Entities may belong to one or more
+/// layers, or no layer at all.
+///
+/// The [`Default`] instance of `RenderLayers` contains layer `0`, the first layer.
+///
+/// An entity with this component without any layers is invisible.
+///
+/// Entities without this component belong to layer `0`.
+#[derive(Copy, Clone, Reflect, PartialEq, Eq, PartialOrd, Ord)]
+#[reflect(Component)]
+pub struct RenderLayers(LayerMask);
+
+impl std::fmt::Debug for RenderLayers {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_tuple("RenderLayers")
+            .field(&self.iter().collect::<Vec<_>>())
+            .finish()
+    }
+}
+
+impl std::iter::FromIterator<Layer> for RenderLayers {
+    fn from_iter<T: IntoIterator<Item = Layer>>(i: T) -> Self {
+        i.into_iter().fold(Self::none(), |mask, g| mask.with(g))
+    }
+}
+
+/// Defaults to containing to layer `0`, the first layer.
+impl Default for RenderLayers {
+    fn default() -> Self {
+        RenderLayers::layer(0)
+    }
+}
+
+impl RenderLayers {
+    /// The total number of layers supported.
+    pub const TOTAL_LAYERS: usize = std::mem::size_of::<LayerMask>() * 8;
+
+    /// Create a new `RenderLayers` belonging to the given layer.
+    pub fn layer(n: Layer) -> Self {
+        RenderLayers(0).with(n)
+    }
+
+    /// Create a new `RenderLayers` that belongs to all layers.
+    pub fn all() -> Self {
+        RenderLayers(u32::MAX)
+    }
+
+    /// Create a new `RenderLayers` that belongs to no layers.
+    pub fn none() -> Self {
+        RenderLayers(0)
+    }
+
+    /// Create a `RenderLayers` from a list of layers.
+    pub fn from_layers(layers: &[Layer]) -> Self {
+        layers.iter().copied().collect()
+    }
+
+    /// Add the given layer.
+    ///
+    /// This may be called multiple times to allow an entity to belong
+    /// to multiple rendering layers. The maximum layer is `TOTAL_LAYERS - 1`.
+    ///
+    /// # Panics
+    /// Panics when called with a layer greater than `TOTAL_LAYERS - 1`.
+    pub fn with(mut self, layer: Layer) -> Self {
+        assert!(usize::from(layer) < Self::TOTAL_LAYERS);
+        self.0 |= 1 << layer;
+        self
+    }
+
+    /// Removes the given rendering layer.
+    ///
+    /// # Panics
+    /// Panics when called with a layer greater than `TOTAL_LAYERS - 1`.
+    pub fn without(mut self, layer: Layer) -> Self {
+        assert!(usize::from(layer) < Self::TOTAL_LAYERS);
+        self.0 |= 0 << layer;
+        self
+    }
+
+    /// Get an iterator of the layers.
+    pub fn iter(&self) -> impl Iterator<Item = Layer> {
+        let total: Layer = std::convert::TryInto::try_into(Self::TOTAL_LAYERS).unwrap();
+        let mask = *self;
+        (0..total).filter(move |g| RenderLayers::layer(*g).intersects(&mask))
+    }
+
+    /// Determine if a `RenderLayers` intersects another.
+    ///
+    /// `RenderLayers`s intersect if they share any common layers.
+    ///
+    /// A `RenderLayers` with no layers will not match any other
+    /// `RenderLayers`, even another with no layers.
+    pub fn intersects(&self, other: &RenderLayers) -> bool {
+        (self.0 & other.0) > 0
+    }
+}
+
+#[cfg(test)]
+mod rendering_mask_tests {
+    use super::{Layer, RenderLayers};
+
+    #[test]
+    fn rendering_mask_sanity() {
+        assert_eq!(
+            RenderLayers::TOTAL_LAYERS,
+            32,
+            "total layers is what we think it is"
+        );
+        assert_eq!(RenderLayers::layer(0).0, 1, "layer 0 is mask 1");
+        assert_eq!(RenderLayers::layer(1).0, 2, "layer 1 is mask 2");
+        assert_eq!(RenderLayers::layer(0).with(1).0, 3, "layer 0 + 1 is mask 3");
+        assert!(
+            RenderLayers::layer(1).intersects(&RenderLayers::layer(1)),
+            "layers match like layers"
+        );
+        assert!(
+            RenderLayers::layer(0).intersects(&RenderLayers(1)),
+            "a layer of 0 means the mask is just 1 bit"
+        );
+
+        assert!(
+            RenderLayers::layer(0)
+                .with(3)
+                .intersects(&RenderLayers::layer(3)),
+            "a mask will match another mask containing any similar layers"
+        );
+
+        assert!(
+            RenderLayers::default().intersects(&RenderLayers::default()),
+            "default masks match each other"
+        );
+
+        assert_eq!(
+            RenderLayers::layer(0).intersects(&RenderLayers::layer(1)),
+            false,
+            "masks with differing layers do not match"
+        );
+        assert_eq!(
+            RenderLayers(0).intersects(&RenderLayers(0)),
+            false,
+            "empty masks don't match"
+        );
+        assert_eq!(
+            RenderLayers::from_layers(&[0, 2, 16, 30])
+                .iter()
+                .collect::<Vec<_>>(),
+            vec![0, 2, 16, 30],
+            "from_layers and get_layers should roundtrip"
+        );
+        assert_eq!(
+            format!("{:?}", RenderLayers::from_layers(&[0, 1, 2, 3])).as_str(),
+            "RenderLayers([0, 1, 2, 3])",
+            "Debug instance shows layers"
+        );
+        assert_eq!(
+            RenderLayers::from_layers(&[0, 1, 2]),
+            <RenderLayers as std::iter::FromIterator<Layer>>::from_iter(vec![0, 1, 2]),
+            "from_layers and from_iter are equivalent"
+        )
+    }
+}
+
 pub fn visible_entities_system(
-    mut camera_query: Query<(&Camera, &GlobalTransform, &mut VisibleEntities)>,
-    visible_query: Query<(Entity, &Visible)>,
+    mut camera_query: Query<(
+        &Camera,
+        &GlobalTransform,
+        &mut VisibleEntities,
+        Option<&RenderLayers>,
+    )>,
+    visible_query: Query<(Entity, &Visible, Option<&RenderLayers>)>,
     visible_transform_query: Query<&GlobalTransform, With<Visible>>,
 ) {
-    for (camera, camera_global_transform, mut visible_entities) in camera_query.iter_mut() {
+    for (camera, camera_global_transform, mut visible_entities, maybe_camera_mask) in
+        camera_query.iter_mut()
+    {
         visible_entities.value.clear();
         let camera_position = camera_global_transform.translation;
+        let camera_mask = maybe_camera_mask.copied().unwrap_or_default();
 
         let mut no_transform_order = 0.0;
         let mut transparent_entities = Vec::new();
-        for (entity, visible) in visible_query.iter() {
+        for (entity, visible, maybe_entity_mask) in visible_query.iter() {
             if !visible.is_visible {
                 continue;
             }
 
+            let entity_mask = maybe_entity_mask.copied().unwrap_or_default();
+            if !camera_mask.intersects(&entity_mask) {
+                continue;
+            }
+
             let order = if let Ok(global_transform) = visible_transform_query.get(entity) {
                 let position = global_transform.translation;
                 // smaller distances are sorted to lower indices by using the distance from the camera