Directional light (bevyengine#2112)

This PR adds a `DirectionalLight` component to bevy_pbr.

crates/bevy_pbr/src/lib.rs

@@ -10,7 +10,11 @@ pub use material::*;
 
 pub mod prelude {
     #[doc(hidden)]
-    pub use crate::{entity::*, light::PointLight, material::StandardMaterial};
+    pub use crate::{
+        entity::*,
+        light::{DirectionalLight, PointLight},
+        material::StandardMaterial,
+    };
 }
 
 use bevy_app::prelude::*;

crates/bevy_pbr/src/light.rs

@@ -1,11 +1,12 @@
 use bevy_core::Byteable;
 use bevy_ecs::reflect::ReflectComponent;
+use bevy_math::Vec3;
 use bevy_reflect::Reflect;
 use bevy_render::color::Color;
 use bevy_transform::components::GlobalTransform;
 
 /// A point light
-#[derive(Debug, Reflect)]
+#[derive(Debug, Clone, Copy, Reflect)]
 #[reflect(Component)]
 pub struct PointLight {
     pub color: Color,
@@ -37,7 +38,7 @@ pub(crate) struct PointLightUniform {
 unsafe impl Byteable for PointLightUniform {}
 
 impl PointLightUniform {
-    pub fn from(light: &PointLight, global_transform: &GlobalTransform) -> PointLightUniform {
+    pub fn new(light: &PointLight, global_transform: &GlobalTransform) -> PointLightUniform {
         let (x, y, z) = global_transform.translation.into();
 
         // premultiply color by intensity
@@ -52,6 +53,109 @@ impl PointLightUniform {
     }
 }
 
+/// A Directional light.
+///
+/// Directional lights don't exist in reality but they are a good
+/// approximation for light sources VERY far away, like the sun or
+/// the moon.
+///
+/// Valid values for `illuminance` are:
+///
+/// | Illuminance (lux) | Surfaces illuminated by                        |
+/// |-------------------|------------------------------------------------|
+/// | 0.0001            | Moonless, overcast night sky (starlight)       |
+/// | 0.002             | Moonless clear night sky with airglow          |
+/// | 0.05–0.3          | Full moon on a clear night                     |
+/// | 3.4               | Dark limit of civil twilight under a clear sky |
+/// | 20–50             | Public areas with dark surroundings            |
+/// | 50                | Family living room lights                      |
+/// | 80                | Office building hallway/toilet lighting        |
+/// | 100               | Very dark overcast day                         |
+/// | 150               | Train station platforms                        |
+/// | 320–500           | Office lighting                                |
+/// | 400               | Sunrise or sunset on a clear day.              |
+/// | 1000              | Overcast day; typical TV studio lighting       |
+/// | 10,000–25,000     | Full daylight (not direct sun)                 |
+/// | 32,000–100,000    | Direct sunlight                                |
+///
+/// Source: [Wikipedia](https://en.wikipedia.org/wiki/Lux)
+#[derive(Debug, Clone, Copy, Reflect)]
+#[reflect(Component)]
+pub struct DirectionalLight {
+    pub color: Color,
+    pub illuminance: f32,
+    direction: Vec3,
+}
+
+impl DirectionalLight {
+    /// Create a new directional light component.
+    pub fn new(color: Color, illuminance: f32, direction: Vec3) -> Self {
+        DirectionalLight {
+            color,
+            illuminance,
+            direction: direction.normalize(),
+        }
+    }
+
+    /// Set direction of light.
+    pub fn set_direction(&mut self, direction: Vec3) {
+        self.direction = direction.normalize();
+    }
+
+    pub fn get_direction(&self) -> Vec3 {
+        self.direction
+    }
+}
+
+impl Default for DirectionalLight {
+    fn default() -> Self {
+        DirectionalLight {
+            color: Color::rgb(1.0, 1.0, 1.0),
+            illuminance: 100000.0,
+            direction: Vec3::new(0.0, -1.0, 0.0),
+        }
+    }
+}
+
+#[repr(C)]
+#[derive(Debug, Clone, Copy)]
+pub(crate) struct DirectionalLightUniform {
+    pub dir: [f32; 4],
+    pub color: [f32; 4],
+}
+
+unsafe impl Byteable for DirectionalLightUniform {}
+
+impl DirectionalLightUniform {
+    pub fn new(light: &DirectionalLight) -> DirectionalLightUniform {
+        // direction is negated to be ready for N.L
+        let dir: [f32; 4] = [
+            -light.direction.x,
+            -light.direction.y,
+            -light.direction.z,
+            0.0,
+        ];
+
+        // convert from illuminance (lux) to candelas
+        //
+        // exposure is hard coded at the moment but should be replaced
+        // by values coming from the camera
+        // see: https://google.github.io/filament/Filament.html#imagingpipeline/physicallybasedcamera/exposuresettings
+        const APERTURE: f32 = 4.0;
+        const SHUTTER_SPEED: f32 = 1.0 / 250.0;
+        const SENSITIVITY: f32 = 100.0;
+        let ev100 = f32::log2(APERTURE * APERTURE / SHUTTER_SPEED) - f32::log2(SENSITIVITY / 100.0);
+        let exposure = 1.0 / (f32::powf(2.0, ev100) * 1.2);
+        let intensity = light.illuminance * exposure;
+
+        // premultiply color by intensity
+        // we don't use the alpha at all, so no reason to multiply only [0..3]
+        let color: [f32; 4] = (light.color * intensity).into();
+
+        DirectionalLightUniform { dir, color }
+    }
+}
+
 // Ambient light color.
 #[derive(Debug)]
 pub struct AmbientLight {

crates/bevy_pbr/src/render_graph/lights_node.rs

@@ -1,5 +1,7 @@
 use crate::{
-    light::{AmbientLight, PointLight, PointLightUniform},
+    light::{
+        AmbientLight, DirectionalLight, DirectionalLightUniform, PointLight, PointLightUniform,
+    },
     render_graph::uniform,
 };
 use bevy_core::{AsBytes, Byteable};
@@ -21,12 +23,14 @@ use bevy_transform::prelude::*;
 pub struct LightsNode {
     command_queue: CommandQueue,
     max_point_lights: usize,
+    max_dir_lights: usize,
 }
 
 impl LightsNode {
-    pub fn new(max_lights: usize) -> Self {
+    pub fn new(max_point_lights: usize, max_dir_lights: usize) -> Self {
         LightsNode {
-            max_point_lights: max_lights,
+            max_point_lights,
+            max_dir_lights,
             command_queue: CommandQueue::default(),
         }
     }
@@ -48,6 +52,8 @@ impl Node for LightsNode {
 #[derive(Debug, Clone, Copy)]
 struct LightCount {
     // storing as a `[u32; 4]` for memory alignement
+    // Index 0 is for point lights,
+    // Index 1 is for directional lights
     pub num_lights: [u32; 4],
 }
 
@@ -59,6 +65,7 @@ impl SystemNode for LightsNode {
             config.0 = Some(LightsNodeSystemState {
                 command_queue: self.command_queue.clone(),
                 max_point_lights: self.max_point_lights,
+                max_dir_lights: self.max_dir_lights,
                 light_buffer: None,
                 staging_buffer: None,
             })
@@ -74,6 +81,7 @@ pub struct LightsNodeSystemState {
     staging_buffer: Option<BufferId>,
     command_queue: CommandQueue,
     max_point_lights: usize,
+    max_dir_lights: usize,
 }
 
 pub fn lights_node_system(
@@ -83,7 +91,8 @@ pub fn lights_node_system(
     // TODO: this write on RenderResourceBindings will prevent this system from running in parallel
     // with other systems that do the same
     mut render_resource_bindings: ResMut<RenderResourceBindings>,
-    query: Query<(&PointLight, &GlobalTransform)>,
+    point_lights: Query<(&PointLight, &GlobalTransform)>,
+    dir_lights: Query<&DirectionalLight>,
 ) {
     let state = &mut state;
     let render_resource_context = &**render_resource_context;
@@ -92,16 +101,31 @@ pub fn lights_node_system(
     let ambient_light: [f32; 4] =
         (ambient_light_resource.color * ambient_light_resource.brightness).into();
     let ambient_light_size = std::mem::size_of::<[f32; 4]>();
-    let point_light_count = query.iter().len().min(state.max_point_lights);
-    let size = std::mem::size_of::<PointLightUniform>();
+
+    let point_light_count = point_lights.iter().len().min(state.max_point_lights);
+    let point_light_size = std::mem::size_of::<PointLightUniform>();
+    let point_light_array_size = point_light_size * point_light_count;
+    let point_light_array_max_size = point_light_size * state.max_point_lights;
+
+    let dir_light_count = dir_lights.iter().len().min(state.max_dir_lights);
+    let dir_light_size = std::mem::size_of::<DirectionalLightUniform>();
+    let dir_light_array_size = dir_light_size * dir_light_count;
+    let dir_light_array_max_size = dir_light_size * state.max_dir_lights;
+
     let light_count_size = ambient_light_size + std::mem::size_of::<LightCount>();
-    let point_light_array_size = size * point_light_count;
-    let point_light_array_max_size = size * state.max_point_lights;
-    let current_point_light_uniform_size = light_count_size + point_light_array_size;
-    let max_light_uniform_size = light_count_size + point_light_array_max_size;
+
+    let point_light_uniform_start = light_count_size;
+    let point_light_uniform_end = light_count_size + point_light_array_size;
+
+    let dir_light_uniform_start = light_count_size + point_light_array_max_size;
+    let dir_light_uniform_end =
+        light_count_size + point_light_array_max_size + dir_light_array_size;
+
+    let max_light_uniform_size =
+        light_count_size + point_light_array_max_size + dir_light_array_max_size;
 
     if let Some(staging_buffer) = state.staging_buffer {
-        if point_light_count == 0 {
+        if point_light_count == 0 && dir_light_count == 0 {
             return;
         }
 
@@ -133,23 +157,33 @@ pub fn lights_node_system(
     let staging_buffer = state.staging_buffer.unwrap();
     render_resource_context.write_mapped_buffer(
         staging_buffer,
-        0..current_point_light_uniform_size as u64,
+        0..max_light_uniform_size as u64,
         &mut |data, _renderer| {
             // ambient light
             data[0..ambient_light_size].copy_from_slice(ambient_light.as_bytes());
 
             // light count
-            data[ambient_light_size..light_count_size]
-                .copy_from_slice([point_light_count as u32, 0, 0, 0].as_bytes());
+            data[ambient_light_size..light_count_size].copy_from_slice(
+                [point_light_count as u32, dir_light_count as u32, 0, 0].as_bytes(),
+            );
 
-            // light array
-            for ((point_light, global_transform), slot) in query.iter().zip(
-                data[light_count_size..current_point_light_uniform_size].chunks_exact_mut(size),
+            // point light array
+            for ((point_light, global_transform), slot) in point_lights.iter().zip(
+                data[point_light_uniform_start..point_light_uniform_end]
+                    .chunks_exact_mut(point_light_size),
             ) {
                 slot.copy_from_slice(
-                    PointLightUniform::from(&point_light, &global_transform).as_bytes(),
+                    PointLightUniform::new(&point_light, &global_transform).as_bytes(),
                 );
             }
+
+            // directional light array
+            for (dir_light, slot) in dir_lights.iter().zip(
+                data[dir_light_uniform_start..dir_light_uniform_end]
+                    .chunks_exact_mut(dir_light_size),
+            ) {
+                slot.copy_from_slice(DirectionalLightUniform::new(&dir_light).as_bytes());
+            }
         },
     );
     render_resource_context.unmap_buffer(staging_buffer);

crates/bevy_pbr/src/render_graph/mod.rs

@@ -27,6 +27,7 @@ use bevy_render::{
 use bevy_transform::prelude::GlobalTransform;
 
 pub const MAX_POINT_LIGHTS: usize = 10;
+pub const MAX_DIRECTIONAL_LIGHTS: usize = 1;
 pub(crate) fn add_pbr_graph(world: &mut World) {
     {
         let mut graph = world.get_resource_mut::<RenderGraph>().unwrap();
@@ -39,7 +40,10 @@ pub(crate) fn add_pbr_graph(world: &mut World) {
             AssetRenderResourcesNode::<StandardMaterial>::new(true),
         );
 
-        graph.add_system_node(node::LIGHTS, LightsNode::new(MAX_POINT_LIGHTS));
+        graph.add_system_node(
+            node::LIGHTS,
+            LightsNode::new(MAX_POINT_LIGHTS, MAX_DIRECTIONAL_LIGHTS),
+        );
 
         // TODO: replace these with "autowire" groups
         graph