Use empty buffer instead of populating junk data

CHANGELOG.md

@@ -14,6 +14,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Fixed
 
 - Point lights rendering despite being despawned (#25).
+- Shadow sometimes appearing when no occluders were present (#27).
 
 ### Migration guide
 

src/plugin.rs

@@ -18,6 +18,7 @@ use crate::{
     light::{AmbientLight2d, PointLight2d},
     occluder::LightOccluder2d,
     render::{
+        empty_buffer::{prepare_empty_buffer, EmptyBuffer},
         extract::{
             extract_ambient_lights, extract_light_occluders, extract_point_lights,
             ExtractedAmbientLight2d, ExtractedLightOccluder2d, ExtractedPointLight2d,
@@ -84,6 +85,7 @@ impl Plugin for Light2dPlugin {
         render_app
             .init_resource::<SpecializedRenderPipelines<LightingPipeline>>()
             .init_resource::<PointLightMetaBuffer>()
+            .init_resource::<EmptyBuffer>()
             .add_systems(
                 ExtractSchedule,
                 (
@@ -97,6 +99,7 @@ impl Plugin for Light2dPlugin {
                 (
                     prepare_lighting_pipelines.in_set(RenderSet::Prepare),
                     prepare_point_light_count.in_set(RenderSet::Prepare),
+                    prepare_empty_buffer.in_set(RenderSet::Prepare),
                     prepare_sdf_texture
                         .after(prepare_view_targets)
                         .in_set(RenderSet::ManageViews),

src/render/empty_buffer.rs

@@ -0,0 +1,42 @@
+use bevy::{
+    ecs::system::{Res, ResMut, Resource},
+    render::{
+        render_resource::{BindingResource, Buffer, BufferDescriptor, BufferUsages},
+        renderer::RenderDevice,
+    },
+};
+
+/// A resource serving as a general purpose "empty" buffer, allowing us to use it as a
+/// stand in for times we don't have a usable binding (such as an empty array).
+#[derive(Resource, Default)]
+pub struct EmptyBuffer {
+    pub buffer: Option<Buffer>,
+}
+
+impl EmptyBuffer {
+    pub fn binding(&self) -> Option<BindingResource> {
+        self.buffer
+            .as_ref()
+            .map(|buffer| BindingResource::Buffer(buffer.as_entire_buffer_binding()))
+    }
+
+    pub fn fill_buffer(&mut self, render_device: &RenderDevice) {
+        if self.buffer.is_none() {
+            self.buffer = Some(render_device.create_buffer(&BufferDescriptor {
+                label: "empty-buffer".into(),
+                // This needs to be at least as big as the items we're storing in our
+                // GPUArrayBuffer.
+                size: 64,
+                usage: BufferUsages::COPY_DST | BufferUsages::STORAGE | BufferUsages::UNIFORM,
+                mapped_at_creation: false,
+            }));
+        }
+    }
+}
+
+pub fn prepare_empty_buffer(
+    mut empty_buffer: ResMut<EmptyBuffer>,
+    render_device: Res<RenderDevice>,
+) {
+    empty_buffer.fill_buffer(&render_device);
+}

src/render/extract.rs

@@ -46,17 +46,6 @@ pub fn extract_point_lights(
             cast_shadows: if point_light.cast_shadows { 1 } else { 0 },
         });
     }
-
-    // BufferVec won't write to the GPU if there aren't any point lights.
-    // For now we can spawn an empty point light to get around this.
-    commands.spawn(ExtractedPointLight2d {
-        transform: Vec2::ZERO,
-        intensity: 0.0,
-        radius: 0.0,
-        falloff: 0.0,
-        color: LinearRgba::BLACK,
-        cast_shadows: 0,
-    });
 }
 
 pub fn extract_light_occluders(
@@ -79,10 +68,6 @@ pub fn extract_light_occluders(
 
         commands.get_or_spawn(entity).insert(extracted_occluder);
     }
-
-    // BufferVec won't write to the GPU if there aren't any point lights.
-    // For now we can spawn an empty occluder to get around this.
-    commands.spawn(ExtractedLightOccluder2d::default());
 }
 
 pub fn extract_ambient_lights(

src/render/light_map/node.rs

@@ -11,6 +11,7 @@ use bevy::render::renderer::RenderDevice;
 use bevy::render::view::{ViewUniformOffset, ViewUniforms};
 use smallvec::{smallvec, SmallVec};
 
+use crate::render::empty_buffer::EmptyBuffer;
 use crate::render::extract::{ExtractedAmbientLight2d, ExtractedPointLight2d};
 use crate::render::sdf::SdfTexture;
 
@@ -58,7 +59,8 @@ impl ViewNode for LightMapNode {
                 .binding(),
             world
                 .resource::<GpuArrayBuffer<ExtractedPointLight2d>>()
-                .binding(),
+                .binding()
+                .or(world.resource::<EmptyBuffer>().binding()),
             world.resource::<PointLightMetaBuffer>().buffer.binding(),
         )
         else {

src/render/mod.rs

@@ -1,5 +1,6 @@
 use bevy::{asset::Handle, render::render_resource::Shader};
 
+pub mod empty_buffer;
 pub mod extract;
 pub mod light_map;
 pub mod lighting;

src/render/sdf/node.rs

@@ -10,6 +10,7 @@ use bevy::render::renderer::RenderDevice;
 use bevy::render::view::{ViewUniformOffset, ViewUniforms};
 use smallvec::{smallvec, SmallVec};
 
+use crate::render::empty_buffer::EmptyBuffer;
 use crate::render::extract::ExtractedLightOccluder2d;
 
 use super::pipeline::SdfPipeline;
@@ -39,7 +40,8 @@ impl ViewNode for SdfNode {
             world.resource::<ViewUniforms>().uniforms.binding(),
             world
                 .resource::<GpuArrayBuffer<ExtractedLightOccluder2d>>()
-                .binding(),
+                .binding()
+                .or(world.resource::<EmptyBuffer>().binding()),
         ) else {
             return Ok(());
         };