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Use RenderStartup for order independent transparency #20170

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Use RenderStartup for order independent transparency #20170

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c5ebbfc
Use `RenderStartup` for OIT and make sure systems run conditionally.
andriyDev Jul 17, 2025
df6766a
Add the `OitResolvePipeline` to the `RenderStartup` migration guide.
andriyDev Jul 17, 2025
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97 changes: 57 additions & 40 deletions crates/bevy_core_pipeline/src/oit/resolve/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -18,7 +18,7 @@ use bevy_render::{
},
renderer::{RenderAdapter, RenderDevice},
view::{ExtractedView, ViewTarget, ViewUniform, ViewUniforms},
Render, RenderApp, RenderSystems,
Render, RenderApp, RenderStartup, RenderSystems,
};
use bevy_utils::default;
use tracing::warn;
Expand All @@ -34,30 +34,32 @@ pub struct OitResolvePlugin;
impl Plugin for OitResolvePlugin {
fn build(&self, app: &mut bevy_app::App) {
embedded_asset!(app, "oit_resolve.wgsl");
}

fn finish(&self, app: &mut bevy_app::App) {
let Some(render_app) = app.get_sub_app_mut(RenderApp) else {
return;
};

if !is_oit_supported(
render_app.world().resource::<RenderAdapter>(),
render_app.world().resource::<RenderDevice>(),
true,
) {
return;
}

render_app
.configure_sets(
RenderStartup,
OitSystems
.after(check_is_oit_supported)
.run_if(resource_exists::<OitSupported>),
)
.configure_sets(Render, OitSystems.run_if(resource_exists::<OitSupported>))
.add_systems(RenderStartup, check_is_oit_supported)
.add_systems(RenderStartup, init_oit_resolve_pipeline.in_set(OitSystems))
.add_systems(
Render,
(
queue_oit_resolve_pipeline.in_set(RenderSystems::Queue),
prepare_oit_resolve_bind_group.in_set(RenderSystems::PrepareBindGroups),
queue_oit_resolve_pipeline
.in_set(OitSystems)
.in_set(RenderSystems::Queue),
prepare_oit_resolve_bind_group
.in_set(OitSystems)
.in_set(RenderSystems::PrepareBindGroups),
),
)
.init_resource::<OitResolvePipeline>();
);
}
}

Expand Down Expand Up @@ -89,6 +91,25 @@ pub fn is_oit_supported(adapter: &RenderAdapter, device: &RenderDevice, warn: bo
true
}

/// System set for systems used for OIT.
#[derive(SystemSet, PartialEq, Eq, Hash, Debug, Clone)]
struct OitSystems;

/// A resource to indicate that OIT is supported.
#[derive(Resource)]
struct OitSupported;

/// A system to perform a one-time check for whether OIT is supported and insert a resource if so.
fn check_is_oit_supported(
mut commands: Commands,
render_device: Res<RenderDevice>,
render_adapter: Res<RenderAdapter>,
) {
if is_oit_supported(&render_adapter, &render_device, true) {
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It might require a bit more work, but this function is only used in one other place, I think we could instead inline it here and pipe the resource to that other place that needs to know if OIT is supported.

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I would like to make this a followup rather than blocking this here. Minimal diff is better for these refactors IMO!

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Especially in rendering code it's better to avoid sprawling changes because everyone touches everything all the time. The other usage site (mesh_view_bindings.rs) would require modifying more than one function, as you'd have to grab the OIT support state from the world and pass it around.

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Ah, right, I didn't realize it would be that complex, definitely follow up work then

commands.insert_resource(OitSupported);
}
}

/// Bind group for the OIT resolve pass.
#[derive(Resource, Deref)]
pub struct OitResolveBindGroup(pub BindGroup);
Expand All @@ -102,33 +123,29 @@ pub struct OitResolvePipeline {
pub oit_depth_bind_group_layout: BindGroupLayout,
}

impl FromWorld for OitResolvePipeline {
fn from_world(world: &mut World) -> Self {
let render_device = world.resource::<RenderDevice>();

let view_bind_group_layout = render_device.create_bind_group_layout(
"oit_resolve_bind_group_layout",
&BindGroupLayoutEntries::sequential(
ShaderStages::FRAGMENT,
(
uniform_buffer::<ViewUniform>(true),
// layers
storage_buffer_sized(false, None),
// layer ids
storage_buffer_sized(false, None),
),
pub fn init_oit_resolve_pipeline(mut commands: Commands, render_device: Res<RenderDevice>) {
let view_bind_group_layout = render_device.create_bind_group_layout(
"oit_resolve_bind_group_layout",
&BindGroupLayoutEntries::sequential(
ShaderStages::FRAGMENT,
(
uniform_buffer::<ViewUniform>(true),
// layers
storage_buffer_sized(false, None),
// layer ids
storage_buffer_sized(false, None),
),
);
),
);

let oit_depth_bind_group_layout = render_device.create_bind_group_layout(
"oit_depth_bind_group_layout",
&BindGroupLayoutEntries::single(ShaderStages::FRAGMENT, texture_depth_2d()),
);
OitResolvePipeline {
view_bind_group_layout,
oit_depth_bind_group_layout,
}
}
let oit_depth_bind_group_layout = render_device.create_bind_group_layout(
"oit_depth_bind_group_layout",
&BindGroupLayoutEntries::single(ShaderStages::FRAGMENT, texture_depth_2d()),
);
commands.insert_resource(OitResolvePipeline {
view_bind_group_layout,
oit_depth_bind_group_layout,
});
}

#[derive(Component, Deref, Clone, Copy)]
Expand Down
1 change: 1 addition & 0 deletions release-content/migration-guides/render_startup.md
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Original file line number Diff line number Diff line change
Expand Up @@ -41,6 +41,7 @@ The following are the (public) resources that are now initialized in `RenderStar
- `SpritePipeline`
- `Mesh2dPipeline`
- `BatchedInstanceBuffer<Mesh2dUniform>`
- `OitResolvePipeline`

The vast majority of cases for initializing render resources look like so (in Bevy 0.16):

Expand Down
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