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Fix(bg motion vectors): gate BackgroundMotionVectorsPlugin pipelines to DownlevelFlags(INDEPENDENT_BLEND) #24067

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Fix(bg motion vectors): gate BackgroundMotionVectorsPlugin pipelines to DownlevelFlags(INDEPENDENT_BLEND) #24067

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71bf772
fix(bg motion vectors): gate setting write_mask to `DownlevelFlags(IN…
kfc35 May 2, 2026
81bf1dd
fix: disable bg motion vector pipeline if lacking downlevel flag
kfc35 May 2, 2026
66cdde6
fix: move init of `PreviousViewUniforms` before check
kfc35 May 2, 2026
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34 changes: 22 additions & 12 deletions crates/bevy_core_pipeline/src/prepass/background_motion_vectors.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -24,10 +24,10 @@ use bevy_render::{
render_resource::{
binding_types::uniform_buffer, BindGroup, BindGroupEntries, BindGroupLayoutDescriptor,
BindGroupLayoutEntries, CachedRenderPipelineId, CompareFunction, DepthStencilState,
FragmentState, MultisampleState, PipelineCache, RenderPipelineDescriptor, ShaderStages,
SpecializedRenderPipeline, SpecializedRenderPipelines,
DownlevelFlags, FragmentState, MultisampleState, PipelineCache, RenderPipelineDescriptor,
ShaderStages, SpecializedRenderPipeline, SpecializedRenderPipelines,
},
renderer::RenderDevice,
renderer::{RenderAdapter, RenderDevice},
sync_component::SyncComponent,
view::{Msaa, ViewUniform, ViewUniforms},
GpuResourceAppExt, Render, RenderApp, RenderStartup, RenderSystems,
Expand Down Expand Up @@ -120,6 +120,7 @@ struct BackgroundMotionVectorsPipeline {
struct BackgroundMotionVectorsPipelineKey {
samples: u32,
normal_prepass: bool,
supports_downlevel_independent_blend: bool,
}

fn init_background_motion_vectors_pipeline(
Expand Down Expand Up @@ -151,15 +152,18 @@ impl SpecializedRenderPipeline for BackgroundMotionVectorsPipeline {

fn specialize(&self, key: Self::Key) -> RenderPipelineDescriptor {
let mut targets = prepass_target_descriptors(key.normal_prepass, true, false);
// The shader only outputs to attachment at location 1, set write mask of the other attachments to empty
// to avoid WebGPU validation error "Color target has no corresponding fragment stage output but writeMask is not zero".
for target in
targets
.iter_mut()
.enumerate()
.filter_map(|(i, t)| if i == 1 { None } else { t.as_mut() })
{
target.write_mask = bevy_render::render_resource::ColorWrites::empty();

if key.supports_downlevel_independent_blend {
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// The shader only outputs to attachment at location 1, set write mask of the other attachments to empty
// to avoid WebGPU validation error "Color target has no corresponding fragment stage output but writeMask is not zero".
for target in
targets
.iter_mut()
.enumerate()
.filter_map(|(i, t)| if i == 1 { None } else { t.as_mut() })
{
target.write_mask = bevy_render::render_resource::ColorWrites::empty();
}
}

RenderPipelineDescriptor {
Expand Down Expand Up @@ -190,6 +194,7 @@ impl SpecializedRenderPipeline for BackgroundMotionVectorsPipeline {

fn prepare_background_motion_vectors_pipelines(
mut commands: Commands,
render_adapter: Res<RenderAdapter>,
pipeline_cache: Res<PipelineCache>,
mut pipelines: ResMut<SpecializedRenderPipelines<BackgroundMotionVectorsPipeline>>,
pipeline: Res<BackgroundMotionVectorsPipeline>,
Expand All @@ -201,13 +206,18 @@ fn prepare_background_motion_vectors_pipelines(
),
>,
) {
let supports_downlevel_independent_blend = render_adapter
.get_downlevel_capabilities()
.flags
.contains(DownlevelFlags::INDEPENDENT_BLEND);
for (entity, normal_prepass, msaa) in &views {
let id = pipelines.specialize(
&pipeline_cache,
&pipeline,
BackgroundMotionVectorsPipelineKey {
samples: msaa.samples(),
normal_prepass,
supports_downlevel_independent_blend,
},
);
commands
Expand Down