Struct StaticSystemParam

pub struct StaticSystemParam<'w, 's, P>(/* private fields */)
where
    P: SystemParam;

A helper for using system parameters in generic contexts

This type is a SystemParam adapter which always has Self::Item == Self (ignoring lifetimes for brevity), no matter the argument SystemParam (P) (other than that P must be 'static)

This makes it useful for having arbitrary SystemParam type arguments to function systems, or for generic types using the SystemParam derive:

use bevy_ecs::system::{SystemParam, StaticSystemParam};
#[derive(SystemParam)]
struct GenericParam<'w,'s, T: SystemParam + 'static> {
    field: StaticSystemParam<'w, 's, T>,
}
fn do_thing_generically<T: SystemParam + 'static>(t: StaticSystemParam<T>) {}

fn check_always_is_system<T: SystemParam + 'static>(){
    bevy_ecs::system::assert_is_system(do_thing_generically::<T>);
}

Note that in a real case you’d generally want additional bounds on P, for your use of the parameter to have a reason to be generic.

For example, using this would allow a type to be generic over whether a resource is accessed mutably or not, with impls being bounded on P: Deref<Target=MyType>, and P: DerefMut<Target=MyType> depending on whether the method requires mutable access or not.

The method which doesn’t use this type will not compile:

fn do_thing_generically<T: SystemParam + 'static>(t: T) {}

#[derive(SystemParam)]
struct GenericParam<'w, 's, T: SystemParam> {
    field: T,
    // Use the lifetimes in this type, or they will be unbound.
    phantom: std::marker::PhantomData<&'w &'s ()>
}

Implementations

impl<'w, 's, P> StaticSystemParam<'w, 's, P>

where P: SystemParam,

pub fn into_inner(self) -> <P as SystemParam>::Item<'w, 's>

Get the value of the parameter

Examples found in repository

examples/shader/specialized_mesh_pipeline.rs (line 300)

fn queue_custom_mesh_pipeline(
    pipeline_cache: Res<PipelineCache>,
    custom_mesh_pipeline: Res<CustomMeshPipeline>,
    (mut opaque_render_phases, opaque_draw_functions): (
        ResMut<ViewBinnedRenderPhases<Opaque3d>>,
        Res<DrawFunctions<Opaque3d>>,
    ),
    mut specialized_mesh_pipelines: ResMut<SpecializedMeshPipelines<CustomMeshPipeline>>,
    views: Query<(
        &RenderVisibleEntities,
        &ExtractedView,
        &Msaa,
        Has<NoIndirectDrawing>,
        Has<OcclusionCulling>,
    )>,
    (render_meshes, render_mesh_instances): (
        Res<RenderAssets<RenderMesh>>,
        Res<RenderMeshInstances>,
    ),
    param: StaticSystemParam<<MeshPipeline as GetBatchData>::Param>,
    mut phase_batched_instance_buffers: ResMut<
        PhaseBatchedInstanceBuffers<Opaque3d, <MeshPipeline as GetBatchData>::BufferData>,
    >,
    mut phase_indirect_parameters_buffers: ResMut<PhaseIndirectParametersBuffers<Opaque3d>>,
    mut change_tick: Local<Tick>,
) {
    let system_param_item = param.into_inner();

    let UntypedPhaseBatchedInstanceBuffers {
        ref mut data_buffer,
        ref mut work_item_buffers,
        ref mut late_indexed_indirect_parameters_buffer,
        ref mut late_non_indexed_indirect_parameters_buffer,
        ..
    } = phase_batched_instance_buffers.buffers;

    // Get the id for our custom draw function
    let draw_function_id = opaque_draw_functions
        .read()
        .id::<DrawSpecializedPipelineCommands>();

    // Render phases are per-view, so we need to iterate over all views so that
    // the entity appears in them. (In this example, we have only one view, but
    // it's good practice to loop over all views anyway.)
    for (view_visible_entities, view, msaa, no_indirect_drawing, gpu_occlusion_culling) in
        views.iter()
    {
        let Some(opaque_phase) = opaque_render_phases.get_mut(&view.retained_view_entity) else {
            continue;
        };

        // Create *work item buffers* if necessary. Work item buffers store the
        // indices of meshes that are to be rendered when indirect drawing is
        // enabled.
        let work_item_buffer = gpu_preprocessing::get_or_create_work_item_buffer::<Opaque3d>(
            work_item_buffers,
            view.retained_view_entity,
            no_indirect_drawing,
            gpu_occlusion_culling,
        );

        // Initialize those work item buffers in preparation for this new frame.
        gpu_preprocessing::init_work_item_buffers(
            work_item_buffer,
            late_indexed_indirect_parameters_buffer,
            late_non_indexed_indirect_parameters_buffer,
        );

        // Create the key based on the view. In this case we only care about MSAA and HDR
        let view_key = MeshPipelineKey::from_msaa_samples(msaa.samples())
            | MeshPipelineKey::from_hdr(view.hdr);

        // Set up a slot to hold information about the batch set we're going to
        // create. If there are any of our custom meshes in the scene, we'll
        // need this information in order for Bevy to kick off the rendering.
        let mut mesh_batch_set_info = None;

        // Find all the custom rendered entities that are visible from this
        // view.
        for &(render_entity, visible_entity) in
            view_visible_entities.get::<CustomRenderedEntity>().iter()
        {
            // Get the mesh instance
            let Some(mesh_instance) = render_mesh_instances.render_mesh_queue_data(visible_entity)
            else {
                continue;
            };

            // Get the mesh data
            let Some(mesh) = render_meshes.get(mesh_instance.mesh_asset_id) else {
                continue;
            };

            // Specialize the key for the current mesh entity
            // For this example we only specialize based on the mesh topology
            // but you could have more complex keys and that's where you'd need to create those keys
            let mut mesh_key = view_key;
            mesh_key |= MeshPipelineKey::from_primitive_topology(mesh.primitive_topology());

            // Initialize the batch set information if this was the first custom
            // mesh we saw. We'll need that information later to create the
            // batch set.
            if mesh_batch_set_info.is_none() {
                mesh_batch_set_info = Some(MeshBatchSetInfo {
                    indirect_parameters_index: phase_indirect_parameters_buffers
                        .buffers
                        .allocate(mesh.indexed(), 1),
                    is_indexed: mesh.indexed(),
                });
            }
            let mesh_info = mesh_batch_set_info.unwrap();

            // Allocate some input and output indices. We'll need these to
            // create the *work item* below.
            let Some(input_index) =
                MeshPipeline::get_binned_index(&system_param_item, visible_entity)
            else {
                continue;
            };
            let output_index = data_buffer.add() as u32;

            // Finally, we can specialize the pipeline based on the key
            let pipeline_id = specialized_mesh_pipelines
                .specialize(
                    &pipeline_cache,
                    &custom_mesh_pipeline,
                    mesh_key,
                    &mesh.layout,
                )
                // This should never with this example, but if your pipeline specialization
                // can fail you need to handle the error here
                .expect("Failed to specialize mesh pipeline");

            // Bump the change tick so that Bevy is forced to rebuild the bin.
            let next_change_tick = change_tick.get() + 1;
            change_tick.set(next_change_tick);

            // Add the mesh with our specialized pipeline
            opaque_phase.add(
                Opaque3dBatchSetKey {
                    draw_function: draw_function_id,
                    pipeline: pipeline_id,
                    material_bind_group_index: None,
                    vertex_slab: default(),
                    index_slab: None,
                    lightmap_slab: None,
                },
                // The asset ID is arbitrary; we simply use [`AssetId::invalid`],
                // but you can use anything you like. Note that the asset ID need
                // not be the ID of a [`Mesh`].
                Opaque3dBinKey {
                    asset_id: AssetId::<Mesh>::invalid().untyped(),
                },
                (render_entity, visible_entity),
                mesh_instance.current_uniform_index,
                // This example supports batching, but if your pipeline doesn't
                // support it you can use `BinnedRenderPhaseType::UnbatchableMesh`
                BinnedRenderPhaseType::BatchableMesh,
                *change_tick,
            );

            // Create a *work item*. A work item tells the Bevy renderer to
            // transform the mesh on GPU.
            work_item_buffer.push(
                mesh.indexed(),
                PreprocessWorkItem {
                    input_index: input_index.into(),
                    output_or_indirect_parameters_index: if no_indirect_drawing {
                        output_index
                    } else {
                        mesh_info.indirect_parameters_index
                    },
                },
            );
        }

        // Now if there were any meshes, we need to add a command to the
        // indirect parameters buffer, so that the renderer will end up
        // enqueuing a command to draw the mesh.
        if let Some(mesh_info) = mesh_batch_set_info {
            phase_indirect_parameters_buffers
                .buffers
                .add_batch_set(mesh_info.is_indexed, mesh_info.indirect_parameters_index);
        }
    }
}

Trait Implementations

impl<'w, 's, P> Deref for StaticSystemParam<'w, 's, P>

where P: SystemParam,

type Target = <P as SystemParam>::Item<'w, 's>

The resulting type after dereferencing.

fn deref(&self) -> &<StaticSystemParam<'w, 's, P> as Deref>::Target

Dereferences the value.

impl<'w, 's, P> DerefMut for StaticSystemParam<'w, 's, P>

where P: SystemParam,

fn deref_mut(&mut self) -> &mut <StaticSystemParam<'w, 's, P> as Deref>::Target

Mutably dereferences the value.

impl<P> SystemParam for StaticSystemParam<'_, '_, P>

where P: SystemParam + 'static,

type State = <P as SystemParam>::State

Used to store data which persists across invocations of a system.

type Item<'world, 'state> = StaticSystemParam<'world, 'state, P>

The item type returned when constructing this system param. The value of this associated type should be Self, instantiated with new lifetimes.

fn init_state( world: &mut World, system_meta: &mut SystemMeta, ) -> <StaticSystemParam<'_, '_, P> as SystemParam>::State

Registers any World access used by this SystemParam and creates a new instance of this param’s State.

unsafe fn new_archetype( state: &mut <StaticSystemParam<'_, '_, P> as SystemParam>::State, archetype: &Archetype, system_meta: &mut SystemMeta, )

For the specified Archetype, registers the components accessed by this SystemParam (if applicable).a

fn apply( state: &mut <StaticSystemParam<'_, '_, P> as SystemParam>::State, system_meta: &SystemMeta, world: &mut World, )

Applies any deferred mutations stored in this SystemParam’s state. This is used to apply Commands during ApplyDeferred.

fn queue( state: &mut <StaticSystemParam<'_, '_, P> as SystemParam>::State, system_meta: &SystemMeta, world: DeferredWorld<'_>, )

Queues any deferred mutations to be applied at the next ApplyDeferred.

unsafe fn validate_param( state: &<StaticSystemParam<'_, '_, P> as SystemParam>::State, system_meta: &SystemMeta, world: UnsafeWorldCell<'_>, ) -> Result<(), SystemParamValidationError>

Validates that the param can be acquired by the get_param.

unsafe fn get_param<'world, 'state>( state: &'state mut <StaticSystemParam<'_, '_, P> as SystemParam>::State, system_meta: &SystemMeta, world: UnsafeWorldCell<'world>, change_tick: Tick, ) -> <StaticSystemParam<'_, '_, P> as SystemParam>::Item<'world, 'state>

Creates a parameter to be passed into a SystemParamFunction.

impl<'w, 's, P> ReadOnlySystemParam for StaticSystemParam<'w, 's, P>

where P: ReadOnlySystemParam + 'static,