[Merged by Bors] - Example showing how to use AsyncComputeTaskPool and Tasks

Cargo.toml

@@ -87,6 +87,8 @@ anyhow = "1.0"
 rand = "0.8.0"
 ron = "0.6.2"
 serde = {version = "1", features = ["derive"]}
+# Needed to poll Task examples
+futures-lite = "1.11.3"
 
 [[example]]
 name = "hello_world"
@@ -400,6 +402,11 @@ path = "examples/shader/shader_custom_material.rs"
 name = "shader_defs"
 path = "examples/shader/shader_defs.rs"
 
+# Tasks
+[[example]]
+name = "async_compute"
+path = "examples/tasks/async_compute.rs"
+
 # Tools
 [[example]]
 name = "bevymark"

examples/tasks/async_compute.rs

@@ -0,0 +1,122 @@
+use bevy::prelude::*;
+use bevy::tasks::{AsyncComputeTaskPool, Task};
+use std::time::{Instant, Duration};
+use rand::Rng;
+use std::option::Option::Some;
+use futures_lite::future;
+
+/// This example shows how to use the ecs system and the AsyncComputeTaskPool
+/// to spawn, poll, and complete tasks across systems and system ticks.
+
+// Number of cubes to spawn across the x, y, and z axis
+const NUM_CUBES: i32 = 6;
+
+// Used to tag our new entity spawned with tasks
+struct Marker;
+
+/// This system generates tasks simulating computationally intensive
+/// work that potentially spawns multiple frames/ticks. A separate
+/// system, handle_tasks, will poll the spawned tasks on subsequent
+/// frames/ticks, and use the results to spawn cubes
+fn spawn_tasks(
+    mut commands: Commands,
+    thread_pool: Res<AsyncComputeTaskPool>,
+) {
+    for x in 0 ..NUM_CUBES {
+        for y in 0 ..NUM_CUBES {
+            for z in 0 ..NUM_CUBES {
+
+                // Spawn new task on the AsyncComputeTaskPool
+                let task = thread_pool.spawn(async move {
+
+                    let mut rng = rand::thread_rng();
+                    let start_time = Instant::now();
+                    let duration = Duration::from_secs_f32(rng.gen_range(0.05..0.2));
+                    while Instant::now() - start_time < duration {
+                        // Simulating doing hard compute work generating translation coords!
+                    }
+
+                    // Such hard work, all done!
+                    eprintln!("Done generating translation coords x: {} y: {} z: {}", x, y, z);
+                    Transform::from_translation(Vec3::new(x as f32, y as f32, z as f32))
+                });
+
+                // Spawn new entity, tag it with Marker as a component,
+                // and add our new task as a component
+                commands.spawn()
+                    .insert(Marker)
+                    .insert(task);
+            }
+        }
+    }
+}
+
+/// This system queries for entities that have both our Marker component
+/// as well as a Task<Transform> component. It polls the tasks to see if they're
+/// complete. If the task is complete it takes the result, adds a new PbrBundle of components to the
+/// entity using the result from the task's work, and removes the task component from the entity.
+fn handle_tasks(
+    mut commands: Commands,
+    mut meshes: ResMut<Assets<Mesh>>,
+    mut materials: ResMut<Assets<StandardMaterial>>,
+    mut our_entity_tasks: Query<(Entity, &mut Task<Transform>), With<Marker>>
+) {
+    for (entity, mut task) in our_entity_tasks.iter_mut() {
+
+        if let Some(transform) = future::block_on(future::poll_once(&mut *task)) {
+
+            // Normally we would add our mesh and material assets once
+            // and store the handle, but that's for another example
+            let box_mesh = meshes.add(Mesh::from(shape::Cube { size: 0.25 }));
+            let box_material = materials.add(Color::rgb(1.0, 0.2, 0.3).into());
+
+            // Add our new PbrBundle of components to our tagged entity
+            commands.entity(entity).insert_bundle(PbrBundle {
+                mesh: box_mesh.clone(),
+                material: box_material.clone(),
+                transform,
+                ..Default::default()
+            });
+
+            // Task is complete, so remove task component from entity
+            commands.entity(entity).remove::<Task<Transform>>();
+        }
+    }
+}
+
+fn main() {
+    App::build()
+        .insert_resource(Msaa { samples: 4 })
+        .add_plugins(DefaultPlugins)
+        .add_startup_system(setup_env.system())
+        .add_startup_system(spawn_tasks.system())
+        .add_system(handle_tasks.system())
+        .run();
+}
+
+/// This system IS NOT part of the example, it's only
+/// used to setup the light and camera for the environment
+fn setup_env(mut commands: Commands) {
+
+    // Used to center camera on spawned cubes
+    let offset = || {
+        if NUM_CUBES % 2 == 0 {
+            (NUM_CUBES / 2) as f32 - 0.5
+        } else {
+            (NUM_CUBES / 2) as f32
+        }
+    };
+
+    // lights
+    commands.spawn_bundle(PointLightBundle {
+        transform: Transform::from_translation(Vec3::new(4.0, 12.0, 15.0)),
+        ..Default::default()
+    });
+
+    // camera
+    commands.spawn_bundle(PerspectiveCameraBundle {
+        transform: Transform::from_translation(Vec3::new(offset(), offset(), 15.0))
+            .looking_at(Vec3::new(offset(), offset(), 0.0), Vec3::Y),
+        ..Default::default()
+    });
+}