Add example

Cargo.toml

@@ -1577,6 +1577,17 @@ path = "tests/window/minimising.rs"
 [package.metadata.example.minimising]
 hidden = true
 
+[[example]]
+name = "virtual"
+path = "examples/window/virtual.rs"
+
+[package.metadata.example.virtual]
+name = "Virtual Window"
+description = "Demonstrates creating virtual windows and manually setting their render target"
+category = "Window"
+wasm = true
+
+
 [[example]]
 name = "window_resizing"
 path = "examples/window/window_resizing.rs"

examples/README.md

@@ -328,6 +328,7 @@ Example | Description
 [Multiple Windows](../examples/window/multiple_windows.rs) | Demonstrates creating multiple windows, and rendering to them
 [Scale Factor Override](../examples/window/scale_factor_override.rs) | Illustrates how to customize the default window settings
 [Transparent Window](../examples/window/transparent_window.rs) | Illustrates making the window transparent and hiding the window decoration
+[Virtual Window](../examples/window/virtual.rs) | Demonstrates creating virtual windows and manually setting their render target
 [Window Resizing](../examples/window/window_resizing.rs) | Demonstrates resizing and responding to resizing a window
 [Window Settings](../examples/window/window_settings.rs) | Demonstrates customizing default window settings
 

examples/window/virtual.rs

@@ -0,0 +1,211 @@
+//! Uses two windows to visualize a 3D model from different angles.
+
+use std::f32::consts::PI;
+
+use bevy::{
+    core_pipeline::clear_color::ClearColorConfig,
+    prelude::*,
+    render::{
+        camera::RenderTarget,
+        extract_resource::{ExtractResource, ExtractResourcePlugin},
+        render_asset::{PrepareAssetLabel, RenderAssets},
+        render_resource::{
+            Extent3d, TextureDescriptor, TextureDimension, TextureFormat, TextureUsages,
+        },
+        view::{ExtractedWindows, RenderLayers, WindowSystem},
+        RenderApp, RenderStage,
+    },
+    window::{PresentMode, WindowId},
+};
+
+#[derive(Clone, Resource)]
+struct WindowTexture {
+    window_id: WindowId,
+    render_texture: Handle<Image>,
+}
+
+impl ExtractResource for WindowTexture {
+    type Source = WindowTexture;
+
+    fn extract_resource(source: &WindowTexture) -> Self {
+        source.clone()
+    }
+}
+
+fn main() {
+    let mut app = App::new();
+    app.add_plugins(DefaultPlugins)
+        .add_startup_system(setup)
+        .add_system(bevy::window::close_on_esc)
+        .add_plugin(ExtractResourcePlugin::<WindowTexture>::default());
+    if let Ok(render_app) = app.get_sub_app_mut(RenderApp) {
+        render_app.add_system_to_stage(
+            RenderStage::Prepare,
+            prepare_window_texture
+                .after(PrepareAssetLabel::AssetPrepare)
+                .before(WindowSystem::Prepare),
+        );
+    }
+    app.run();
+}
+
+fn prepare_window_texture(
+    window_texture: Res<WindowTexture>,
+    gpu_images: Res<RenderAssets<Image>>,
+    mut extracted_windows: ResMut<ExtractedWindows>,
+) {
+    if let Some(window) = extracted_windows.get_mut(&window_texture.window_id) {
+        window.swap_chain_texture = Some(
+            gpu_images
+                .get(&window_texture.render_texture)
+                .unwrap()
+                .texture_view
+                .clone(),
+        );
+    }
+}
+
+fn setup(
+    mut commands: Commands,
+    mut meshes: ResMut<Assets<Mesh>>,
+    mut materials: ResMut<Assets<StandardMaterial>>,
+    mut images: ResMut<Assets<Image>>,
+    mut windows: ResMut<Windows>,
+) {
+    let window_id = WindowId::new();
+    windows.add(Window::new_virtual(
+        window_id,
+        &WindowDescriptor {
+            width: 800.,
+            height: 600.,
+            present_mode: PresentMode::AutoNoVsync,
+            title: "Second window".to_string(),
+            ..default()
+        },
+        800,
+        600,
+        1.0,
+        None,
+    ));
+
+    let size = Extent3d {
+        width: 800,
+        height: 600,
+        ..default()
+    };
+
+    // This is the texture that will be rendered to.
+    let mut image = Image {
+        texture_descriptor: TextureDescriptor {
+            label: None,
+            size,
+            dimension: TextureDimension::D2,
+            format: TextureFormat::Bgra8UnormSrgb,
+            mip_level_count: 1,
+            sample_count: 1,
+            usage: TextureUsages::TEXTURE_BINDING
+                | TextureUsages::COPY_DST
+                | TextureUsages::RENDER_ATTACHMENT,
+        },
+        ..default()
+    };
+
+    // fill image.data with zeroes
+    image.resize(size);
+
+    let image_handle = images.add(image);
+    commands.insert_resource(WindowTexture {
+        window_id,
+        render_texture: image_handle.clone(),
+    });
+
+    let cube_handle = meshes.add(Mesh::from(shape::Cube { size: 4.0 }));
+    let cube_material_handle = materials.add(StandardMaterial {
+        base_color: Color::rgb(0.8, 0.7, 0.6),
+        reflectance: 0.02,
+        unlit: false,
+        ..default()
+    });
+
+    // This specifies the layer used for the first pass, which will be attached to the first pass camera and cube.
+    let first_pass_layer = RenderLayers::layer(1);
+
+    // The cube that will be rendered to the texture.
+    commands.spawn((
+        PbrBundle {
+            mesh: cube_handle,
+            material: cube_material_handle,
+            transform: Transform::from_translation(Vec3::new(0.0, 0.0, 1.0)),
+            ..default()
+        },
+        first_pass_layer,
+    ));
+
+    // Light
+    // NOTE: Currently lights are shared between passes - see https://github.com/bevyengine/bevy/issues/3462
+    commands.spawn(PointLightBundle {
+        transform: Transform::from_translation(Vec3::new(0.0, 0.0, 10.0)),
+        ..default()
+    });
+
+    commands.spawn((
+        Camera3dBundle {
+            camera_3d: Camera3d {
+                clear_color: ClearColorConfig::Custom(Color::WHITE),
+                ..default()
+            },
+            camera: Camera {
+                // render before the "main pass" camera
+                priority: -1,
+                target: RenderTarget::Image(image_handle.clone()),
+                ..default()
+            },
+            transform: Transform::from_translation(Vec3::new(0.0, 0.0, 15.0))
+                .looking_at(Vec3::ZERO, Vec3::Y),
+            ..default()
+        },
+        first_pass_layer,
+    ));
+
+    let cube_size = 4.0;
+    let cube_handle = meshes.add(Mesh::from(shape::Box::new(cube_size, cube_size, cube_size)));
+
+    // This material has the texture that has been rendered.
+    let material_handle = materials.add(StandardMaterial {
+        base_color_texture: Some(image_handle),
+        reflectance: 0.02,
+        unlit: false,
+        ..default()
+    });
+
+    // Main pass cube, with material containing the rendered first pass texture.
+    commands.spawn(PbrBundle {
+        mesh: cube_handle,
+        material: material_handle,
+        transform: Transform::from_xyz(0.0, 0.0, 1.5)
+            .with_rotation(Quat::from_rotation_x(-PI / 5.0)),
+        ..default()
+    });
+
+    // The main pass camera.
+    commands.spawn(Camera3dBundle {
+        transform: Transform::from_xyz(0.0, 0.0, 15.0).looking_at(Vec3::ZERO, Vec3::Y),
+        ..default()
+    });
+
+    let window_id = WindowId::new();
+    windows.add(Window::new_virtual(
+        window_id,
+        &WindowDescriptor {
+            width: 800.,
+            height: 600.,
+            present_mode: PresentMode::AutoNoVsync,
+            title: "Second window".to_string(),
+            ..default()
+        },
+        800,
+        600,
+        1.0,
+        None,
+    ));
+}