Saving RenderTarget image data to a file

[Isso4820]

Now that in Bevy 0.8 it's possible to render to a texture I was wondering if this could be used to generate screen captures (resolve #1207).

I've attempted this with following code. Unfortunately, it doesn't work and I always get an empty image.

use bevy::{
    prelude::*,
    render::{
        camera::RenderTarget,
        render_resource::{
            Extent3d, TextureDescriptor, TextureDimension, TextureFormat, TextureUsages,
        },
    }
};
use std::fs;

#[derive(Component)]
struct ScreenTextureMarker;

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_startup_system(setup)
        .add_system(query)
        .run();
}

fn setup(
    mut commands: Commands,
    mut meshes: ResMut<Assets<Mesh>>,
    mut materials: ResMut<Assets<StandardMaterial>>,
    mut images: ResMut<Assets<Image>>,
) {
    let size = Extent3d {
        width: 512,
        height: 512,
        depth_or_array_layers: 1,
    };

    // 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);

    // plane
    commands.spawn_bundle(PbrBundle {
        mesh: meshes.add(Mesh::from(shape::Plane { size: 5.0 })),
        material: materials.add(Color::rgb(0.3, 0.5, 0.3).into()),
        ..default()
    });
    // cube
    commands.spawn_bundle(PbrBundle {
        mesh: meshes.add(Mesh::from(shape::Cube { size: 1.0 })),
        material: materials.add(Color::rgb(0.8, 0.7, 0.6).into()),
        transform: Transform::from_xyz(0.0, 0.5, 0.0),
        ..default()
    });
    // light
    commands.spawn_bundle(PointLightBundle {
        point_light: PointLight {
            intensity: 1500.0,
            shadows_enabled: true,
            ..default()
        },
        transform: Transform::from_xyz(4.0, 8.0, 4.0),
        ..default()
    });
    // camera with texture as render target
    commands.spawn_bundle(Camera3dBundle {
        transform: Transform::from_xyz(-2.0, 2.5, 5.0).looking_at(Vec3::ZERO, Vec3::Y),
        camera: Camera {
            target: RenderTarget::Image(image_handle.clone()),
            ..default()
        },
        ..default()
    });
    // normal camera
    commands.spawn_bundle(Camera3dBundle {
        transform: Transform::from_xyz(-2.0, 2.5, 5.0).looking_at(Vec3::ZERO, Vec3::Y),
        camera: Camera {
            ..default()
        },
        ..default()
    });

    commands.spawn().insert(image_handle.clone()).insert(ScreenTextureMarker);
}

fn query(
    keyboard_input: Res<Input<KeyCode>>,
    images: Res<Assets<Image>>,
    screen_texture: Query<(&ScreenTextureMarker, &Handle<Image>)>
) {
    if keyboard_input.just_released(KeyCode::Space) {
        println!("Attempt to take a screenshot");
        for (_, handle) in &screen_texture {
            if let Some(image) = images.get(handle) {
                // trying to read with convert -depth 8 -size 512x512 RGBA:image test.png
                fs::write("/tmp/image", &image.data).expect("Unable to write file");
            } else {
                println!("Not found");
            }
        }
    }
}

What am I doing wrong?

[kezuo]

Maybe the data of the image is still in gpu，it need be copied back to cpu。
https://github.com/bevyengine/bevy/pull/5550/files

[WannaBeKratos]

Having the same issue, is this not possible with bevy ?

[paulkre]

Check out the bevy_image_export plugin.