Fix sorted batching without indirect drawing

[issam3105]

Objective

Fix incorrect sorted batching when indirect drawing is unavailable.

While testing some glTF files on the web, I noticed transparent meshes rendering with the wrong geometry or transforms: some objects appeared duplicated or at incorrect positions. The same scenes rendered correctly on native Windows.

Disabling automatic batching for Transparent3d avoided the issue by setting AUTOMATIC_BATCHING to false, which pointed the investigation toward batching.

After investigation, the issue came from the NoIndirectDrawing path used when indirect drawing is unavailable. Different meshes could still be grouped as if indirect multi-draw was supported.

Solution

When NoIndirectDrawing is active, sorted phase items with different meshes now start a new batch set instead of using BreakBatch.

Testing

The original glTF asset that exposed the issue is confidential, but I can share it privately with maintainers if needed.

I was able to reproduce the issue natively on Windows by adding NoIndirectDrawing, which matches the path used on web when indirect drawing is unavailable. Press Space to test the NoIndirectDrawing path.

use bevy::{prelude::*, render::view::NoIndirectDrawing};

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .insert_resource(ClearColor(Color::srgb(0.48, 0.48, 0.48)))
        .add_systems(Startup, setup)
        .add_systems(Update, toggle_no_indirect_drawing)
        .run();
}

fn setup(
    mut commands: Commands,
    mut meshes: ResMut<Assets<Mesh>>,
    mut materials: ResMut<Assets<StandardMaterial>>,
) {
    let meshes = [
        meshes.add(Cuboid::new(0.55, 0.55, 0.55)),
        meshes.add(Sphere::new(0.36).mesh().uv(32, 18)),
        meshes.add(Cylinder::new(0.32, 0.68).mesh().resolution(36)),
    ];
    let material = materials.add(StandardMaterial {
        base_color: Color::srgba(0.05, 0.75, 1.0, 0.48),
        alpha_mode: AlphaMode::Blend,
        ..default()
    });

    for (mesh, position) in [
        (0, Vec3::new(-1.0, -0.35, -1.8)),
        (1, Vec3::new(0.0, -0.25, -1.35)),
        (2, Vec3::new(1.0, -0.15, -0.9)),
        (0, Vec3::new(-1.0, 0.35, -0.45)),
        (1, Vec3::new(0.0, 0.45, 0.0)),
        (2, Vec3::new(1.0, 0.55, 0.45)),
    ] {
        commands.spawn((
            Mesh3d(meshes[mesh].clone()),
            MeshMaterial3d(material.clone()),
            Transform::from_translation(position),
        ));
    }

    commands.spawn((
        DirectionalLight::default(),
        Transform::from_xyz(4.0, 6.0, 5.0).looking_at(Vec3::ZERO, Vec3::Y),
    ));

    let transform = Transform::from_xyz(0.0, 1.4, 4.4).looking_at(Vec3::ZERO, Vec3::Y);
    commands.spawn((Camera3d::default(), transform));
    commands.spawn((
        Camera3d::default(),
        Camera {
            is_active: false,
            ..default()
        },
        NoIndirectDrawing,
        transform,
    ));
}

fn toggle_no_indirect_drawing(
    keys: Res<ButtonInput<KeyCode>>,
    mut indirect: Single<&mut Camera, Without<NoIndirectDrawing>>,
    mut direct: Single<&mut Camera, With<NoIndirectDrawing>>,
) {
    if keys.just_pressed(KeyCode::Space) {
        let direct_enabled = indirect.is_active;
        indirect.is_active = !direct_enabled;
        direct.is_active = direct_enabled;
    }
}

Enregistrement.de.l.ecran.2026-06-22.142624.mp4

---

Showcase

Before this change, transparent glTF meshes on web could render with duplicated geometry or wrong transforms when automatic batching was enabled.

Enregistrement.de.l.ecran.2026-06-22.120126.mp4

After this change, the same scenes render correctly:

Enregistrement.de.l.ecran.2026-06-22.144337.mp4