Add support for setting blending mode

[Soulghost]

This commit adds a with_blending_mode, which can be used to set the blending mode for the particle renderer. In addition to alpha blend mode, premultiply and additive mode has been added.

The additive blending mode is useful for glow effects, the picture below makes a comparison.

Additive Blending

Alpha Blending

Sample Code

//! Example of additive blend mode.
//!
//! This example demonstrate how to change the blend mode for the particle renderer.

use bevy::{
    core_pipeline::tonemapping::Tonemapping,
    log::LogPlugin,
    prelude::*,
    render::{
        camera::Projection, render_resource::WgpuFeatures, settings::WgpuSettings, RenderPlugin,
    },
};
#[cfg(feature = "examples_world_inspector")]
use bevy_inspector_egui::quick::WorldInspectorPlugin;

use bevy_hanabi::prelude::*;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let mut wgpu_settings = WgpuSettings::default();
    wgpu_settings
        .features
        .set(WgpuFeatures::VERTEX_WRITABLE_STORAGE, true);

    let mut app = App::default();
    app.insert_resource(ClearColor(Color::DARK_GRAY))
        .add_plugins(
            DefaultPlugins
                .set(LogPlugin {
                    level: bevy::log::Level::WARN,
                    filter: "bevy_hanabi=warn,additive=trace".to_string(),
                    update_subscriber: None,
                })
                .set(RenderPlugin {
                    render_creation: wgpu_settings.into(),
                    synchronous_pipeline_compilation: false,
                })
                .set(WindowPlugin {
                    primary_window: Some(Window {
                        title: "🎆 Hanabi — additive blending".to_string(),
                        ..default()
                    }),
                    ..default()
                }),
        )
        .add_plugins(HanabiPlugin);

    #[cfg(feature = "examples_world_inspector")]
    app.add_plugins(WorldInspectorPlugin::default());

    app.add_systems(Startup, setup)
        .add_systems(Update, bevy::window::close_on_esc)
        .run();

    Ok(())
}

fn setup(
    asset_server: Res<AssetServer>,
    mut commands: Commands,
    mut effects: ResMut<Assets<EffectAsset>>,
) {
    let camera = Camera3dBundle {
        transform: Transform::from_xyz(0.0, 0.0, 3.0).looking_at(Vec3::ZERO, Vec3::Y),
        projection: Projection::Perspective(PerspectiveProjection {
            fov: 90.0,
            ..Default::default()
        }),
        tonemapping: Tonemapping::None,
        ..Default::default()
    };

    commands.spawn(camera);

    let texture_handle: Handle<Image> = asset_server.load("orange_circle.png");

    let writer = ExprWriter::new();

    let age = writer.lit(0.).expr();
    let init_age = SetAttributeModifier::new(Attribute::AGE, age);

    let lifetime = writer.lit(5.).expr();
    let init_lifetime = SetAttributeModifier::new(Attribute::LIFETIME, lifetime);

    let init_pos = SetPositionCircleModifier {
        center: writer.lit(0.).expr(),
        axis: writer.lit(Vec3::Z).expr(),
        radius: writer.lit(0.2).expr(),
        dimension: ShapeDimension::Volume,
    };

    let init_vel = SetVelocityCircleModifier {
        center: writer.lit(Vec3::ZERO).expr(),
        axis: writer.lit(Vec3::Z).expr(),
        speed: (writer.lit(0.2) + writer.lit(0.2) * writer.rand(ScalarType::Float)).expr(),
    };

    // Use the F32_0 attribute as a per-particle rotation value, initialized on
    // spawn and constant after. The rotation angle is in radians, here randomly
    // selected in [0:2*PI].
    let rotation = (writer.rand(ScalarType::Float) * writer.lit(std::f32::consts::TAU)).expr();
    let init_rotation = SetAttributeModifier::new(Attribute::F32_0, rotation);

    let size = Vec2::splat(0.8);
    let effect = effects.add(
        EffectAsset::new(vec![32768], Spawner::rate(5.0.into()), writer.finish())
            .with_name("additive")
            .with_alpha_mode(bevy_hanabi::AlphaMode::Add)
            .init(init_pos)
            .init(init_vel)
            .init(init_age)
            .init(init_lifetime)
            .init(init_rotation)
            .render(ParticleTextureModifier {
                texture: texture_handle,
                sample_mapping: ImageSampleMapping::Modulate,
            })
            .render(SetSizeModifier { size: size.into() }),
    );

    commands
        .spawn(ParticleEffectBundle::new(effect))
        .insert(Name::new("effect"));
}

Add this image to the assets/orange_circle.png

[SludgePhD]

Neat, this would fix #227

[Soulghost]

Hi @djeedai , Please help me review this PR, thanks!

[djeedai]

Hi- Thanks for the PR! I'm OK in principle I think but there's a few things I'm not convinced about:

1. we do a lot of duplication here, see other comments.
2. this probably doesn't justify the overhead of maintaining a full separate example just for this, and especially adding new assets (which are shipped with the crate and increase its size, even if just for examples)

[djeedai]

@Soulghost would you mind please merge latest main to get the clippy fixes for the CI breaks ("Check format" action)? Ignore the "run-examples" failure, this is an upstream bug in wgpu it can't be fixed for now (it's fixed in Bevy 0.14).

[Soulghost]

Hi @djeedai , I have rebased my feature branch based on the latest main branch, please review my code again, thank you very much.

[Soulghost]

Hi @djeedai , it appears that the failure of run-examples and coverage/coveralls are preventing the merge process.

[djeedai]

@Soulghost don't mind those. There's no auto-merge, I make the call on whether to merge. In that case coverage drop is minimal so all fine, and the failing examples is a bug upstream we can't do anything about for now. So all good. I'll have a final look later and merge.

[Soulghost]

@Soulghost don't mind those. There's no auto-merge, I make the call on whether to merge. In that case coverage drop is minimal so all fine, and the failing examples is a bug upstream we can't do anything about for now. So all good. I'll have a final look later and merge.

Got it, thank you very much.