Bevy Traditional Roguelike Quick-Start - 5. Laser Sumo Rave
Magic is nothing without the sparkles! The artifice! We need laser beams and confetti.
Visual Effects
Let us start with the preliminary Bundle, Event and other supporting structs and enums. Whenever this event will be triggered, effects of a certain colour and sprite will be placed on all selected tiles, and will gradually decay with time.
// graphics.rs
#[derive(Bundle)]
pub struct MagicEffect {
/// The tile position of this visual effect.
pub position: Position,
/// The sprite representing this visual effect.
pub sprite: Sprite,
pub visibility: Visibility,
/// The timers tracking when the effect appears, and how
/// long it takes to decay.
pub vfx: MagicVfx,
}
#[derive(Event)]
/// An event to place visual effects on the game board.
pub struct PlaceMagicVfx {
/// All tile positions on which a visual effect will appear.
pub targets: Vec<Position>,
/// Whether the effect appear one by one, or all at the same time.
pub sequence: EffectSequence,
/// The effect sprite.
pub effect: EffectType,
/// How long these effects take to decay.
pub decay: f32,
/// How long these effects take to appear.
pub appear: f32,
}
#[derive(Clone, Copy)]
pub enum EffectSequence {
/// All effects appear at the same time.
Simultaneous,
/// Effects appear one at a time, in a queue.
/// `duration` is how long it takes to move from one effect to the next.
Sequential { duration: f32 },
}
#[derive(Clone, Copy)]
pub enum EffectType {
HorizontalBeam,
VerticalBeam,
RedBlast,
GreenBlast,
XCross,
}
#[derive(Component)]
pub struct MagicVfx {
/// How long this effect takes to decay.
appear: Timer,
/// How long this effect takes to appear.
decay: Timer,
}
/// Get the appropriate texture from the spritesheet depending on the effect type.
pub fn get_effect_sprite(effect: &EffectType) -> usize {
match effect {
EffectType::HorizontalBeam => 15,
EffectType::VerticalBeam => 16,
EffectType::RedBlast => 14,
EffectType::GreenBlast => 13,
EffectType::XCross => 1,
}
}
There are only two systems to make, now - one to place the effects, and one to ensure they decay appropriately.
Each effect initially has its Visibility set to Hidden - if the effect is the tip of a laser beam, we want it to be displayed after the start of the laser beam, as to create a "trailing" effect.
// graphics.rs
pub fn place_magic_effects(
mut events: EventReader<PlaceMagicVfx>,
mut commands: Commands,
asset_server: Res<AssetServer>,
atlas_layout: Res<SpriteSheetAtlas>,
) {
for event in events.read() {
for (i, target) in event.targets.iter().enumerate() {
// Place effects on all positions from the event.
commands.spawn(MagicEffect {
position: *target,
sprite: Sprite {
image: asset_server.load("spritesheet.png"),
custom_size: Some(Vec2::new(64., 64.)),
texture_atlas: Some(TextureAtlas {
layout: atlas_layout.handle.clone(),
index: get_effect_sprite(&event.effect),
}),
..default()
},
visibility: Visibility::Hidden,
vfx: MagicVfx {
appear: match event.sequence {
// If simultaneous, everything appears at the same time.
EffectSequence::Simultaneous => {
Timer::from_seconds(event.appear, TimerMode::Once)
}
// Otherwise, effects gradually get increased appear timers depending on
// how far back they are in their queue.
EffectSequence::Sequential { duration } => Timer::from_seconds(
i as f32 * duration + event.appear,
TimerMode::Once,
),
},
decay: Timer::from_seconds(event.decay, TimerMode::Once),
},
});
}
}
}
Then, effects appear one by one (if sequential) or all at once (if simultaneous), and decay into 100% transparency after a delay preset by their decay timers.
// graphics.rs
pub fn decay_magic_effects(
mut commands: Commands,
mut magic_vfx: Query<(Entity, &mut Visibility, &mut MagicVfx, &mut Sprite)>,
time: Res<Time>,
) {
for (vfx_entity, mut vfx_vis, mut vfx_timers, mut vfx_sprite) in magic_vfx.iter_mut() {
// Effects that have completed their appear timer and are now visible, decay.
if matches!(*vfx_vis, Visibility::Inherited) {
vfx_timers.decay.tick(time.delta());
// Their alpha (transparency) slowly loses opacity as they decay.
vfx_sprite
.color
.set_alpha(vfx_timers.decay.fraction_remaining());
if vfx_timers.decay.finished() {
commands.entity(vfx_entity).despawn();
}
// Effects that have not appeared yet progress towards appearing for the first time.
} else {
vfx_timers.appear.tick(time.delta());
if vfx_timers.appear.finished() {
*vfx_vis = Visibility::Inherited;
}
}
}
}
All we need now is to properly place these effects as a result of casting spells.
// spells.rs
/// Target the caster's tile.
fn axiom_form_ego(
mut magic_vfx: EventWriter<PlaceMagicVfx>, // NEW!
mut spell_stack: ResMut<SpellStack>,
position: Query<&Position>,
) {
// Get the currently executed spell.
let synapse_data = spell_stack.spells.last_mut().unwrap();
// Get the caster's position.
let caster_position = *position.get(synapse_data.caster).unwrap();
// NEW!
// Place the visual effect.
magic_vfx.send(PlaceMagicVfx {
targets: vec![caster_position],
sequence: EffectSequence::Sequential { duration: 0.04 },
effect: EffectType::RedBlast,
decay: 0.5,
appear: 0.,
});
// End NEW.
// Add that caster's position to the targets.
synapse_data.targets.push(caster_position);
}
// spells.rs
/// Fire a beam from the caster, towards the caster's last move. Target all travelled tiles,
/// including the first solid tile encountered, which stops the beam.
fn axiom_form_momentum_beam(
mut magic_vfx: EventWriter<PlaceMagicVfx>, // NEW!
map: Res<Map>,
mut spell_stack: ResMut<SpellStack>,
position_and_momentum: Query<(&Position, &OrdDir)>,
) {
let synapse_data = spell_stack.spells.last_mut().unwrap();
let (caster_position, caster_momentum) =
position_and_momentum.get(synapse_data.caster).unwrap();
// Start the beam where the caster is standing.
// The beam travels in the direction of the caster's last move.
let (off_x, off_y) = caster_momentum.as_offset();
let mut output = linear_beam(*caster_position, 10, off_x, off_y, &map);
// NEW!
// Add some visual beam effects.
magic_vfx.send(PlaceMagicVfx {
targets: output.clone(),
sequence: EffectSequence::Sequential { duration: 0.04 },
effect: match caster_momentum {
OrdDir::Up | OrdDir::Down => EffectType::VerticalBeam,
OrdDir::Right | OrdDir::Left => EffectType::HorizontalBeam,
},
decay: 0.5,
appear: 0.,
});
// End NEW.
// Add these tiles to `targets`.
synapse_data.targets.append(&mut output);
}
If you cargo run now, you'll run into an amusing bug - the laser beams create invisible walls. This is because register_creatures cannot make the difference between a creature and a magic effect - they both have the Position component! It thinks lasers are creatures, and adds them to the Map. Let us filter them out.
// map.rs
/// Newly spawned creatures earn their place in the HashMap.
fn register_creatures(
mut map: ResMut<Map>,
// Any entity that has a Position that just got added to it -
// currently only possible as a result of having just been spawned in.
// CHANGED - Added Without<MagicVfx>
displaced_creatures: Query<(&Position, Entity), (Added<Position>, Without<MagicVfx>)>,
) {
for (position, entity) in displaced_creatures.iter() {
// Insert the new creature in the Map. Position implements Copy,
// so it can be dereferenced (*), but `.clone()` would have been
// fine too.
map.creatures.insert(*position, entity);
}
}
Don't forget to register.
// graphics.rs
impl Plugin for GraphicsPlugin {
fn build(&self, app: &mut App) {
app.init_resource::<SpriteSheetAtlas>();
app.add_systems(Startup, setup_camera);
app.add_systems(Update, adjust_transforms);
// NEW!
app.add_systems(Update, place_magic_effects);
app.add_systems(Update, decay_magic_effects);
app.add_event::<PlaceMagicVfx>();
// End NEW.
}
}
All done! cargo run, and enjoy the fireworks.
Motion Animations
All fun and good, but the instant-teleports don't fit in with all this aesthetic superiority we have just implemented. Let us fix that.
Whenever a creature teleports, it will instead interpolate its Transform translation from its origin to its destination. To do so, we'll need to rewrite adjust_transforms.
// graphics.rs
#[derive(Component)]
pub struct SlideAnimation;
/// Each frame, adjust every entity's display location to match
/// their position on the grid, and make the camera follow the player.
pub fn adjust_transforms(
mut creatures: Query<(
Entity, // NEW!
&Position,
&mut Transform,
Has<SlideAnimation>, // NEW!
Has<Player>,
)>,
mut camera: Query<&mut Transform, (With<Camera>, Without<Position>)>,
time: Res<Time>, // NEW!
mut commands: Commands, // NEW!
) {
// NEW!
for (entity, pos, mut trans, is_animated, is_player) in creatures.iter_mut() {
// If this creature is affected by an animation...
if is_animated {
// The sprite approaches its destination.
let current_translation = trans.translation;
let target_translation = Vec3::new(pos.x as f32 * 64., pos.y as f32 * 64., 0.);
// The creature is more than 0.5 pixels away from its destination - smooth animation.
if ((target_translation.x - current_translation.x).abs()
+ (target_translation.y - current_translation.y).abs())
> 0.5
{
trans.translation = trans
.translation
.lerp(target_translation, 10. * time.delta_secs());
// Otherwise, the animation is over - clip the creature onto the grid.
} else {
commands.entity(entity).remove::<SlideAnimation>();
}
} else {
// End NEW.
// For creatures with no animation.
// Multiplied by the graphical size of a tile, which is 64x64.
trans.translation.x = pos.x as f32 * 64.;
trans.translation.y = pos.y as f32 * 64.;
}
if is_player {
// The camera follows the player.
let mut camera_trans = camera.get_single_mut().unwrap();
(camera_trans.translation.x, camera_trans.translation.y) =
(trans.translation.x, trans.translation.y);
}
}
}
Creatures have their translation interpolate (lerp) towards their target translation, until the animation completes and the component responsible for orchestrating this (SlideAnimation) is removed.
Great, now, any creature with the new SlideAnimation component will gracefully make its way to its destination. Let us add that component each time a creature teleports.
// events.rs
fn teleport_entity(
mut events: EventReader<TeleportEntity>,
mut creature: Query<&mut Position>,
mut map: ResMut<Map>,
mut commands: Commands, // NEW!
) {
for event in events.read() {
// SNIP
// If motion is possible...
if map.is_passable(event.destination.x, event.destination.y) {
// SNIP
creature_position.update(event.destination.x, event.destination.y);
// Also, animate this creature, making its teleport action visible on the screen.
commands.entity(event.entity).insert(SlideAnimation); // NEW!
} else {
// Nothing here just yet, but this is where collisions between creatures
// will be handled.
continue;
}
}
}
cargo run, and your two caged creatures may have developed a little bit of sliding grace, as shown below.
Wait... why "may"? Indeed, should you restart the game multiple times, you might notice that it sometimes works, and sometimes doesn't.
Oh heavens, the worse type of bug - the non-deterministic error! How will we ever solve this? Is it time to give up?
No. We simply have not scheduled our systems.
System Scheduling
Marking systems as Update only means they trigger every tick. In which order they trigger, however, that's fully up to chance! This causes a dizzying amount of non-deterministic bugs.
To prevent this, we must tell Bevy in which order all our events and animations are handled. As a starting point, let us diagnose just how bad it has gotten.
// main.rs
fn main() {
App::new()
.add_plugins(DefaultPlugins.set(ImagePlugin::default_nearest()))
// SNIP
// NEW!
.edit_schedule(Update, |schedule| {
schedule.set_build_settings(ScheduleBuildSettings {
ambiguity_detection: LogLevel::Warn,
..default()
});
})
// End NEW.
.run();
}
You should obtain this ominous message:
7 pairs of systems with conflicting data access have indeterminate execution order. Consider adding `before`, `after`, or `ambiguous_with` relationships between these:
-- adjust_transforms and teleport_entity
conflict on: ["redesign_tgfp::map::Position"]
-- teleport_entity and player_step
conflict on: ["bevy_ecs::event::Events<redesign_tgfp::events::TeleportEntity>", "redesign_tgfp::map::Map", "redesign_tgfp::map::Position"]
-- teleport_entity and register_creatures
conflict on: ["redesign_tgfp::map::Map", "redesign_tgfp::map::Position"]
-- keyboard_input and player_step
conflict on: ["bevy_ecs::event::Events<redesign_tgfp::events::PlayerStep>"]
-- keyboard_input and cast_new_spell
conflict on: ["bevy_ecs::event::Events<redesign_tgfp::spells::CastSpell>"]
-- player_step and register_creatures
conflict on: ["redesign_tgfp::map::Map"]
-- process_axiom and cast_new_spell
conflict on: ["redesign_tgfp::spells::SpellStack"]
All of these are systems where at least one of the two modifies a certain component, leading the other system to behave completely differently depending on whether it runs before or after.
Let's bring on board a grand overseer to resolve all of these inconsistencies. Create the file sets.rs, in which a new plugin will take shape.
// sets.rs
use bevy::prelude::*;
pub struct SetsPlugin;
impl Plugin for SetsPlugin {
fn build(&self, app: &mut App) {
app.add_systems(
Update,
((
keyboard_input.run_if(spell_stack_is_empty),
creature_step,
cast_new_spell,
process_axiom,
)
.in_set(ActionPhase),
);
app.add_systems(
Update,
((register_creatures, teleport_entity).chain()).in_set(ResolutionPhase),
);
app.add_systems(
Update,
((place_magic_effects, adjust_transforms, decay_magic_effects).chain())
.in_set(AnimationPhase),
);
app.configure_sets(
Update,
(ActionPhase, AnimationPhase, ResolutionPhase).chain(),
);
}
}
#[derive(SystemSet, Debug, Clone, PartialEq, Eq, Hash)]
struct ActionPhase;
#[derive(SystemSet, Debug, Clone, PartialEq, Eq, Hash)]
struct ResolutionPhase;
#[derive(SystemSet, Debug, Clone, PartialEq, Eq, Hash)]
struct AnimationPhase;
// spells.rs
pub fn spell_stack_is_empty(spell_stack: Res<SpellStack>) -> bool {
spell_stack.spells.is_empty()
}
chain effectively means the systems run one after the other. First, I place everything related to making choices and casting spells into ActionPhase, then everything related to gameplay actions in ResolutionPhase, and finally put all the visuals and animations in AnimationPhase. The ordering was not chosen at random:
decay_magic_effectsgoes afteradjust_transforms, so the magical effects can snap to their tile position before starting to decay.register_creaturesgoes beforeteleport_entity, so that moving into the tile of a newly-summoned creature won't succeed due to the creature not having been registered into theMapyet.keyboard_inputis disallowed until all spells have finished executing, so the player cannot twitch-reflex their way out of an incoming beam.
Add this new Plugin to main.rs.
// main.rs
mod sets; // NEW!
fn main() {
App::new()
.add_plugins(DefaultPlugins.set(ImagePlugin::default_nearest()))
.add_plugins((
SetsPlugin, // NEW!
SpellPlugin,
EventPlugin,
GraphicsPlugin,
MapPlugin,
InputPlugin,
))
Also, remove all instance of the Update systems in other files to avoid duplicate systems.
// graphics.rs
impl Plugin for GraphicsPlugin {
fn build(&self, app: &mut App) {
app.init_resource::<SpriteSheetAtlas>();
app.add_event::<PlaceMagicVfx>();
app.add_systems(Startup, setup_camera);
// REMOVED Update systems.
}
}
// map.rs
impl Plugin for MapPlugin {
fn build(&self, app: &mut App) {
app.insert_resource(Map {
creatures: HashMap::new(),
});
app.add_systems(Startup, spawn_player);
app.add_systems(Startup, spawn_cage);
// REMOVED Update systems.
}
}
// events.rs
impl Plugin for EventPlugin {
fn build(&self, app: &mut App) {
app.add_event::<PlayerStep>();
app.add_event::<TeleportEntity>();
// REMOVED Update systems.
}
}
// spells.rs
impl Plugin for SpellPlugin {
fn build(&self, app: &mut App) {
app.add_event::<CastSpell>();
app.init_resource::<SpellStack>();
app.init_resource::<AxiomLibrary>();
// REMOVED Update systems.
}
}
// input.rs
// REMOVE all of the following.
pub struct InputPlugin;
impl Plugin for InputPlugin {
fn build(&self, app: &mut App) {
app.add_systems(Update, keyboard_input);
}
}
// main.rs
use events::EventPlugin;
use graphics::GraphicsPlugin;
// REMOVED InputPlugin.
use map::MapPlugin;
use sets::SetsPlugin;
use spells::SpellPlugin;
fn main() {
App::new()
.add_plugins(DefaultPlugins.set(ImagePlugin::default_nearest()))
.add_plugins((
SetsPlugin,
SpellPlugin,
EventPlugin,
GraphicsPlugin,
MapPlugin,
// REMOVED InputPlugin.
))
With all that done, cargo run! Note that this time around, the beam hits the wall, and then the wall is knocked back, all thanks to our system ordering.
