Enemy Spawn Example

This example demonstrates the spawn system with timed enemy spawning, object pooling, and movement behaviors using the helios game loop architecture with typed passes and state management.

Features

• GameLoop Architecture - Phase-based game loop with Pre/Main/Post phases, typed passes, and commit points
• SpawnSystemFactory DSL - Declarative spawn configuration with fluent builder API
• Object Pooling - Efficient enemy management via GameObjectPoolManager with PrefabId
• Random Placement - Enemies spawn at random positions within level bounds
• MoveInitializer - Random initial movement direction for spawned entities
• SpinComponent - Visual rotation effect on enemies
• Level Bounds - Enemies reflect off arena boundaries
• GameObjectFactory - Fluent builder pattern for creating GameObjects
• State Management - Game state tracking via Session
• Automated Rendering - SceneRenderingSystem handles viewport-based rendering

Building

cmake -S . -B build
cmake --build build --target enemy_spawnmain

Running

./build/examples/enemy_spawn/main

Controls

Input	Action
Left Stick	Move spaceship / Rotate
ESC	Exit application
~ (Tilde)	Toggle ImGui overlay

Code Structure

File	Purpose
main.cpp	Application entry point with spawn configuration

Components Used

Component	Purpose
SceneNodeComponent	Links GameObject to scene graph
Move2DComponent	2D physics with velocity and acceleration
SpinComponent	Continuous rotation animation
ComposeTransformComponent	Local/world transform composition
ScaleStateComponent	Unit-based sizing (meters)
LevelBoundsBehaviorComponent	Reflect behavior at arena boundaries
AabbColliderComponent	World-space collision bounds
SpawnedByProfileComponent	Links entity to spawn profile
PrefabIdComponent	Identifies prefab type for pooling
Active / Inactive	Entity activation state tags

Systems Used

System	Purpose
GameObjectSpawnSystem	Processes spawn schedulers and triggers spawning
SpinSystem	Applies rotation from SpinComponent
Move2DSystem	Physics simulation (velocity integration)
SteeringSystem	Direction-based rotation
ScaleSystem	Applies ScaleStateComponent sizing
BoundsUpdateSystem	Updates AABB colliders from transforms
LevelBoundsBehaviorSystem	Handles boundary reflections
ComposeTransformSystem	Computes final transforms
StateToViewportPolicyUpdateSystem	Activates viewports based on game state
SceneSyncSystem	Syncs transforms to scene graph
SceneRenderingSystem	Renders scenes to associated viewports
TransformClearSystem	Clears dirty flags post-frame

Spawn System Configuration (DSL)

SpawnSystemFactory::configure(poolManager, spawnManager)
    .pool(EnemyPoolId, EnemyPrefabId, 200)
        .profile(RandomSpawnProfileId)
            .randomPlacement()
            .randomDirectionInitializer()
            .scheduledBy(SpawnRuleId)
                .timerCondition(5.0f)
                .fixedAmount(1)
                .done()
            .done()
        .commit();

GameLoop Phase Configuration

// Pre-Phase: Input, Spawning, Physics
gameLoop.phase(PhaseType::Pre)
    .addPass<GameState>(GameState::Any)
    .addSystem<TwinStickInputSystem>(shipGameObject)
    .addCommitPoint(CommitPoint::Structural)
    .addPass<GameState>(GameState::Any)
    .addSystem<GameObjectSpawnSystem>(spawnManager)
    .addCommitPoint(CommitPoint::Structural)
    .addPass<GameState>(GameState::Any)
    .addSystem<ScaleSystem>()
    .addSystem<SteeringSystem>()
    .addSystem<SpinSystem>()
    .addSystem<Move2DSystem>();

// Main-Phase: Collision Detection
gameLoop.phase(PhaseType::Main)
    .addPass<GameState>(GameState::Any)
    .addSystem<BoundsUpdateSystem>()
    .addSystem<LevelBoundsBehaviorSystem>()
    .addCommitPoint();

// Post-Phase: Transform and Rendering
gameLoop.phase(PhaseType::Post)
    .addPass<GameState>(GameState::Any)
    .addSystem<ComposeTransformSystem>()
    .addSystem<StateToViewportPolicyUpdateSystem<GameState, MatchState>>(stateToViewportMap)
    .addSystem<SceneSyncSystem>(sceneToViewportMap)
    .addSystem<SceneRenderingSystem>(renderingDevice, sceneToViewportMap)
    .addSystem<TransformClearSystem>();

See Also

• Spawn System - Spawn pipeline and DSL builder
• Object Pooling - Entity pooling system
• Game Loop Architecture - Phase-based game loop
• Collision Detection Example - Grid-based collision
• Scoring Demo - Full gameplay with scoring and menus