praca_magisterska/games/unreal/tutorial/part-5-create-spawner.md

Part 5: Create Enemy Spawner

← Previous: Part 4 - Create the Enemy | Back to Index | Next: Part 6 - Game Director →

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Step 5.1: Create Spawner Blueprint

1. Content Browser → Blueprints

2. Right-click → Blueprint Class → Actor

3. Name: BP_EnemySpawner

4. Double-click to open

5. Create Variables:

Variable Name	Type	Default Value
EnemyClass	Class Reference	(will reference BP_Enemy)
SpawnAreaHalfWidth	Float	900.0
GameDuration	Float	300.0 (5 minutes)
MaxSimultaneousEnemies	Integer	120
ElapsedTime	Float	0.0
SpawnTimer	Float	0.0
SpawningActive	Boolean	true

Expected Result after Compile

• Compile button shows GREEN checkmark
• Variables panel shows all 7 variables with correct types
• No components needed (spawner is invisible logic actor)

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Step 5.2: Spawn Rate Curve

1. Create Variable

• SpawnCurve (Curve Float)

2. To create the curve asset

1. In Content Browser, right-click → Miscellaneous → Curve
2. Select "CurveFloat"
3. Name it SpawnRateCurve
4. Double-click to open Curve Editor

3. In Curve Editor

• Right-click on the curve → Add Key
• Create these keyframes:

Time	Value	Description
0.0	0.4	slow spawn at start
0.5	2.0	medium spawn halfway
1.0	4.5	fast spawn at end

• The X axis is normalized time (0-1)
• The Y axis is spawns per second

4. In BP_EnemySpawner, set SpawnCurve default to this curve asset

Expected Result in Curve Editor

• Curve line visible starting at (0, 0.4), rising through (0.5, 2.0), ending at (1.0, 4.5)
• Smooth interpolation between keyframes

Expected Result in Play mode

• Game start: ~0.4 enemies spawn per second (slow)
• At 2.5 minutes: ~2 enemies spawn per second (medium)
• At 5 minutes: ~4.5 enemies spawn per second (intense)

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Step 5.3: Spawning Logic

1. In Event Graph, from Event Tick

a) Check if SpawningActive is true

• If false, do nothing

b) Update ElapsedTime

• Add DeltaSeconds to ElapsedTime

c) Calculate normalized time

• Divide ElapsedTime by GameDuration
• Clamp between 0 and 1

d) Get spawn rate from curve

• Get SpawnCurve
• Call Get Float Value with normalized time
• This returns spawns per second

e) Update SpawnTimer

• Subtract DeltaSeconds from SpawnTimer
• If SpawnTimer <= 0:
  • Reset SpawnTimer to (1.0 / SpawnsPerSecond)
  • Call SpawnWave function

2. CREATE "SpawnWave" FUNCTION

a) Inside

• Calculate burst size based on time:

  BaseCount = 1 + (NormalizedTime * 6)
  BurstSize = BaseCount + Random(0, 2)
  Clamp between 1 and 12
  

b) For Loop from 0 to BurstSize - 1

• Call SpawnEnemy function

3. CREATE "SpawnEnemy" FUNCTION

a) Inside

• Check: Get All Actors of Class (BP_Enemy)
  • Get array length
  • If >= MaxSimultaneousEnemies: Return (don't spawn)

b) Calculate spawn position

• X = Random Float in Range (-SpawnAreaHalfWidth, SpawnAreaHalfWidth)
• Y = Get this actor's Y position (top of screen)
• Z = 0

c) Spawn Actor from Class

• Class: EnemyClass
• Location: calculated position
• Rotation: (0, 0, 0)

4. CREATE "StopSpawning" FUNCTION

• Set SpawningActive = false

Expected Result after Compile

• Compile button shows GREEN checkmark
• "SpawnWave", "SpawnEnemy", "StopSpawning" functions appear under Functions

Expected Result in Play mode

• Enemies spawn at top of screen (Y=500) at random X positions
• Spawn rate increases over time following the curve
• Maximum 120 enemies on screen at once
• When StopSpawning called: No new enemies appear

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← Previous: Part 4 - Create the Enemy | Back to Index | Next: Part 6 - Game Director →