PLECK lesson 42 · suggested week 9, day 2
Constrain randomness for a fair challenge
Objective. Distinguish unpredictable variation from unavoidable failure.
Godot Engine Standard desktop editor 4.7.2-stable, GDScript (Godot 4), Compatibility renderer. Headless Godot 4.7.2.stable.official.ed1daf0bf passed 106 assertions on the supplied scaffolds, including malformed JSON saves. Audio used the Dummy driver and a synthetic WAV, not a speaker. The visual editor, browser export, and signed-in submission were not tested. The desk still does not run a student's own upload.
About 55 minutes. The due date is chosen by a parent.
Fair randomization, difficulty, accessibility and assessment
Suggested pace: Recall and predict 5 min; Read instruction and scaffold 12 min; Build or design the assigned artifact 25 min; Run acceptance tests 8 min; Explain and checkpoint 5 min.
Materials: Godot Standard 4.7.2 desktop editor (GDScript, Compatibility renderer), Local course folder and prior checkpoint, No paid assets or public account required.
Comes after VGC-L041.
Random x positions create variation but can accidentally block every escape route. Constrain hazards to a minimum horizontal separation or spawn one at a time with enough travel time to react. Estimate travel: at 110 pixels per second, a hazard from y-20 to y180 takes about 1.82 seconds. Compare that with player speed and route width. A random system needs invariants such as at least one navigable lane; “it usually works” is not enough for a fair rule.
Worked example
An incoming three-lane wave blocks left and center but leaves right clear. Randomly choosing among valid two-lane combinations creates variation while preserving an escape route. Scaffold C-TIMER — Timer-based spawning with a hard cap Setup: World Node2D root contains Node2D Hazards and Timer SpawnTimer: wait_time 1.2, autostart On, one_shot Off. Hazard scene root Area2D has a CircleShape2D radius 12 and C-HAZARD. Attach script to World and drag Hazard.tscn into hazard_scene Inspector field. Set viewport 640x360. Name Hazards group not needed. This script is a separate lab; merge its _ready into an existing manager rather than declaring a second _ready. ```gdscript extends Node2D @export var hazard_scene: PackedScene @export var spawn_limit: int = 12 func _ready() -> void: $SpawnTimer.timeout.connect(_spawn) func _spawn() -> void: if hazard_scene == null or $Hazards.get_child_count() >= spawn_limit: return var hazard := hazard_scene.instantiate() as Area2D $Hazards.add_child(hazard) hazard.position = Vector2(randf_range(20.0, 620.0), -20.0) ```
Timer-based spawning with a hard cap
GDScript (Godot 4, not Scratch, Python, JavaScript or C#). Scaffold C-TIMER. Copy starts from this text. The desk does not run it.
Scene and node setup
World Node2D root contains Node2D Hazards and Timer SpawnTimer: wait_time 1.2, autostart On, one_shot Off. Hazard scene root Area2D has a CircleShape2D radius 12 and C-HAZARD. Attach script to World and drag Hazard.tscn into hazard_scene Inspector field. Set viewport 640x360. Name Hazards group not needed. This script is a separate lab; merge its _ready into an existing manager rather than declaring a second _ready.
extends Node2D
@export var hazard_scene: PackedScene
@export var spawn_limit: int = 12
func _ready() -> void:
$SpawnTimer.timeout.connect(_spawn)
func _spawn() -> void:
if hazard_scene == null or $Hazards.get_child_count() >= spawn_limit:
return
var hazard := hazard_scene.instantiate() as Area2D
$Hazards.add_child(hazard)
hazard.position = Vector2(randf_range(20.0, 620.0), -20.0)
Checks to run in the editor
- One object appears about each 1.2 seconds.
- At most 12 hazards exist, even during a long run.
Native Godot 4.7.2.stable.official.ed1daf0bf headless compile and representative node-tree/runtime tests passed; see native-qa-results.json. Visual UI, audible output, exports and website submission still need separate checks.
Constrain randomness for a fair challenge — evidence task
- 1. Choose three 160-pixel-wide lanes and permit at most two occupied incoming lanes at one spawn wave.
- 2. Draw and test five possible wave layouts.
Deliverable. Lane rule, five layouts and revised spawner.
Acceptance checks
- VGC-L042-T1. Every wave leaves at least one clear lane.
- VGC-L042-T2. Your test includes both adjacent and separated blocked lanes.
Understanding question. Why is testing only one random run weak evidence?
Include a downloadable project ZIP with project.godot, .tscn, .gd and original asset files when code changes. A private, teacher-accessible download link to that ZIP is equivalent. Screenshots or a playthrough do not replace editable source.
If this is still shaky. Tune just hazard speed and spawn interval on a copied project. Use fixed test runs before adding more mechanics. Start with the first assigned task and re-run its acceptance test before adding the remaining feature.
Optional extra. Offer an optional challenge mode while retaining a gentle default. Document one changed parameter, your prediction, and the observed effect; optional, not required for completion.
Turn in typed notes and a JPEG, PNG, or WebP screenshot. One https address is stored as text and is not opened, extracted, or run. An MP3, WAV, M4A, MP4, or WebM file up to 4 MB can show a demo. The demo does not replace editable source. Zip and code files are refused. If there is no private link, keep the project on the family computer and review the code in person.
- Your first 2D game
Free public tutorial; no account; external asset download is optional, not used by this course.
· Opening this link does not submit the lesson.
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