Tutorial 4: Building a First Playable Prototype

Unit 1 Β· Game loops and real-time systems

Objectives

Prototype around a verb

A useful first prototype is small enough to finish in one sitting. Choose one verb such as move, dodge, collect, or aim. Add only the systems needed to make that verb understandable: input, state, collision or target rules, rendering, and feedback.

while (running) {
    double delta = clock.secondsSinceLastFrame();
    Input input = inputSystem.poll();
    game.update(input, Math.min(delta, 0.25));
    renderer.draw(game.snapshot());
}

Write an acceptance test before polishing: β€œA new player can move to the target, collect it, see feedback, and restart after failure.” This keeps the prototype playable and makes missing behavior visible.

Exercises

  1. Write a one-sentence core loop using three or four verbs.
  2. Create a minimum feature list and a cut list.
  3. Trace one successful play session and one failure/restart session.

Self-check

  1. What makes a prototype playable?
  2. Why define an acceptance test early?
  3. Which system should own restart behavior?

Self-Check Quiz

1. What should a first prototype optimize for?

AnswerIt should optimize for a clear, testable core interaction rather than a large feature count.

2. What is a cut list?

AnswerA list of optional features that can be removed to protect the playable milestone.

3. Why cap the delta in the loop?

AnswerTo prevent a pause or hitch from causing an extreme movement or simulation jump.

Homework

  1. Build a one-screen prototype with one player action, one goal, one failure condition, and restart.
  2. Document the loop phases and state transitions.
  3. Ask one person to play for two minutes and record where they hesitate.
Sample answer

A complete prototype might let the player move a square to a target while avoiding one hazard. The game has TITLE, PLAYING, and GAME_OVER states; update handles movement and collisions, render draws the current state, and restart resets position and score. The playtest record should describe observed behavior, not just opinions.

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