Game engine architecture overview in Unity - Step-by-Step Execution

Concept Flow - Game engine architecture overview

Start Game Engine

↓

Initialize Core Systems

↓

Load Assets & Resources

↓

Game Loop Start

↓

Process Input

→Update Game Logic

↓

Check Exit Condition

↓

Repeat Game Loop

↓

Shutdown & Cleanup

This flow shows how a game engine starts, runs its main loop processing input, updating logic, rendering frames, and then shuts down.

Execution Sample

Unity

void Update() {
    ProcessInput();
    UpdateGameLogic();
    RenderFrame();
}

This code runs every frame to handle input, update game state, and draw the scene.

Execution Table

Frame	ProcessInput	UpdateGameLogic	RenderFrame	Exit Condition	Action
1	Read keyboard/mouse	Move player, check collisions	Draw scene to screen	False	Continue loop
2	Read keyboard/mouse	Update NPCs, physics	Draw updated scene	False	Continue loop
3	Read keyboard/mouse	Check win/lose state	Draw final frame	True	Exit loop

💡 Exit condition true at frame 3, game loop ends

Variable Tracker

Variable	Start	After Frame 1	After Frame 2	After Frame 3
PlayerPosition	(0,0)	(1,0)	(2,0)	(2,0)
GameRunning	True	True	True	False
FrameCount	0	1	2	3

Key Moments - 2 Insights

Why does the game loop keep running even though we process input and update logic every frame?

Because the exit condition is checked after processing input, updating logic, and rendering. The loop continues until the exit condition becomes true, as shown in the execution_table rows 1 and 2.

What happens if the exit condition becomes true during the game loop?

The loop stops after completing the current frame's processing, as seen in frame 3 of the execution_table where the exit condition is true and the action is to exit the loop.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of GameRunning after frame 2?

A Undefined

B True

C False

D Null

💡 Hint

Check variable_tracker row for GameRunning after Frame 2

At which frame does the exit condition become true according to the execution_table?

A Frame 1

B Frame 2

C Frame 3

D Never

💡 Hint

Look at the Exit Condition column in execution_table

If the RenderFrame step was skipped, what would likely happen in the game loop?

A The game would not display changes on screen

B The game would not update logic

C The input would not be processed

D The exit condition would never be checked

💡 Hint

RenderFrame draws the scene; skipping it means no visual update

Concept Snapshot

Game engine runs a loop every frame:
- Process input from player
- Update game logic (movement, physics, AI)
- Render the frame to display
Loop continues until exit condition is true
Core systems initialize before loop and cleanup after

Full Transcript

A game engine starts by initializing core systems and loading assets. Then it enters the main game loop. Each frame, it processes player input, updates the game logic like moving characters and checking collisions, and renders the frame to the screen. After rendering, it checks if the game should exit. If not, it repeats the loop. When the exit condition is true, the loop ends and the engine shuts down. Variables like player position and frame count update each frame. This cycle keeps the game running smoothly and responding to player actions.