The Game Loop

Every game runs a continuous loop: read input, update state, render graphics. PIGO8 handles the loop for you through three methods.

Init, Update, Draw

type Cartridge interface {
    Init()   // Called once when the game starts
    Update() // Called every frame (default: 30 times/second)
    Draw()   // Called every frame after Update
}

Init

Runs once before the first frame. Use it to:

Set initial positions
Load level data
Initialize scores

func (g *game) Init() {
    g.playerX = 64
    g.playerY = 64
    g.score = 0
}

Update

Runs every frame before Draw. Use it to:

Read input
Move game objects
Check collisions
Update game state

func (g *game) Update() {
    if p8.Btn(p8.LEFT) {
        g.playerX--
    }
    if p8.Btn(p8.RIGHT) {
        g.playerX++
    }
}

Important: Never draw in Update. Drawing operations only work in Draw.

Draw

Runs every frame after Update. Use it to:

Clear the screen
Draw backgrounds, sprites, and UI
Render everything visible

func (g *game) Draw() {
    p8.Cls(0)                          // Always clear first
    p8.Spr(1, g.playerX, g.playerY)    // Draw player sprite
    p8.Print(g.score, 2, 2, 7)         // Draw score
}

Frame Timing

By default, PIGO8 runs at 30 FPS (frames per second). Each frame:

Update() is called
Draw() is called
The screen is displayed
Wait until the next frame is due

At 30 FPS, each frame is ~33 milliseconds. At 60 FPS, each frame is ~16 milliseconds.

Changing FPS

Use settings to change the frame rate:

func main() {
    settings := p8.NewSettings()
    settings.TargetFPS = 60  // Smoother animation
    
    p8.InsertGame(&game{})
    p8.PlayGameWith(settings)
}

Higher FPS means smoother animation but faster game speed if you're using fixed movement values. Consider using delta time for frame-rate independent movement.

Time Function

Get the elapsed time since the game started:

func (g *game) Update() {
    elapsed := p8.Time()  // Returns seconds as float64
    
    // Do something every 2 seconds
    if int(elapsed) % 2 == 0 {
        // ...
    }
}

Complete Example: Moving Square

package main

import p8 "github.com/drpaneas/pigo8"

type game struct {
    x, y float64
}

func (g *game) Init() {
    g.x = 60
    g.y = 60
}

func (g *game) Update() {
    if p8.Btn(p8.LEFT)  { g.x-- }
    if p8.Btn(p8.RIGHT) { g.x++ }
    if p8.Btn(p8.UP)    { g.y-- }
    if p8.Btn(p8.DOWN)  { g.y++ }
}

func (g *game) Draw() {
    p8.Cls(0)
    p8.Rectfill(g.x, g.y, g.x+8, g.y+8, 8)  // Red square
}

func main() {
    p8.InsertGame(&game{})
    p8.Play()
}

Arrow keys move the red square. The game loop makes it responsive.

PIGO8 Documentation