Starwards Pixijs

PixiJS v8 Development for Starwards

Overview

Starwards uses PixiJS v8 (^8.14.0) for 2D rendering in the browser module. This skill covers both the PixiJS v8 API reference and Starwards-specific patterns.

Core principle: Layered container composition with ticker-driven updates synced to Colyseus state changes.

Table of Contents

1. PixiJS v8 Reference
   • Application
   • Containers & Scene Graph
   • Sprites
   • Graphics (v8 API)
   • Text
   • Textures & Assets
   • Ticker
   • Events / Interaction
   • Performance Tips
   • v8 Migration Guide
2. Starwards Patterns
   • CameraView Application
   • Layer System
   • Graphics Patterns
   • Event Handling
   • Object Pooling
   • Testing with Playwright

PixiJS v8 Reference

Application

The Application class provides an extensible entry point for PixiJS projects.

Async Initialization (v8 Required)

import { Application } from 'pixi.js';

const app = new Application();

await app.init({
  width: 800,
  height: 600,
  backgroundColor: 0x1099bb,
});

document.body.appendChild(app.canvas);

Key Options

Containers & Scene Graph

Creating Containers

import { Container } from 'pixi.js';

const container = new Container({
  x: 100,
  y: 100,
});

app.stage.addChild(container);

Parent-Child Relationships

• Children inherit transforms, alpha, visibility from parents
• Render order: children render in insertion order (later = on top)
• Use setChildIndex() or zIndex with sortableChildren for reordering

Coordinate Systems

// Local to global
const globalPos = obj.toGlobal(new Point(0, 0));

// Global to local
const localPos = container.toLocal(new Point(100, 100));

Culling

container.cullable = true;        // Enable culling
container.cullableChildren = true; // Cull children recursively
container.cullArea = new Rectangle(0, 0, 400, 400); // Custom cull bounds

Sprites

Basic Usage

import { Sprite, Assets } from 'pixi.js';

const texture = await Assets.load('bunny.png');
const sprite = new Sprite(texture);

sprite.anchor.set(0.5);  // Center anchor
sprite.x = 100;
sprite.y = 100;
sprite.tint = 0xff0000;  // Red tint
sprite.alpha = 0.8;

Sprite Properties

Graphics (v8 API)

CRITICAL: v8 uses a new fluent API. Build shapes first, then fill/stroke.

v8 Fluent API

import { Graphics } from 'pixi.js';

// Draw shape, then fill/stroke
const graphics = new Graphics()
  .rect(50, 50, 100, 100)
  .fill(0xff0000)
  .stroke({ width: 2, color: 'white' });

// Circle with fill and stroke
const circle = new Graphics()
  .circle(100, 100, 50)
  .fill({ color: 0x00ff00, alpha: 0.5 })
  .stroke({ width: 3, color: 0x000000 });

Shape Methods

Lines

const lines = new Graphics()
  .moveTo(0, 0)
  .lineTo(100, 100)
  .lineTo(200, 0)
  .stroke({ width: 2, color: 0xff0000 });

Holes (v8)

const rectWithHole = new Graphics()
  .rect(0, 0, 100, 100)
  .fill(0x00ff00)
  .circle(50, 50, 20)
  .cut();  // Creates hole

GraphicsContext (Sharing)

import { GraphicsContext, Graphics } from 'pixi.js';

const context = new GraphicsContext()
  .rect(0, 0, 100, 100)
  .fill(0xff0000);

const g1 = new Graphics(context);
const g2 = new Graphics(context); // Shares same data

Text

Basic Text

import { Text, TextStyle } from 'pixi.js';

const text = new Text({
  text: 'Hello World',
  style: {
    fontFamily: 'Arial',
    fontSize: 24,
    fill: 0xffffff,
    align: 'center',
  },
});

TextStyle Properties

BitmapText (Performance)

import { BitmapText } from 'pixi.js';

const bitmapText = new BitmapText({
  text: 'Score: 1000',
  style: { fontFamily: 'MyBitmapFont', fontSize: 32 },
});

Textures & Assets

Loading Assets

import { Assets, Sprite } from 'pixi.js';

// Single asset
const texture = await Assets.load('path/to/image.png');
const sprite = new Sprite(texture);

// Multiple assets
const textures = await Assets.load(['a.png', 'b.png']);

// With alias
await Assets.load({ alias: 'hero', src: 'images/hero.png' });
const heroTexture = Assets.get('hero');

Asset Bundles

Assets.addBundle('game', [
  { alias: 'player', src: 'player.png' },
  { alias: 'enemy', src: 'enemy.png' },
]);

const assets = await Assets.loadBundle('game');

Manifest

const manifest = {
  bundles: [
    {
      name: 'load-screen',
      assets: [{ alias: 'bg', src: 'background.png' }],
    },
    {
      name: 'game',
      assets: [{ alias: 'hero', src: 'hero.png' }],
    },
  ],
};

await Assets.init({ manifest });
await Assets.loadBundle('load-screen');

SVGs

// As texture
const svgTexture = await Assets.load('icon.svg');
const sprite = new Sprite(svgTexture);

// As Graphics (scalable)
const svgContext = await Assets.load({
  src: 'icon.svg',
  data: { parseAsGraphicsContext: true },
});
const graphics = new Graphics(svgContext);

Texture Cleanup

// Unload from cache and GPU
await Assets.unload('texture.png');

// Unload from GPU only (keep in memory)
texture.source.unload();

// Destroy texture
texture.destroy();

Ticker

Basic Usage

import { Ticker, UPDATE_PRIORITY } from 'pixi.js';

// Using app ticker
app.ticker.add((ticker) => {
  sprite.rotation += 0.1 * ticker.deltaTime;
});

// One-time callback
app.ticker.addOnce((ticker) => {
  console.log('Called once');
});

// With priority (higher runs first)
app.ticker.add(updateFn, null, UPDATE_PRIORITY.HIGH);

Priority Constants

• UPDATE_PRIORITY.HIGH = 50
• UPDATE_PRIORITY.NORMAL = 0
• UPDATE_PRIORITY.LOW = -50

FPS Control

app.ticker.maxFPS = 60;  // Cap framerate
app.ticker.minFPS = 30;  // Clamp deltaTime

Ticker Properties

Events / Interaction

Event Modes

sprite.eventMode = 'static';  // Interactive, non-moving
sprite.eventMode = 'dynamic'; // Interactive, moving (receives idle events)
sprite.eventMode = 'passive'; // Default, children can be interactive
sprite.eventMode = 'none';    // No interaction

Pointer Events

sprite.eventMode = 'static';

sprite.on('pointerdown', (event) => {
  console.log('Clicked at', event.global.x, event.global.y);
});

sprite.on('pointermove', (event) => { /* ... */ });
sprite.on('pointerup', (event) => { /* ... */ });
sprite.on('pointerover', (event) => { /* ... */ });
sprite.on('pointerout', (event) => { /* ... */ });

Hit Area

import { Rectangle, Circle } from 'pixi.js';

sprite.hitArea = new Rectangle(0, 0, 100, 100);
// or
sprite.hitArea = new Circle(50, 50, 50);

Custom Cursor

sprite.cursor = 'pointer';
sprite.cursor = 'grab';
sprite.cursor = 'url(cursor.png), auto';

Disable Children Interaction

container.interactiveChildren = false; // Skip children hit testing

Performance Tips

Sprites

• Use spritesheets to minimize texture switches
• Sprites batch with up to 16 textures per batch
• Draw order matters for batching efficiency

Graphics

• Graphics are fastest when not modified after creation
• Small Graphics (<100 points) batch like sprites
• Use sprites with textures for complex shapes

Text

• Avoid updating text every frame (expensive)
• Use BitmapText for frequently changing text
• Lower resolution for less memory

Masks

• Rectangle masks (scissor) are fastest
• Graphics masks (stencil) are second fastest
• Sprite masks (filters) are expensive

Filters

• Release with container.filters = null
• Set filterArea for known dimensions
• Use sparingly - each filter adds draw calls

General

• Enable culling for large scenes: cullable = true
• Use RenderGroups for static content
• Set interactiveChildren = false for non-interactive containers

v8 Migration Highlights

Key Changes

1. Async Initialization Required

// OLD (v7)
const app = new Application({ width: 800 });

// NEW (v8)
const app = new Application();
await app.init({ width: 800 });

2. Graphics API Changed

// OLD (v7)
graphics.beginFill(0xff0000).drawRect(0, 0, 100, 100).endFill();

// NEW (v8)
graphics.rect(0, 0, 100, 100).fill(0xff0000);

3. Ticker Callback

// OLD (v7)
ticker.add((dt) => sprite.rotation += dt);

// NEW (v8)
ticker.add((ticker) => sprite.rotation += ticker.deltaTime);

4. Application Canvas

// OLD (v7)
app.view

// NEW (v8)
app.canvas

5. Leaf Nodes Can't Have Children

• Sprite, Graphics, Mesh etc. can no longer have children
• Use Container as parent instead

6. getBounds Returns Bounds

// OLD (v7)
const rect = container.getBounds();

// NEW (v8)
const rect = container.getBounds().rectangle;

Starwards Patterns

CameraView Application

Starwards extends Application for radar/tactical views.

Location: modules/browser/src/radar/camera-view.ts

import { Application, ApplicationOptions, Container } from 'pixi.js';

export class CameraView extends Application {
  constructor(public camera: Camera) {
    super();
  }

  public async initialize(
    pixiOptions: Partial<ApplicationOptions>,
    container: WidgetContainer
  ) {
    await super.init(pixiOptions);

    // Limit FPS to prevent GPU heating
    this.ticker.maxFPS = 30;

    // Handle resize
    container.on('resize', () => {
      this.resizeView(container.width, container.height);
    });

    // Append canvas
    container.getElement().append(this.canvas);
  }

  // Coordinate transformations
  public worldToScreen = (w: XY) => this.camera.worldToScreen(this.renderer, w.x, w.y);
  public screenToWorld = (s: XY) => this.camera.screenToWorld(this.renderer, s.x, s.y);

  // Layer management
  public addLayer(child: Container) {
    this.stage.addChild(child);
  }
}

Key patterns:

• ticker.maxFPS = 30 - Prevents excessive GPU usage
• Coordinate transforms: worldToScreen(), screenToWorld()
• Layer composition via addLayer()

Layer System

Starwards uses a layer pattern where each layer has a renderRoot Container.

GridLayer Example

Location: modules/browser/src/radar/grid-layer.ts

import { Container, Graphics } from 'pixi.js';

export class GridLayer {
  private stage = new Container();
  private gridLines = new Graphics();

  constructor(private parent: CameraView) {
    this.parent.events.on('screenChanged', () => this.drawSectorGrid());
    this.stage.addChild(this.gridLines);
  }

  get renderRoot(): Container {
    return this.stage;
  }

  private drawSectorGrid() {
    // Clear and redraw
    this.gridLines.clear();

    // Draw lines using v8 API
    this.gridLines
      .moveTo(0, screen)
      .lineTo(this.parent.renderer.width, screen)
      .stroke({ width: 2, color: magnitude.color, alpha: 0.5 });
  }
}

Pattern:

• Each layer owns a stage Container
• Exposes via renderRoot getter
• Redraws on screenChanged event
• Uses graphics.clear() before redrawing

Starwards Graphics Patterns

v8 Fluent API Usage

// Drawing selection rectangle
const graphics = new Graphics();
graphics
  .rect(min.x, min.y, width, height)
  .fill({ color: selectionColor, alpha: 0.2 })
  .stroke({ width: 1, color: selectionColor, alpha: 1 });

// Drawing grid lines
this.gridLines
  .moveTo(0, screenY)
  .lineTo(rendererWidth, screenY)
  .stroke({ width: 2, color: lineColor, alpha: 0.5 });

Clear and Redraw Pattern

private redraw() {
  this.graphics.clear();
  // ... draw new content
}

Starwards Event Handling

Location: modules/browser/src/radar/interactive-layer.ts

Setup

import { Container, FederatedPointerEvent, Rectangle } from 'pixi.js';

export class InteractiveLayer {
  private stage = new Container();

  constructor(private parent: CameraView) {
    // Set cursor
    this.stage.cursor = 'crosshair';

    // Enable interaction
    this.stage.interactive = true;

    // Set hit area to full canvas
    this.stage.hitArea = new Rectangle(
      0, 0,
      this.parent.renderer.width,
      this.parent.renderer.height
    );

    // Register events
    this.stage.on('pointerdown', this.onPointerDown);
    this.stage.on('pointermove', this.onPointerMove);
    this.stage.on('pointerup', this.onPointerUp);

    // Update hit area on resize
    this.parent.events.on('screenChanged', () => {
      this.stage.hitArea = new Rectangle(
        0, 0,
        this.parent.renderer.width,
        this.parent.renderer.height
      );
    });
  }

  private FederatedPointerEvent) => {
    const screenPos = XY.clone(event.global);
    const worldPos = this.parent.screenToWorld(screenPos);
    // ... handle interaction
  };
}

Key patterns:

• stage.interactive = true enables events
• stage.hitArea = new Rectangle(...) defines clickable area
• Update hit area on resize
• Use event.global for screen coordinates
• Convert to world with screenToWorld()

Object Pooling

Location: modules/browser/src/radar/texts-pool.ts

Starwards uses iterator-based pooling to reduce GC pressure.

export class TextsPool {
  private texts: Text[] = [];

  constructor(private container: Container) {}

  *[Symbol.iterator]() {
    let index = 0;
    while (true) {
      if (index >= this.texts.length) {
        const text = new Text({ text: '', style: { ... } });
        this.texts.push(text);
        this.container.addChild(text);
      }
      const text = this.texts[index];
      text.visible = true;
      yield text;
      index++;
    }
  }

  return() {
    // Hide unused texts
    for (let i = this.usedCount; i < this.texts.length; i++) {
      this.texts[i].visible = false;
    }
  }
}

// Usage
const textsIterator = this.textsPool[Symbol.iterator]();
for (const item of items) {
  const text = textsIterator.next().value;
  text.text = item.label;
  text.x = item.x;
  text.y = item.y;
}
textsIterator.return(); // Hide unused

Testing with Playwright

Data Attributes

Add data-id to canvas elements for E2E testing:

this.canvas.setAttribute('data-id', 'Tactical Radar');

Playwright Selectors

// Select canvas by data-id
const canvas = page.locator('[data-id="Tactical Radar"]');

// Get attribute values
const zoom = await canvas.getAttribute('data-zoom');

Testing Considerations

• No unit tests for PixiJS components (visual output)
• Use E2E tests with Playwright
• Test via data attributes, not rendered pixels
• Use data-id on Tweakpane panels: page.locator('[data-id="Panel Name"]')

Quick Reference

Common Pitfalls

1. Using v7 Graphics API

   • Wrong: beginFill(), drawRect(), endFill()
   • Right: rect().fill().stroke()

2. Forgetting async init

   • Wrong: new Application({ width: 800 })
   • Right: await app.init({ width: 800 })

3. Adding children to Sprites

   • v8 leaf nodes can't have children
   • Use Container as parent

4. Not clearing Graphics

   • Call graphics.clear() before redrawing

5. Hit area not updated on resize

   • Update stage.hitArea when canvas resizes

6. SVGs not loading as textures

   • Use Texture.from() for SVGs (GitHub issue #8694 workaround)