scale-and-responsive

name	scale-and-responsive
description	Use this skill when making a Phaser 4 game responsive or handling display scaling. Covers ScaleManager, scale modes (FIT, RESIZE, EXPAND, ENVELOP), auto-center, fullscreen, and browser resize handling. Triggers on: ScaleManager, responsive, resize, fullscreen, FIT, scale mode.

Scale and Responsive Design

How to use the ScaleManager for scaling, centering, fullscreen, orientation handling, and responsive resize in Phaser 4.

Key source paths: src/scale/ScaleManager.js, src/scale/const/, src/scale/events/, src/core/typedefs/ScaleConfig.js Related skills: ../game-setup-and-config/SKILL.md

Quick Start

Scale-to-fit with centering -- the most common setup for responsive games:

const config = {
    type: Phaser.AUTO,
    scale: {
        parent: 'game-container',
        mode: Phaser.Scale.FIT,
        autoCenter: Phaser.Scale.CENTER_BOTH,
        width: 800,
        height: 600
    },
    scene: MyScene
};

const game = new Phaser.Game(config);

The scale config object is parsed into a Phaser.Core.Config instance which the ScaleManager reads during boot. The ScaleManager sets the canvas element size and applies CSS scaling to fit it within its parent.

Core Concepts

ScaleManager (src/scale/ScaleManager.js)

The ScaleManager is created during the Game boot sequence and is accessible at game.scale or this.scale from within a Scene. It extends EventEmitter.

Three internal Size components drive all calculations:

Component	Property	Purpose
gameSize	game.scale.gameSize	The unmodified game dimensions from config. Used for world bounds, cameras. Read via game.scale.width / game.scale.height.
baseSize	game.scale.baseSize	The auto-rounded gameSize. Sets the actual canvas.width and canvas.height attributes.
displaySize	game.scale.displaySize	The CSS-scaled canvas size after applying scale mode, parent bounds, and zoom. Sets canvas.style.width / canvas.style.height.

Scaling works by keeping the canvas element dimensions fixed (baseSize) and stretching it via CSS properties (displaySize). This is equivalent to CSS transform-scale but without browser prefix issues.

The displayScale property (Phaser.Math.Vector2) holds the ratio baseSize / canvasBounds and is used internally for input coordinate transformation.

Scale Modes (src/scale/const/SCALE_MODE_CONST.js)

All modes are on Phaser.Scale.ScaleModes and are set via scale.mode in config:

Constant	Value	Behavior
NONE	0	No automatic scaling. Canvas uses config width/height. You manage sizing yourself. If you resize the canvas externally, call game.scale.resize(w, h) to update internals.
WIDTH_CONTROLS_HEIGHT	1	Height adjusts automatically to maintain aspect ratio based on width.
HEIGHT_CONTROLS_WIDTH	2	Width adjusts automatically to maintain aspect ratio based on height.
FIT	3	Scales to fit inside parent while preserving aspect ratio. May leave empty space (letterbox/pillarbox). Most commonly used mode.
ENVELOP	4	Scales to cover the entire parent while preserving aspect ratio. May extend beyond parent bounds (content gets cropped).
RESIZE	5	Canvas element itself is resized to fill parent. No CSS scaling -- 1:1 pixel mapping. The gameSize, baseSize, and displaySize all change to match parent. Beware of GPU fill-rate on large displays.
EXPAND	6	Hybrid of RESIZE and FIT. The visible area resizes to fill the parent, and the canvas scales to fit inside that area. Added in v3.80.

Shorthand constants are also available directly on Phaser.Scale: Phaser.Scale.FIT, Phaser.Scale.RESIZE, etc.

Center Modes (src/scale/const/CENTER_CONST.js)

Set via scale.autoCenter in config. Centering is achieved by setting CSS marginLeft and marginTop on the canvas:

Constant	Value	Behavior
NO_CENTER	0	No auto-centering (default).
CENTER_BOTH	1	Center horizontally and vertically within parent.
CENTER_HORIZONTALLY	2	Center horizontally only.
CENTER_VERTICALLY	3	Center vertically only.

The parent element must have calculable bounds. If the parent has no defined width/height, centering will not work correctly.

Zoom (src/scale/const/ZOOM_CONST.js)

Set via scale.zoom in config. Multiplies the display size:

Constant	Value	Behavior
NO_ZOOM	1	No zoom (default).
ZOOM_2X	2	2x zoom -- good for pixel art at low base resolution.
ZOOM_4X	4	4x zoom.
MAX_ZOOM	-1	Automatically calculates the largest integer zoom that fits in the parent.

You can also pass any numeric value. The zoom affects CSS display size but not the canvas resolution.

Orientation (src/scale/const/ORIENTATION_CONST.js)

Read via game.scale.orientation. Values are strings:

• Phaser.Scale.Orientation.LANDSCAPE = 'landscape-primary'
• Phaser.Scale.Orientation.LANDSCAPE_SECONDARY = 'landscape-secondary'
• Phaser.Scale.Orientation.PORTRAIT = 'portrait-primary'
• Phaser.Scale.Orientation.PORTRAIT_SECONDARY = 'portrait-secondary'

Convenience booleans: game.scale.isPortrait, game.scale.isLandscape (device orientation), game.scale.isGamePortrait, game.scale.isGameLandscape (game dimensions).

Common Patterns

FIT Mode with Centering (Most Common)

scale: {
    parent: 'game-container',
    mode: Phaser.Scale.FIT,
    autoCenter: Phaser.Scale.CENTER_BOTH,
    width: 1280,
    height: 720
}

The game maintains its 16:9 aspect ratio and centers within the parent. Empty space appears as letterbox/pillarbox bars. Style the parent's background color to control bar appearance.

Responsive Resize (Dynamic Canvas Size)

scale: {
    parent: 'game-container',
    mode: Phaser.Scale.RESIZE,
    width: '100%',
    height: '100%'
}

// In your scene -- respond to size changes:
create() {
    this.scale.on('resize', this.handleResize, this);
}

handleResize(gameSize, baseSize, displaySize) {
    this.cameras.resize(gameSize.width, gameSize.height);
    // Reposition UI elements based on new dimensions
}

Width/height accept percentage strings (e.g., '100%') which resolve against the parent size. If the parent has no size, they fall back to window.innerWidth / window.innerHeight.

Fullscreen Toggle

// Must be called from a pointerup gesture (not pointerdown)
this.input.on('pointerup', () => {
    if (this.scale.isFullscreen) {
        this.scale.stopFullscreen();
    } else {
        this.scale.startFullscreen();
    }
});

// Or use the convenience method:
this.input.on('pointerup', () => {
    this.scale.toggleFullscreen();
});

• startFullscreen(fullscreenOptions) -- requests browser fullscreen. Default options: { navigationUI: 'hide' }.
• stopFullscreen() -- exits fullscreen mode.
• toggleFullscreen(fullscreenOptions) -- toggles between the two.
• isFullscreen -- read-only boolean for current state.

If no fullscreenTarget is configured, Phaser creates a temporary <div>, moves the canvas into it, and sends that div fullscreen. The div is removed when leaving fullscreen.

For iframes, the allowfullscreen attribute is required.

Mobile Orientation Handling

create() {
    this.scale.on('orientationchange', (orientation) => {
        if (orientation === Phaser.Scale.LANDSCAPE) {
            // Show game UI
        } else {
            // Show "rotate device" message
        }
    });

    // Lock orientation (mobile browsers only, limited support):
    this.scale.lockOrientation('landscape');
}

Fixed Size (No Scaling)

scale: {
    mode: Phaser.Scale.NONE,
    width: 800,
    height: 600
}

In NONE mode, if you change the canvas size externally you must call game.scale.resize(newWidth, newHeight) to update all internal components including input coordinates.

Pixel Art with Max Zoom

scale: {
    mode: Phaser.Scale.FIT,
    autoCenter: Phaser.Scale.CENTER_BOTH,
    width: 320,
    height: 240,
    zoom: Phaser.Scale.MAX_ZOOM
},
pixelArt: true

MAX_ZOOM calculates the largest integer multiplier that fits in the parent. Combined with pixelArt: true (which disables anti-aliasing), this gives crisp pixel rendering.

Snap Values for Grid Alignment

scale: {
    mode: Phaser.Scale.FIT,
    width: 800,
    height: 600,
    snap: { width: 16, height: 16 }
}

When the browser resizes, dimensions snap down to the nearest grid multiple (using floor). Best used with FIT mode. Can also be set at runtime: game.scale.setSnap(16, 16) or reset with game.scale.setSnap().

Min/Max Size Constraints

scale: {
    mode: Phaser.Scale.FIT,
    width: 800,
    height: 600,
    min: { width: 400, height: 300 },
    max: { width: 1600, height: 1200 }
}

The display size is clamped to these bounds during scaling calculations.

Configuration Reference

ScaleConfig (src/core/typedefs/ScaleConfig.js)

All properties go inside the scale object in your game config:

Property	Type	Default	Description
width	number|string	1024	Base game width. Strings like '100%' resolve against parent size.
height	number|string	768	Base game height. Strings like '100%' resolve against parent size.
zoom	number|ZoomType	1	Canvas zoom factor. Use Phaser.Scale.MAX_ZOOM for auto.
parent	HTMLElement|string|null	undefined	Parent DOM element or its ID. undefined = document.body. null = no parent (you manage canvas placement).
expandParent	boolean	true	Allow ScaleManager to set parent/body CSS height to 100%.
mode	ScaleModeType	NONE	Scale mode constant (see table above).
min	{width, height}	-	Minimum canvas dimensions.
max	{width, height}	-	Maximum canvas dimensions.
snap	{width, height}	-	Snap values for resize rounding.
autoRound	boolean	false	Floor display/style sizes for low-powered device performance.
autoCenter	CenterType	NO_CENTER	Auto-centering mode (see table above).

Events (src/scale/events/)

All events are on Phaser.Scale.Events and are emitted by the ScaleManager instance (game.scale):

Event	String Value	Callback Signature	When
RESIZE	'resize'	(gameSize, baseSize, displaySize, previousWidth, previousHeight)	Any resize, refresh, or scale change. The three Size parameters have .width, .height, .aspectRatio.
ORIENTATION_CHANGE	'orientationchange'	(orientation)	Device orientation changes. orientation is a string constant from Phaser.Scale.Orientation.
ENTER_FULLSCREEN	'enterfullscreen'	()	Browser successfully enters fullscreen.
LEAVE_FULLSCREEN	'leavefullscreen'	()	Browser leaves fullscreen (via code or user ESC).
FULLSCREEN_FAILED	'fullscreenfailed'	(error)	Fullscreen request was denied by the browser.
FULLSCREEN_UNSUPPORTED	'fullscreenunsupported'	()	Browser does not support the Fullscreen API.

API Quick Reference

Key Properties (read-only unless noted)

Property	Type	Description
width	number	Game width (from gameSize.width).
height	number	Game height (from gameSize.height).
isFullscreen	boolean	Currently in fullscreen mode.
isPortrait	boolean	Device is in portrait orientation.
isLandscape	boolean	Device is in landscape orientation.
isGamePortrait	boolean	Game dimensions are taller than wide.
isGameLandscape	boolean	Game dimensions are wider than tall.
scaleMode	number	Current scale mode constant.
orientation	string	Current orientation string.
zoom	number	Current zoom factor.
autoRound	boolean	Whether sizes are auto-floored.
autoCenter	number	Current center mode constant.
parentSize	Size	Computed parent dimensions.
gameSize	Size	Unmodified game dimensions.
baseSize	Size	Canvas element dimensions.
displaySize	Size	CSS-scaled display dimensions.

Key Methods

Method	Returns	Description
resize(width, height)	this	For NONE mode: sets game, base, and display sizes directly. Updates canvas element and CSS.
setGameSize(width, height)	this	For scaled modes (FIT, etc.): changes the base game size and re-applies scaling.
setParentSize(width, height)	this	Manually set parent dimensions (useful when parent: null).
setZoom(value)	this	Change zoom factor at runtime.
setMaxZoom()	this	Set zoom to maximum integer that fits parent.
setSnap(snapWidth, snapHeight)	this	Set or reset snap grid values.
getMaxZoom()	number	Calculate (but don't apply) the max zoom.
getViewPort(camera?, out?)	Rectangle	Get the visible area rectangle, optionally for a specific camera.
refresh(prevW?, prevH?)	this	Force recalculation of scale, bounds, orientation. Emits RESIZE.
startFullscreen(options?)	void	Enter fullscreen. Must be called from pointerup.
stopFullscreen()	void	Exit fullscreen.
toggleFullscreen(options?)	void	Toggle fullscreen state.
lockOrientation(orientation)	boolean	Attempt to lock screen orientation (mobile only).
transformX(pageX)	number	Convert DOM pageX to game coordinate.

Gotchas

1. Parent element must have dimensions. The ScaleManager relies on the parent's computed CSS size. An unstyled <div> has zero height, which breaks centering and scaling. Either give it explicit CSS dimensions or let expandParent: true (the default) set body/parent to 100% height.

2. No padding on the parent. The ScaleManager does not account for parent padding. Apply padding to a wrapper element instead, or use margins on the parent's parent.

3. Do not style the canvas directly. The ScaleManager controls canvas.style.width, canvas.style.height, marginLeft, and marginTop. External CSS on the canvas will conflict.

4. Fullscreen requires pointerup, not pointerdown. On touch devices, pointerdown fullscreen requests are blocked unless the document already received touch input. Always use pointerup for reliable behavior.

5. Fullscreen in iframes needs allowfullscreen. Without this attribute on the iframe element, fullscreen requests will silently fail.

6. RESIZE mode and GPU fill-rate. RESIZE creates a 1:1 pixel canvas matching the parent. On high-resolution displays this can be very large. Monitor performance on low-end devices.

7. resize() vs setGameSize(). Use resize() only in NONE mode (it sets everything directly). Use setGameSize() when using FIT/ENVELOP/etc. (it preserves the scale mode calculations).

8. iOS height quirks. When the parent is the window on iOS, the ScaleManager uses GetInnerHeight to work around Safari's dynamic toolbar affecting getBoundingClientRect.

9. Percentage strings require a sized parent. Setting width: '100%' or height: '100%' resolves against parentSize. If the parent has no size, it falls back to window.innerWidth/innerHeight.

10. resizeInterval is a fallback poll. Modern browsers dispatch resize events, but the ScaleManager also polls every ms (default 500) to catch edge cases on older browsers.

Source File Map

File	Purpose
src/scale/ScaleManager.js	Main class -- all scaling, centering, fullscreen, orientation logic. Access via game.scale.
src/scale/const/SCALE_MODE_CONST.js	Scale mode constants: NONE, WIDTH_CONTROLS_HEIGHT, HEIGHT_CONTROLS_WIDTH, FIT, ENVELOP, RESIZE, EXPAND.
src/scale/const/CENTER_CONST.js	Center mode constants: NO_CENTER, CENTER_BOTH, CENTER_HORIZONTALLY, CENTER_VERTICALLY.
src/scale/const/ZOOM_CONST.js	Zoom constants: NO_ZOOM, ZOOM_2X, ZOOM_4X, MAX_ZOOM.
src/scale/const/ORIENTATION_CONST.js	Orientation string constants: LANDSCAPE, LANDSCAPE_SECONDARY, PORTRAIT, PORTRAIT_SECONDARY.
src/scale/events/RESIZE_EVENT.js	Resize event definition. Callback receives gameSize, baseSize, displaySize, previousWidth, previousHeight.
src/scale/events/ENTER_FULLSCREEN_EVENT.js	Emitted on successful fullscreen entry.
src/scale/events/LEAVE_FULLSCREEN_EVENT.js	Emitted when leaving fullscreen.
src/scale/events/FULLSCREEN_FAILED_EVENT.js	Emitted when fullscreen request is denied.
src/scale/events/FULLSCREEN_UNSUPPORTED_EVENT.js	Emitted when browser lacks Fullscreen API support.
src/scale/events/ORIENTATION_CHANGE_EVENT.js	Emitted on device orientation change. Callback receives orientation string.
src/core/typedefs/ScaleConfig.js	JSDoc typedef for the scale config object.
src/structs/Size.js	The Size component class used by gameSize, baseSize, displaySize.
src/dom/GetInnerHeight.js	iOS-specific workaround for getting accurate viewport height.
src/dom/GetScreenOrientation.js	Determines current screen orientation from dimensions.