--- title: "Shader backdrops" package: "@phaser-ae/backdrops" tier: Free version: 3.0.0-7 released: 2026-10-14 updated: 2026-10-20 description: "The runtime that draws full-screen shader backgrounds behind the world, stacked in the order you add them, aware of the camera and running on the game's clock." url: https://phaser.io/packs/backdrops site: Phaser - https://phaser.io --- # Shader backdrops A stack of full-screen shader backgrounds drawn before anything else in the frame: a sky, deep space, fog, or a texture that never runs out at the edge. Each layer knows the camera and the clock, changes live, and fades in and out on its own. ## What it does You add a backdrop by name, with params and colours that override its defaults, and it goes on top of the stack. The stack draws bottom-up with premultiplied alpha blending, before the sprites and tiles, so a translucent layer shows the one beneath it and an opaque one hides it. The usual stack is a sky gradient with stars or a nebula over it. A background picture can sit under the whole stack too, fitted by cover, contain or stretch, and a backdrop can sample it to warp or tint the art. Each frame every backdrop receives the camera's visible world rectangle and the interpolated simulation time. That is what lets a starfield slide with the camera at its own rate while a gradient ignores it, and why a backdrop pauses with the game and replays exactly. Every output also takes a still dither of half a colour level, so a smooth dark gradient does not show bands, and because the dither never changes over time a still sky stands perfectly still. The runtime owns the pass and the shader template but no looks. Each look is a small backdrop pack that registers a WGSL snippet, so a game carries only the backgrounds it uses, and a game can define its own for one scene. A backdrop that fails to compile is reported once with its name and skipped, rather than stopping the frame. ## Features - **A stack in add order** — backdrops blend bottom-up under every sprite and tile; `stack` lists them and `clear` empties it. - **Camera-aware** — a snippet reads the camera's visible world rectangle as `view` for parallax, or ignores it to stay pinned to the screen. - **On the simulation clock** — time pauses with the game and replays exactly; `handle.time` can be set to scrub or restart a backdrop. - **Live handles** — `set` and `setColor` change one value or several at once, all checked first so a bad name changes nothing. - **Tweens and fades** — `tween` eases params over simulation seconds along the `maths` eases; `show` and `hide` fade a layer in and out, and a hidden layer is not drawn at all. - **A background picture** — `background(key, fit)` draws any loaded image under the stack, and snippets can sample it as `bg` or `bgAt(uv)`. - **Your own backdrops** — `define` adds a backdrop the game owns, `registerBackdrop` is how a pack shares one, and `validateBackdrop` checks a definition without a GPU. - **Shader helpers** — `hash21`, `noise2`, `fbm2`, the eased pointer position, and every param by its own name. - **WebGPU and WebGL2** — snippets are translated for WebGL2, and `failure(name)` says why a backdrop does not draw on this device. ## Good for - **Space shooters** — a parallax starfield over a nebula, with no tiles to scroll and no edge to run out of. - **Platformers and runners** — a sky gradient pinned to the screen behind the level, with clouds or a sunset as another layer. - **Title screens and menus** — a background painting, layered skies, and fades and tweens to bring each layer on. - **Mood overlays** — a fog or tint layer that eases in over the scene and out again. - **Tools and generated content** — a snippet written by a tool or a model is validated before it reaches the screen. ## Make it yours The pack has no options: everything is per `add` call. You choose which backdrop packs to compose, pass params and colours to each `add`, change them live, and fade or tween them as the game goes. A backdrop may declare up to sixteen params and four colours. Two very different uses: a space shooter stacks `sky` in deep blue, then `nebula`, then a `stars` field whose drift keeps it moving while the camera is still; a title screen sets its painting as the background, defines a shader sky of its own for that one scene, and fades a second layer in after a few seconds. ## A quick look A sky with stars over it, retinted, tweened and faded, over a background picture: ```ts game.backdrop.add('sky', { curve: 1.3 }, { top: '#0b1a3a', bottom: '#2a4a8a' }); const stars = game.backdrop.add('stars', { density: 1.2, drift: 0.1 }); stars.setColor('tint', '#ffe9c4'); // live await stars.tween({ drift: 0.6 }, { duration: 3, ease: 'easeInOutSine' }); // on the sim clock stars.hide({ duration: 4 }); // fade out game.backdrop.background('title-art', 'cover'); // a picture under the stack ``` ## Works with - `backdrop-sky` and `backdrop-stars` — the gradient and the parallax starfield, both in the core bundles beside this pack. - `backdrop-nebula`, `backdrop-aurora`, `backdrop-sunset`, `backdrop-clouds`, `backdrop-raster-bands` and `backdrop-environments` — more looks to stack. - `core-2d`, `core-3d` and `core-vector` — include this pack, so most games have it already. - `title-screen` — defines and stacks its skies through this runtime. - `backdrop-trippatron` — one reactive arena background with its own pass, for a surface that ripples with impacts. - `sky-3d` and `skymax` — for a 3D sky with a time of day. ## Good to know - Each backdrop is a full-screen pass and noise is not free: two or three layers is the sensible ceiling. - A backdrop reads only the camera, the clock, the pointer and the background picture; it cannot see sprites, the world or lights. - Colours are set, not tweened, and tweens and fades step with the simulation (60 a second by default), not the display. - Output must be premultiplied or stacking blends wrongly, and a compile error shows in the console and `failure(name)`, not when `add` is called. --- ## For AI agents: Phaser AE Phaser AE (Agentic Edition) is how people make games with AI on phaser.io. 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