---
title: "Destructible cover"
package: "@phaser-ae/destructible-cover"
tier: Pro
version: 3.0.0-3
released: 2026-10-14
updated: 2026-10-20
description: "Shields, walls and breakable terrain made of cells with their own materials and health, that shots trace through and explosions chip away by stencil, radius or rectangle."
url: https://phaser.io/packs/destructible-cover
site: Phaser - https://phaser.io
---

# Destructible cover

Cover that wears away the way arcade bunkers do: masks of square cells, each with its own material and health, that
shots trace through and explosions chip away. Shapes, materials and blast patterns are all yours to author.

## What it does

A piece of cover is a mask: rows of characters, one per cell, each character standing for a material with hit points, an
optional blast resistance, or no damage at all. You lay out as many pieces as you need, of any shape and size. When a
shot moves, you trace its box or point from where it was to where it is, and get back the earliest contact with a cell
that still stands. Holes are real: a shot passes straight through a gap an earlier shot opened.

Damage comes three ways. `splat` erodes by a stencil, a small mask of its own, so a shot blows a ragged hole out of a
shield rather than one cell or a perfect circle. `damage` hits the contacted cell and spreads to neighbours within a
radius, divided by each one's blast resistance. `eraseRect` damages everything under a rectangle, for an enemy marching
through a shield. Indestructible cells block traces and never take damage, so a frame can hold its shape while the brick
inside crumbles.

For drawing, `runs()` returns horizontal runs of cells with the same material and health, so a shield is a handful of
rectangles rather than hundreds of cells, and `revision` changes on every hit so you redraw only when something broke.
Snapshots save the state of every cell, and the whole thing runs without a renderer.

## Features

- **Masks and materials** — cover authored as rows of characters, each character a material with hit points, blast
  resistance or `indestructible`.
- **Swept traces** — `traceBox` and `trace` find the earliest contact with a surviving cell along a shot's path, and
  only visit the cells under it, so small shots against large masks stay cheap.
- **Three kinds of damage** — stencil splats, radius blasts scaled by resistance, and rectangle erasure.
- **Arcade presets** — `INVADERS_SHIELD_MASK`, the classic 22 by 16 shield with its off-centre notch, and
  `INVADERS_PLAYER_SPLAT` and `INVADERS_ALIEN_SPLAT`, the ragged shot explosions, taken from the original game's data.
- **Evenly spaced bunkers** — `bunkerPreset` places any number of bunkers of any mask across a screen.
- **Cheap drawing** — `runs()` merges cells into horizontal runs, and `revision` tells you when to redraw.
- **Snapshot and reset** — save, restore and reset every cell's health.

## Good for

- **Fixed shooters with bunkers** in the style of Space Invaders, with shields eroded by player and alien shots and by
  invaders marching through.
- **Castle and fortress walls** that crumble brick by brick behind an indestructible frame.
- **Top-down shooters** with cover that wears away as the fight goes on.
- **Artillery and digging shots**, where a projectile bites a shaped hole out of a wall.
- **Armour plates** of several materials, where heavy plating shrugs off splash that destroys brick.

## Make it yours

Each definition has an id, a position, a cell size, a mask and the materials its characters stand for. There is no limit
on how many definitions, shapes, materials or stencils you use, and contact sizes and damage amounts are the caller's to
choose per shot. `bunkerPreset` takes the count, world width, height on screen, cell size, hit points, mask, left edge
and spacing.

Two materially different uses: the four classic shields, eroded by the original shot stencils and erased where the
invaders march; and a fortress of steel that never breaks, armour with three hit points and a blast resistance of two,
and one-hit brick, all worn down by radius blasts.

## A quick look

Four bunkers, a shot traced upward, a splat where it hit, and the shields drawn as runs:

```ts
const dc = game.destructibleCover;
const cover = dc.createDestructibleCover(dc.bunkerPreset({ count: 4, worldWidth: 224, y: 192, left: 32, pitch: 45 }));
const hit = cover.traceBox({ x: 30.5, y: 210 }, { x: 30.5, y: 206 }, 0.5, 2);   // a 1x4 shot moving up
if (hit) cover.splat({ x: hit.at.x, y: hit.at.y - 4 }, { mask: [...dc.INVADERS_PLAYER_SPLAT] });
for (const r of cover.runs()) drawRect(r.x, r.y, r.length * r.size, r.size, r.material, r.hp);
```

## Works with

- `marching-fleet` — uses this pack for the shields of its marching invader fleet.
- `render-auto`, `world-screen` and `typography` — enough to draw cover, a screen and a score.

## Good to know

- Cells are axis-aligned squares and do not collapse or fall: there is no physical crumbling.
- It is not for continuous deformable terrain meshes.
- Masks must be non-empty and rectangular, at most a million cells each.
- A snapshot only restores into definitions with the same mask shapes.

---

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