Workshop › Scorched Earth-style Artillery › Step 11 of 23

Craters

What we are doing

An explosion digs a round hole. For each column within the blast, the bottom of a circle of radius 30 is found; if it is lower than the ground there, the ground drops to it. Holes never go through the bottom of the screen.

```js
// Blow a round hole in the ground and hurt the tanks nearby.
  for (let cx = Math.floor(x - BLAST); cx <= x + BLAST; cx++) {
    if (cx < 0 || cx >= W) continue
    const bottom = y + Math.sqrt(BLAST * BLAST - (cx - x) ** 2)
    if (bottom > ground[cx]) ground[cx] = Math.min(H - 2, bottom)
  }
```

What it means

The circle: at a sideways distance d from the middle, its bottom is √(r² − d²) below the middle (Pythagoras).
Ground only goes down, never up: a blast in the air above a hill does not fill anything.
continue skips columns off the canvas.

Your turn

Above explode, write the comment.
At the top of explode, dig the hole.

Skills: Velocity and gravity, Arrays and objects

← Boom Falling tanks →

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