Workshop › Pinball › Step 13 of 42

Small steps and a speed limit

What we are doing

A fast ball can jump over a thin wall between two frames. So each frame is split into four small steps, and the speed is capped at MAX_SPEED.

```js
const SUB = 4 // physics steps per frame
const MAX_SPEED = 18

function step() {
  ball.vy += GRAVITY / SUB
  ball.x += ball.vx / SUB
  ball.y += ball.vy / SUB
  for (const w of WALLS) hitSegment(w[0], w[1], w[2], w[3], 0.5)
}

function update() {
  for (let i = 0; i < SUB; i++) step()
  const speed = Math.hypot(ball.vx, ball.vy)
  if (speed > MAX_SPEED) {
    ball.vx *= MAX_SPEED / speed
    ball.vy *= MAX_SPEED / speed
  }
}
```

What it means

step() is the old update with everything divided by SUB: a quarter of the gravity and a quarter of the move.
for (let i = 0; i < SUB; i++) step() runs it four times per frame.
Math.hypot(vx, vy) is the ball's speed; if it is above the limit, both parts are scaled down by the same factor, so the direction stays the same.

Your turn

Under GRAVITY write SUB and MAX_SPEED.
Replace the whole update function with step and the new update.

Skills: Velocity and gravity, Loops

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