Workshop › Mario-style Platformer › Step 11 of 37

Speed up

What we are doing

A platformer hero feels better with momentum: holding a direction builds up speed bit by bit, up to MAX_SPEED, instead of jumping to full speed at once.

```js
const ACCEL = 0.5
const MAX_SPEED = 4

function clamp(value, min, max) {
  return Math.max(min, Math.min(max, value))
}

  const input = (keys.ArrowRight ? 1 : 0) - (keys.ArrowLeft ? 1 : 0)
  if (input !== 0) player.vx += input * ACCEL
  player.vx = clamp(player.vx, -MAX_SPEED, MAX_SPEED)
  player.x += player.vx
```

What it means

clamp keeps a value between min and max.
input is 1 for right, -1 for left, 0 for neither or both.
Each frame a direction is held, vx grows by ACCEL in that direction, clamped to ±4.
x += vx moves the player sideways.

Your turn

Under MAX_FALL write ACCEL and MAX_SPEED.
Above function solidAt(x, y) { write clamp.
At the top of updatePlayer write the four lines and an empty line.

Skills: Velocity and gravity, Keyboard and mouse input

← Which keys are held? Friction →

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