Workshop › Rhythm Lanes › Step 7 of 35

From text to notes

What we are doing

The game needs notes, not text. Every 1 in the chart becomes a note object { lane, time, hit }, where time is the frame at which it must be hit.

```js
const STEP = 15 // frames between rows of the chart (an eighth note at 120 beats a minute)
const LEAD = 120 // frames before the first row reaches the line

let notes // { lane, time, hit }

function reset() {
  notes = []
  CHART.forEach((row, i) => {
    for (let lane = 0; lane < LANES; lane++) if (row[lane] === '1') notes.push({ lane, time: LEAD + i * STEP, hit: false })
  })
}

reset()
draw()
```

What it means

CHART.forEach((row, i) => ...) runs once for each row: row is its text, i its number.
The for loop looks at the row's four characters; each '1' pushes a note onto notes.
A note of row i must be hit at frame LEAD + i * STEP. { lane, ... } is short for { lane: lane, ... }.
reset() builds the notes once, before the first draw().

Your turn

Under HIT_Y, write STEP and LEAD.
Under CHART, after an empty line, write let notes and reset.
At the bottom, write reset() above draw().

Skills: Arrays and objects, Loops

← The song as text The clock decides where →

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