Workshop › Mario-style Platformer › Step 4 of 37

What is solid?

What we are doing

Everything the player does will ask one question: is this point inside a solid tile? solidAt(x, y) turns pixels into a tile and answers, including what happens outside the level.

```js
function solidAt(x, y) {
  const col = Math.floor(x / TILE)
  const row = Math.floor(y / TILE)
  if (col < 0 || col >= COLS) return true // invisible walls at both ends of the level
  if (row < 0 || row >= ROWS) return false // open sky above, bottomless pits below
  const tile = LEVEL[row][col]
  return tile === '#' || tile === 'B'
}
```

What it means

Math.floor(x / TILE) turns a pixel into a column: pixel 100 is in column 3 (100 / 32 = 3.1, floored).
Outside the level on the left or right: solid. Above or below: air.
Inside, the answer is whether the tile is ground or brick.

Your turn

Above function draw() { write solidAt, with an empty line between them.

Skills: Collision detection, Functions

← Draw the tiles Is a box touching anything? →

All steps