explodorama / files / src / ui / spatial.ts
spatial.ts
| 1 | /** |
| 2 | * Moving focus between on-screen controls with a d-pad or stick (controller support, stage 1): |
| 3 | * the neighbour in the pressed direction, judged by where the rectangles are. Pure, so the caller |
| 4 | * measures the elements (`getBoundingClientRect`) and this only does the geometry. |
| 5 | */ |
| 6 | /** One step along an axis: back, none, forward. */ |
| 7 | export type Step = -1 | 0 | 1 |
| 8 | |
| 9 | export interface FocusRect { |
| 10 | x: number |
| 11 | y: number |
| 12 | w: number |
| 13 | h: number |
| 14 | } |
| 15 | |
| 16 | /** |
| 17 | * The index of the best rectangle in direction (dx, dy) from `rects[current]`, or `current` if |
| 18 | * none lies that way. A candidate counts when its centre is strictly past the current centre on |
| 19 | * every axis the direction uses. Score = distance along the direction + 2 x distance sideways |
| 20 | * (lower wins; a tie goes to the lower index), so a button straight along the row beats a nearer |
| 21 | * one a row off. An empty list gives -1; a `current` that is -1 or out of range gives 0; (0, 0) |
| 22 | * gives `current`. For a diagonal, both axes count as "along" and nothing is sideways. |
| 23 | */ |
| 24 | export function nextFocus(rects: FocusRect[], current: number, dx: Step, dy: Step): number { |
| 25 | if (rects.length === 0) return -1 |
| 26 | const cur = rects[current] |
| 27 | if (cur === undefined) return 0 |
| 28 | const cx = cur.x + cur.w / 2 |
| 29 | const cy = cur.y + cur.h / 2 |
| 30 | if (dx === 0 && dy === 0) return current |
| 31 | let best = current |
| 32 | let bestScore = Infinity |
| 33 | rects.forEach((r, i) => { |
| 34 | if (i === current) return |
| 35 | const ox = r.x + r.w / 2 - cx |
| 36 | const oy = r.y + r.h / 2 - cy |
| 37 | if (dx !== 0 && ox * dx <= 0) return |
| 38 | if (dy !== 0 && oy * dy <= 0) return |
| 39 | const along = (dx !== 0 ? Math.abs(ox) : 0) + (dy !== 0 ? Math.abs(oy) : 0) |
| 40 | const side = (dx === 0 ? Math.abs(ox) : 0) + (dy === 0 ? Math.abs(oy) : 0) |
| 41 | const score = along + 2 * side |
| 42 | if (score < bestScore) { |
| 43 | bestScore = score |
| 44 | best = i |
| 45 | } |
| 46 | }) |
| 47 | return best |
| 48 | } |