feuerwerk/src/editor/music/timeView.ts

import { type Meter, ticksPerBar, ticksPerBeat } from '../../core/music/time';
import { clamp } from '../../ui';

/**
 * The time axis of the piano roll (#333), and of the song tab after it (#334), apart from Pixi so a
 * test can drive it: ticks run left to right, `x` is measured from the left edge of the area that
 * shows them. Only across; what is stacked above each other is up to the tab.
 */
export interface TimeView {
  /** Pixels from the area's left edge to tick 0. */
  panX: number;
  pxPerTick: number;
}

export const RULER_HEIGHT = 30;
/** The strip along the top of the ruler that holds the loop; a drag there sets it, below moves the start. */
export const LOOP_STRIP = 10;
/** A bar of 4/4 from 8 pixels to a 1/32 of 60. */
export const MIN_PX_PER_TICK = 0.004;
export const MAX_PX_PER_TICK = 1;
const BAR_LABEL_MIN_PX = 36;
const BEAT_MIN_PX = 6;
const GRID_MIN_PX = 5;

export function tickToX(view: TimeView, tick: number): number {
  return view.panX + tick * view.pxPerTick;
}

export function xToTick(view: TimeView, x: number): number {
  return (x - view.panX) / view.pxPerTick;
}

/** Zooms about `x`, so the tick under the pointer stays under it. */
export function zoomTime(view: TimeView, factor: number, x: number): TimeView {
  const pxPerTick = clamp(view.pxPerTick * factor, MIN_PX_PER_TICK, MAX_PX_PER_TICK);
  const tick = xToTick(view, x);
  return { panX: x - tick * pxPerTick, pxPerTick };
}

/** How far right of the area's left edge tick 0 can be panned, as a share of the area's width. */
export const TIME_LEAD = 0.5;

/**
 * Time starts at 0, but it need not stand at the left edge: a pan can take it up to half the area in,
 * to look at, with nothing to place left of it.
 */
export function clampTimePan<V extends TimeView>(view: V, width: number): V {
  const most = Math.max(0, width * TIME_LEAD);
  return view.panX > most ? { ...view, panX: most } : view;
}

/** How far past the first or the last row (a note, a track) a pan can go, as a share of the area's height. */
export const ROW_LEAD = 0.5;

/**
 * Down the area as across it: the first row can be panned up to half the height down from the top
 * edge and the last up to half the height up from the bottom, to look at, with nothing to place there.
 * Rows that fit with room to spare are not pushed up off the top.
 */
export function clampRowPan(panY: number, content: number, height: number): number {
  const lead = Math.max(0, height * ROW_LEAD);
  return clamp(panY, Math.min(0, height - lead - content), lead);
}

/** `length` ticks across `width` pixels, from tick 0. */
export function fitTime(length: number, width: number): TimeView {
  return { panX: 0, pxPerTick: clamp(width / Math.max(1, length), MIN_PX_PER_TICK, MAX_PX_PER_TICK) };
}

/** A line across the time: 0 a bar, 1 a beat, 2 a step of the grid. */
export interface TimeLine {
  tick: number;
  x: number;
  level: 0 | 1 | 2;
}

/**
 * The lines from `0` to `width` pixels, each tick only at its strongest level. Beats and the grid
 * are left out where they would stand closer than a few pixels.
 */
export function timeLines(view: TimeView, meter: Meter, grid: number, width: number): TimeLine[] {
  const levels = new Map<number, 0 | 1 | 2>();
  const from = Math.max(0, xToTick(view, 0));
  const to = xToTick(view, width);
  const spans: [number, 0 | 1 | 2, number][] = [
    [ticksPerBar(meter), 0, 0],
    [ticksPerBeat(meter), 1, BEAT_MIN_PX],
    [grid, 2, GRID_MIN_PX],
  ];
  for (const [step, level, minPx] of spans) {
    if (step * view.pxPerTick < minPx) continue;
    for (let tick = Math.ceil(from / step) * step; tick <= to; tick += step)
      if (!levels.has(tick)) levels.set(tick, level);
  }
  return [...levels]
    .map(([tick, level]) => ({ tick, x: tickToX(view, tick), level }))
    .sort((a, b) => a.tick - b.tick);
}

export type RulerPart = 'loop' | 'time';

export function rulerPartAt(y: number): RulerPart {
  return y < LOOP_STRIP ? 'loop' : 'time';
}

/**
 * The loop a drag on the loop strip leaves: from where it was pressed to `at`, or, pressed at an end
 * of `loop`, that end moved to `at`. Null where the drag spans nothing.
 */
export function draggedLoop(
  loop: { start: number; end: number },
  edge: 'start' | 'end' | null,
  from: number,
  at: number,
): { start: number; end: number } | null {
  if (edge === 'start') return { start: Math.min(at, loop.end - 1), end: loop.end };
  if (edge === 'end') return { start: loop.start, end: Math.max(at, loop.start + 1) };
  return at === from ? null : { start: Math.min(at, from), end: Math.max(at, from) };
}

/** Every `n`-th bar gets its number on the ruler, `n` a power of two so the numbers never overlap. */
export function barLabelStep(view: TimeView, meter: Meter): number {
  const barPx = ticksPerBar(meter) * view.pxPerTick;
  let n = 1;
  while (n * barPx < BAR_LABEL_MIN_PX && n < 1024) n *= 2;
  return n;
}