Plots and drawings

plots: [{
  title?,         // legend name
  values,         // Array<number | null>, one per bar
  color?,         // hex or rgba()
  width?,         // line width in px
  style?,         // 'line' (default) | 'dashed' | 'dotted' | 'histogram'
  negativeColor?, // histogram bars below zero
}]

function compute(bars, inputs, hp) {
  const closes = bars.map(b => b.c);
  const fast = hp.ema(closes, 12), slow = hp.ema(closes, 26);
  const diff = fast.map((v, i) => v == null || slow[i] == null ? null : v - slow[i]);
  return {
    plots: [
      { title: 'MACD', values: diff, style: 'histogram', color: '#26a69a', negativeColor: '#ef5350' },
      { title: 'Signal', values: hp.ema(diff, 9), color: '#f59e0b', style: 'dashed' },
    ],
    guides: [0],
  };
}

boxes: [{ x1, y1, x2, y2, bg?, border?, borderWidth?, text?, textColor? }]

labels: [{ x, y, text, color?, textColor?, anchor?, size? }]
// anchor: 'up' (bubble above the point) | 'down' | 'left' | 'right' | 'center'

lines: [{ x1, y1, x2, y2, color?, width?, style? }]
// style: 'solid' (default) | 'dashed' | 'dotted'

markers: [{ x, y, shape?, color?, text?, textColor? }]
// y: a number, or 'above' / 'below' to anchor to the bar's high / low
// shape: 'triangle-up' | 'triangle-down' | 'circle' | 'square' | 'arrow-up' | 'arrow-down'

bg: [{ x1, x2, color }]   // a vertical band across the full pane height

function compute(bars) {
  const markers = [];
  for (let i = 1; i < bars.length; i += 1) {
    if (bars[i].c > bars[i - 1].h) markers.push({ x: i, y: 'below', shape: 'triangle-up', color: '#26a69a' });
    if (bars[i].c < bars[i - 1].l) markers.push({ x: i, y: 'above', shape: 'triangle-down', color: '#ef5350' });
  }
  return { plots: [], markers: markers.slice(-500) };
}