draw method

Implementation

void draw(Canvas canvas) {
  // The highlighted column is filled first so the grid lines and events draw
  // on top of it (it emphasizes the column without obscuring its content).
  _drawHighlight(canvas);

  // vertical lines can be drawn instantly
  for (var line in vLines) {
    line.draw(canvas, vPaint);
  }

  // The 30-minute lines fade in past zoom 1, the 15/45-minute lines past
  // zoom 2. These thresholds are cheap to recompute each frame and also gate
  // line visibility below.
  final double zoom = manager.controller.zoom;
  final double color2 = (zoom - 1).clamp(0.0, 1.0).toDouble();
  final double color3 = (zoom - 2).clamp(0.0, 1.0).toDouble();

  // Recolour the cached paints only when the zoom actually changed, reusing
  // the same Paint objects across frames instead of allocating two per frame
  // (#25 / D7).
  if (zoom != _cachedZoom) {
    div2Paint.color = Color.fromARGB((color2 * 60).toInt(), 255, 255, 255);
    div3Paint.color = Color.fromARGB((color3 * 30).toInt(), 255, 255, 255);
    _cachedZoom = zoom;
  }

  // draw lines
  for (int i = 0; i < hLines.length; i++) {
    if ((i + 1) % 4 == 0) {
      // hour
      hLines[i].draw(canvas, vPaint);
    } else if ((i + 1) % 2 == 0 && color2 != 0) {
      // half an hour
      hLines[i].draw(canvas, div2Paint);
    } else if (color3 != 0) {
      // 15 and 45 minutes
      hLines[i].draw(canvas, div3Paint);
    }
  }
}