Method arcTo

app/src/UI/Widgets/PainterContext.cpp:1041–1108

* @brief Adds a Canvas2D-style arcTo: tangent arc of radius r between two segments. */

 * @brief Adds a Canvas2D-style arcTo: tangent arc of radius r between two segments.
 */
void Widgets::PainterContext::arcTo(qreal x1, qreal y1, qreal x2, qreal y2, qreal r)
{
  if (r < 0.0)
    return;

  if (m_path.isEmpty()) {
    m_path.moveTo(x1, y1);
    return;
  }

  const QPointF p0 = m_path.currentPosition();
  const qreal v1x  = p0.x() - x1;
  const qreal v1y  = p0.y() - y1;
  const qreal v2x  = x2 - x1;
  const qreal v2y  = y2 - y1;
  const qreal len1 = std::hypot(v1x, v1y);
  const qreal len2 = std::hypot(v2x, v2y);
  if (qFuzzyIsNull(len1) || qFuzzyIsNull(len2) || qFuzzyIsNull(r)) {
    m_path.lineTo(x1, y1);
    return;
  }

  const qreal cos_a = (v1x * v2x + v1y * v2y) / (len1 * len2);
  const qreal a     = std::acos(qBound<qreal>(-1.0, cos_a, 1.0));
  if (qFuzzyCompare(a, M_PI) || qFuzzyIsNull(a)) {
    m_path.lineTo(x1, y1);
    return;
  }

  const qreal d       = r / std::tan(a * 0.5);
  const qreal invLen1 = 1.0 / len1;
  const qreal invLen2 = 1.0 / len2;
  const qreal n1x     = v1x * invLen1;
  const qreal n1y     = v1y * invLen1;
  const qreal n2x     = v2x * invLen2;
  const qreal n2y     = v2y * invLen2;
  const qreal tx1     = x1 + n1x * d;
  const qreal ty1     = y1 + n1y * d;
  const qreal tx2     = x1 + n2x * d;
  const qreal ty2     = y1 + n2y * d;

  const qreal sx = n1x + n2x;
  const qreal sy = n1y + n2y;
  const qreal sl = std::hypot(sx, sy);
  if (qFuzzyIsNull(sl)) {
    m_path.lineTo(x1, y1);
    return;
  }

  const qreal cR    = r / std::sin(a * 0.5);
  const qreal invSl = 1.0 / sl;
  const qreal cX    = x1 + (sx * invSl) * cR;
  const qreal cY    = y1 + (sy * invSl) * cR;
  const qreal cross = v1x * v2y - v1y * v2x;

  m_path.lineTo(tx1, ty1);

  const qreal startAng = std::atan2(ty1 - cY, tx1 - cX);