+void View::calculate_tick_spacing()
+{
+ const double SpacingIncrement = 10.0f;
+ const double MinValueSpacing = 25.0f;
+
+ // Figure out the highest numeric value visible on a label
+ const QSize areaSize = viewport_->size();
+ const double max_time = max(fabs(offset_),
+ fabs(offset_ + scale_ * areaSize.width()));
+
+ double min_width = SpacingIncrement;
+ double label_width, tick_period_width;
+
+ QFontMetrics m(QApplication::font());
+
+ do {
+ const double min_period = scale_ * min_width;
+
+ const int order = (int)floorf(log10f(min_period));
+ const double order_decimal = pow(10.0, order);
+
+ // Allow for a margin of error so that a scale unit of 1 can be used.
+ // Otherwise, for a SU of 1 the tick period will almost always be below
+ // the min_period by a small amount - and thus skipped in favor of 2.
+ // Note: margin assumes that SU[0] and SU[1] contain the smallest values
+ double tp_margin = (ScaleUnits[0] + ScaleUnits[1]) / 2.0;
+ double tp_with_margin;
+ unsigned int unit = 0;
+
+ do {
+ tp_with_margin = order_decimal * (ScaleUnits[unit++] + tp_margin);
+ } while (tp_with_margin < min_period && unit < countof(ScaleUnits));
+
+ tick_period_ = order_decimal * ScaleUnits[unit - 1];
+ tick_prefix_ = (order - pv::util::FirstSIPrefixPower) / 3;
+
+ // Precision is the number of fractional digits required, not
+ // taking the prefix into account (and it must never be negative)
+ tick_precision_ = std::max((int)ceil(log10f(1 / tick_period_)), 0);
+
+ tick_period_width = tick_period_ / scale_;
+
+ const QString label_text =
+ format_time(max_time, tick_prefix_, time_unit_, tick_precision_);
+
+ label_width = m.boundingRect(0, 0, INT_MAX, INT_MAX,
+ Qt::AlignLeft | Qt::AlignTop, label_text).width() +
+ MinValueSpacing;
+
+ min_width += SpacingIncrement;
+
+ } while (tick_period_width < label_width);
+}
+