implemented percentage and decibel view modes for slider

A slider can now hold a float value and display it in the UI converted to
either a percentage or a decibel (still returning a linear float value
programmatically for the rest of the code).

app/widget/slider/floatslider.cpp

@@ -20,8 +20,11 @@
 
 #include "floatslider.h"
 
+#include <QAudio>
+
 FloatSlider::FloatSlider(QWidget *parent) :
-  SliderBase(kFloat, parent)
+  SliderBase(kFloat, parent),
+  display_type_(kNormal)
 {
   connect(this, SIGNAL(ValueChanged(QVariant)), this, SLOT(ConvertValue(QVariant)));
 }
@@ -53,17 +56,108 @@ void FloatSlider::SetDecimalPlaces(int i)
   UpdateLabel(Value());
 }
 
+void FloatSlider::SetDisplayType(const FloatSlider::DisplayType &type)
+{
+  display_type_ = type;
+
+  UpdateLabel(Value());
+}
+
 QString FloatSlider::ValueToString(const QVariant &v)
 {
-  return QString::number(v.toDouble(), 'f', decimal_places_);
+  double val = v.toDouble();
+
+  switch (display_type_) {
+  case kNormal:
+    // Do nothing, skip to the return string at the end
+    break;
+  case kDecibel:
+  {
+    // Convert to decibels and return dB formatted string
+    qreal decibels = QAudio::convertVolume(val, QAudio::LinearVolumeScale, QAudio::DecibelVolumeScale);
+    return QStringLiteral("%1 dB").arg(QString::number(decibels, 'f', decimal_places_));
+  }
+  case kPercentage:
+    // Multiply value by 100 for user-friendly percentage
+    val *= 100.0;
+    return QStringLiteral("%1%").arg(QString::number(val, 'f', decimal_places_));
+  }
+
+  return QString::number(val, 'f', decimal_places_);
 }
 
 QVariant FloatSlider::StringToValue(const QString &s, bool *ok)
 {
-  // Allow both floats and integers for either modes
+  switch (display_type_) {
+  case kNormal:
+    // Do nothing, skip to the return string at the end
+    break;
+  case kDecibel:
+  {
+    bool valid;
+
+    // Remove any instance of "dB" in the string
+    QString decibel_number = s;
+    decibel_number.replace("dB", "", Qt::CaseInsensitive);
+
+    // See if we can get a decimal number out of this
+    qreal decibels = decibel_number.toDouble(&valid);
+
+    if (ok) *ok = valid;
+
+    if (valid) {
+      // Convert from decibel scale to linear decimal
+      return QAudio::convertVolume(decibels, QAudio::DecibelVolumeScale, QAudio::LinearVolumeScale);
+    }
+
+    break;
+  }
+  case kPercentage:
+  {
+    bool valid;
+
+    QString percent_number = s;
+    percent_number.replace("%", "", Qt::CaseInsensitive);
+
+    // Try to get double value
+    double val = percent_number.toDouble(&valid);
+
+    if (ok) *ok = valid;
+
+    // If we could get it, convert back to a 0.0 - 1.0 value and return
+    if (valid) {
+      return val * 0.01;
+    }
+
+    break;
+  }
+  }
+
+  // Just try to convert the string to a double
   return s.toDouble(ok);
 }
 
+double FloatSlider::AdjustDragDistanceInternal(const double &start, const double &drag)
+{
+  switch (display_type_) {
+  case kNormal:
+    // No change here
+    break;
+  case kDecibel:
+  {
+    qreal current_db = QAudio::convertVolume(start, QAudio::LinearVolumeScale, QAudio::DecibelVolumeScale);
+    current_db += drag;
+    qreal adjusted_linear = QAudio::convertVolume(current_db, QAudio::DecibelVolumeScale, QAudio::LinearVolumeScale);
+
+    return adjusted_linear - start;
+  }
+  case kPercentage:
+    return drag * 0.01;
+  }
+
+  return SliderBase::AdjustDragDistanceInternal(start, drag);
+}
+
 void FloatSlider::ConvertValue(QVariant v)
 {
   emit ValueChanged(v.toDouble());