sliders: implement color coding for clarity

app/widget/slider/base/sliderbase.h

@@ -55,6 +55,11 @@ public:
     UpdateLabel();
   }
 
+  void SetColor(const QColor &c)
+  {
+    label_->SetColor(c);
+  }
+
 public slots:
   void ShowEditor();
 

app/widget/slider/base/sliderlabel.cpp

@@ -27,7 +27,8 @@
 namespace olive {
 
 SliderLabel::SliderLabel(QWidget *parent) :
-  QLabel(parent)
+  QLabel(parent),
+  override_color_enabled_(false)
 {
   QPalette p = palette();
 
@@ -52,6 +53,26 @@ SliderLabel::SliderLabel(QWidget *parent) :
   setContextMenuPolicy(Qt::CustomContextMenu);
 }
 
+void SliderLabel::SetColor(const QColor &c)
+{
+  // Prevent infinite loop in changeEvent when we set the stylesheet
+  override_color_enabled_ = false;
+  override_color_ = c;
+
+  // Different colors will look different depending on the theme (light/dark mode). We abstract
+  // that away here so that other classes can simply choose a color and we will handle making it
+  // more legible based on the background
+  QColor adjusted;
+  if (palette().window().color().lightness() < 128) {
+    adjusted = override_color_.lighter(150);
+  } else {
+    adjusted = override_color_.darker(150);
+  }
+
+  setStyleSheet(QStringLiteral("color: %1").arg(adjusted.name()));
+  override_color_enabled_ = true;
+}
+
 void SliderLabel::mousePressEvent(QMouseEvent *e)
 {
   if (e->button() == Qt::LeftButton) {
@@ -81,4 +102,13 @@ void SliderLabel::focusInEvent(QFocusEvent *event)
   }
 }
 
+void SliderLabel::changeEvent(QEvent *event)
+{
+  QWidget::changeEvent(event);
+
+  if (override_color_enabled_ && event->type() == QEvent::StyleChange) {
+    SetColor(override_color_);
+  }
+}
+
 }

app/widget/slider/base/sliderlabel.h

@@ -33,6 +33,8 @@ class SliderLabel : public QLabel
 public:
   SliderLabel(QWidget* parent);
 
+  void SetColor(const QColor &c);
+
 protected:
   virtual void mousePressEvent(QMouseEvent *e) override;
 
@@ -40,6 +42,8 @@ protected:
 
   virtual void focusInEvent(QFocusEvent *event) override;
 
+  virtual void changeEvent(QEvent *event) override;
+
 signals:
   void LabelPressed();
 
@@ -51,6 +55,10 @@ signals:
 
   void ChangeSliderType();
 
+private:
+  bool override_color_enabled_;
+  QColor override_color_;
+
 };
 
 }