scopes: only update if visible

Updating scopes can require heavy processing so we limit updates to only
when the scope is visible

app/widget/scope/histogram/histogram.cpp

@@ -49,7 +49,9 @@ void HistogramScope::SetBuffer(Frame* frame)
 {
   buffer_ = frame;
 
-  StartUpdate();
+  if (isVisible()) {
+    StartUpdate();
+  }
 }
 
 void HistogramScope::FinishedProcessing(QVector<double> red, QVector<double> green, QVector<double> blue)
@@ -111,6 +113,13 @@ void HistogramScope::StartUpdate()
   }
 }
 
+void HistogramScope::showEvent(QShowEvent* e)
+{
+  ManagedDisplayWidget::showEvent(e);
+
+  StartUpdate();
+}
+
 HistogramScopeWorker::HistogramScopeWorker() :
   cancelled_(false)
 {

app/widget/scope/histogram/histogram.h

@@ -78,6 +78,8 @@ protected:
 
   virtual void ColorProcessorChangedEvent() override;
 
+  virtual void showEvent(QShowEvent* e) override;
+
 private:
   void StartUpdate();
 

app/widget/scope/waveform/waveform.cpp

@@ -49,6 +49,13 @@ void WaveformScope::SetBuffer(Frame *frame)
   UploadTextureFromBuffer();
 }
 
+void WaveformScope::showEvent(QShowEvent* e)
+{
+  ManagedDisplayWidget::showEvent(e);
+
+  UploadTextureFromBuffer();
+}
+
 void WaveformScope::initializeGL()
 {
   ManagedDisplayWidget::initializeGL();
@@ -93,7 +100,7 @@ void WaveformScope::paintGL()
 
 void WaveformScope::UploadTextureFromBuffer()
 {
-  if (!buffer_) {
+  if (!buffer_ || !isVisible()) {
     return;
   }
 

app/widget/scope/waveform/waveform.h

@@ -45,6 +45,8 @@ protected:
 
   virtual void paintGL() override;
 
+  virtual void showEvent(QShowEvent* e) override;
+
 private:
   void UploadTextureFromBuffer();