Fix for windows 7 and below requiring focus for mouse wheel.

src/visual/MeterCanvas.cpp

@@ -163,6 +163,7 @@ void MeterCanvas::OnMouseEnterWindow(wxMouseEvent& event) {
     InteractiveCanvas::mouseTracker.OnMouseEnterWindow(event);
     SetCursor(wxCURSOR_CROSS);
     Refresh();
+	this->SetFocus();
 }
 
 void MeterCanvas::setHelpTip(std::string tip) {

src/visual/SpectrumCanvas.cpp

@@ -259,6 +259,9 @@ void SpectrumCanvas::OnMouseReleased(wxMouseEvent& event) {
 void SpectrumCanvas::OnMouseEnterWindow(wxMouseEvent& event) {
     InteractiveCanvas::OnMouseEnterWindow(event);
     SetCursor(wxCURSOR_SIZEWE);
+	if (waterfallCanvas) {
+		waterfallCanvas->SetFocus();
+	}
 }
 
 void SpectrumCanvas::OnMouseLeftWindow(wxMouseEvent& event) {

src/visual/TuningCanvas.cpp

@@ -410,6 +410,7 @@ void TuningCanvas::OnMouseEnterWindow(wxMouseEvent& event) {
     hoverIndex = 0;
     hoverState = TUNING_HOVER_NONE;
     lastPPM = currentPPM = wxGetApp().getPPM();
+	this->SetFocus();
 }
 
 void TuningCanvas::setHelpTip(std::string tip) {

src/visual/WaterfallCanvas.cpp

@@ -852,6 +852,7 @@ void WaterfallCanvas::OnMouseLeftWindow(wxMouseEvent& event) {
 void WaterfallCanvas::OnMouseEnterWindow(wxMouseEvent& event) {
     InteractiveCanvas::OnMouseEnterWindow(event);
     SetCursor(wxCURSOR_CROSS);
+	this->SetFocus();
 }
 
 void WaterfallCanvas::OnMouseRightDown(wxMouseEvent& event) {