Disable cad perpendicular/parallel buttons when snapping is disabled

And use tooltips to advise users that snapping must be enabled
before this functionality can be used.

Hopefully helps make the behaviour of these features a bit more
predictable for users

src/gui/qgsadvanceddigitizingdockwidget.cpp

@@ -30,6 +30,7 @@
 #include "qgslinestring.h"
 #include "qgsfocuswatcher.h"
 #include "qgssettings.h"
+#include "qgsproject.h"
 
 struct EdgesOnlyFilter : public QgsPointLocator::MatchFilter
 {
@@ -199,9 +200,6 @@ QgsAdvancedDigitizingDockWidget::QgsAdvancedDigitizingDockWidget( QgsMapCanvas *
 
   // set tooltips
   mConstructionModeButton->setToolTip( "<b>" + tr( "Construction mode" ) + "</b><br>(" + tr( "press c to toggle on/off" ) + ")" );
-  mPerpendicularButton->setToolTip( "<b>" + tr( "Perpendicular" ) + "</b><br>(" + tr( "press p to switch between perpendicular, parallel and normal mode" ) + ")" );
-  mParallelButton->setToolTip( "<b>" + tr( "Parallel" ) + "</b><br>(" + tr( "press p to switch between perpendicular, parallel and normal mode" ) + ")" );
-
   mDistanceLineEdit->setToolTip( "<b>" + tr( "Distance" ) + "</b><br>(" + tr( "press d for quick access" ) + ")" );
   mLockDistanceButton->setToolTip( "<b>" + tr( "Lock distance" ) + "</b><br>(" + tr( "press Ctrl + d for quick access" ) + ")" );
   mRepeatingLockDistanceButton->setToolTip( "<b>" + tr( "Continuously lock distance" ) + "</b>" );
@@ -223,6 +221,8 @@ QgsAdvancedDigitizingDockWidget::QgsAdvancedDigitizingDockWidget( QgsMapCanvas *
 
 
   updateCapacity( true );
+  connect( QgsProject::instance(), &QgsProject::snappingConfigChanged, this, [ = ] { updateCapacity( true ); } );
+
   disable();
 }
 
@@ -525,15 +525,31 @@ void QgsAdvancedDigitizingDockWidget::updateCapacity( bool updateUIwithoutChange
     return;
   }
 
+  bool snappingEnabled = QgsProject::instance()->snappingConfig().enabled();
+
   // update the UI according to new capacities
   // still keep the old to compare
 
   bool relativeAngle = mCadEnabled && newCapacities.testFlag( RelativeAngle );
   bool absoluteAngle = mCadEnabled && newCapacities.testFlag( AbsoluteAngle );
   bool relativeCoordinates = mCadEnabled && newCapacities.testFlag( RelativeCoordinates );
 
-  mPerpendicularButton->setEnabled( absoluteAngle );
-  mParallelButton->setEnabled( absoluteAngle );
+  mPerpendicularButton->setEnabled( absoluteAngle && snappingEnabled );
+  mParallelButton->setEnabled( absoluteAngle && snappingEnabled );
+
+  //update tooltips on buttons
+  if ( !snappingEnabled )
+  {
+    mPerpendicularButton->setToolTip( tr( "Snapping must be enabled to utilize perpendicular mode" ) );
+    mParallelButton->setToolTip( tr( "Snapping must be enabled to utilize parallel mode" ) );
+  }
+  else
+  {
+    mPerpendicularButton->setToolTip( "<b>" + tr( "Perpendicular" ) + "</b><br>(" + tr( "press p to switch between perpendicular, parallel and normal mode" ) + ")" );
+    mParallelButton->setToolTip( "<b>" + tr( "Parallel" ) + "</b><br>(" + tr( "press p to switch between perpendicular, parallel and normal mode" ) + ")" );
+  }
+
+
   if ( !absoluteAngle )
   {
     lockAdditionalConstraint( NoConstraint );