eeschema-gal: added EnableDepthTest() feature in GAL

common/gal/cairo/cairo_gal.cpp

@@ -1199,3 +1199,8 @@ unsigned int CAIRO_GAL::getNewGroupNumber()
 
     return groupCounter++;
 }
+
+void CAIRO_GAL::EnableDepthTest( bool aEnabled )
+{
+    
+}

common/gal/opengl/opengl_gal.cpp

@@ -2065,3 +2065,13 @@ static void InitTesselatorCallbacks( GLUtesselator* aTesselator )
     gluTessCallback( aTesselator, GLU_TESS_EDGE_FLAG,    ( void (CALLBACK*)() )EdgeCallback );
     gluTessCallback( aTesselator, GLU_TESS_ERROR,        ( void (CALLBACK*)() )ErrorCallback );
 }
+
+void OPENGL_GAL::EnableDepthTest( bool aEnabled )
+{
+    if( aEnabled )
+        glEnable( GL_DEPTH_TEST );
+    else
+    {
+        glDisable( GL_DEPTH_TEST );
+    }
+}

include/gal/cairo/cairo_gal.h

@@ -278,6 +278,8 @@ public:
         paintListener = aPaintListener;
     }
 
+    virtual void EnableDepthTest( bool aEnabled = false ) override;
+
 protected:
     virtual void drawGridLine( const VECTOR2D& aStartPoint, const VECTOR2D& aEndPoint ) override;
 

include/gal/graphics_abstraction_layer.h

@@ -988,6 +988,8 @@ public:
         depthStack.pop();
     }
 
+    virtual void EnableDepthTest( bool aEnabled = false ) {};
+
     static const double METRIC_UNIT_LENGTH;
 
 protected:

include/gal/opengl/opengl_gal.h

@@ -276,6 +276,8 @@ public:
         paintListener = aPaintListener;
     }
 
+    virtual void EnableDepthTest( bool aEnabled = false ) override;
+
     ///< Parameters passed to the GLU tesselator
     typedef struct
     {