Add support for anisotropic filtering in Canvas

simgear/canvas/Canvas.cxx

@@ -691,6 +691,10 @@ namespace canvas
       {
         _sampling_dirty = true;
       }
+      else if( name == "anisotropy" )
+      {
+        _texture.setMaxAnisotropy( node->getFloatValue() );
+      }
       else if( name == "additive-blend" )
       {
         _texture.useAdditiveBlend( node->getBoolValue() );

simgear/canvas/ODGauge.cxx

@@ -201,6 +201,12 @@ namespace canvas
     updateSampling();
   }
 
+  //----------------------------------------------------------------------------
+  void ODGauge::setMaxAnisotropy(float anis)
+  {
+    texture->setMaxAnisotropy(anis);
+  }
+
   //----------------------------------------------------------------------------
   void ODGauge::setRender(bool render)
   {

simgear/canvas/ODGauge.hxx

@@ -109,6 +109,8 @@ namespace canvas
                         int coverage_samples = 0,
                         int color_samples = 0 );
 
+      void setMaxAnisotropy(float anis);
+
       /**
        * Enable/Disable updating the texture (If disabled the contents of the
        * texture remains with the outcome of the last rendering pass)