Fix transparency of RobotLinks (ros-visualization#1751)

If a RobotLink has multiple visuals with different alpha values,
only the last one was actually used (stored in material_alpha_).
Instead, store the original material and use alpha from there.

src/rviz/robot/robot_link.cpp

@@ -167,7 +167,6 @@ RobotLink::RobotLink( Robot* robot,
 , collision_node_( NULL )
 , trail_( NULL )
 , axes_( NULL )
-, material_alpha_( 1.0 )
 , robot_alpha_(1.0)
 , only_render_depth_(false)
 , using_color_( false )
@@ -385,7 +384,8 @@ void RobotLink::updateAlpha()
     else
     {
       Ogre::ColourValue color = material->getTechnique(0)->getPass(0)->getDiffuse();
-      color.a = robot_alpha_ * material_alpha_ * link_alpha;
+      const float material_alpha = original->getTechnique(0)->getPass(0)->getDiffuse().a;
+      color.a = robot_alpha_ * material_alpha * link_alpha;
       material->setDiffuse( color );
 
       if ( color.a < 0.9998 )
@@ -473,8 +473,6 @@ Ogre::MaterialPtr RobotLink::getMaterialForLink( const urdf::LinkConstSharedPtr&
     const urdf::Color& col = visual->material->color;
     mat->getTechnique(0)->setAmbient(col.r * 0.5, col.g * 0.5, col.b * 0.5);
     mat->getTechnique(0)->setDiffuse(col.r, col.g, col.b, col.a);
-
-    material_alpha_ = col.a;
   }
   else
   {
@@ -650,20 +648,19 @@ void RobotLink::createEntityForGeometryElement(const urdf::LinkConstSharedPtr& l
 
       if (material_name == "BaseWhite" || material_name == "BaseWhiteNoLighting")
       {
-        sub->setMaterialName(default_material_name_);
+        original = default_material_;
       }
       else
       {
-        // Need to clone here due to how selection works.  Once selection id is done per object and not per material,
-        // this can go away
-        std::stringstream ss;
-        ss << material_name << count++ << "Robot";
-        std::string cloned_name = ss.str();
-        sub->getMaterial()->clone(cloned_name);
-        sub->setMaterialName(cloned_name);
+        original = sub->getMaterial();
       }
 
-      materials_[sub] = sub->getMaterial();
+      // create a new material copy for each instance of a RobotLink to allow modification per link
+      active = Ogre::MaterialPtr(new Ogre::Material(
+          nullptr, material_name, 0, Ogre::ResourceGroupManager::DEFAULT_RESOURCE_GROUP_NAME));
+      *active = *original;
+      sub->setMaterial(active);
+      materials_[sub] = std::make_pair(active, original);
     }
   }
 }

src/rviz/robot/robot_link.h

@@ -199,7 +199,6 @@ private Q_SLOTS:
 
   Axes* axes_;
 
-  float material_alpha_; ///< If material is not a texture, this saves the alpha value set in the URDF, otherwise is 1.0.
   float robot_alpha_; ///< Alpha value from top-level robot alpha Property (set via setRobotAlpha()).
 
   bool only_render_depth_;