Thermal Camera - Inconsistent Background Behavior

[adlarkin]

Following the thermal camera tutorial results in a different background appearance between the ign-rendering3 and ign-rendering4 branches.

Here's the result of running ign gazebo thermal_camera.sdf with ign-rendering3:

Here's the result of running ign gazebo thermal_camera.sdf with ign-rendering4:

It appears that this behavior is caused by different visibility flags being assigned to non-temperature visuals. For example, if the following change is made to Ogre2ThermalCamera.cc, it shows that non-temperature visuals have a visibility flag of 0x3fffffff in ign-rendering4, but are 0x0fffffff in ign-rendering3:

diff --git a/ogre2/src/Ogre2ThermalCamera.cc b/ogre2/src/Ogre2ThermalCamera.cc
index 012e0f23..9fddf0ad 100644
--- a/ogre2/src/Ogre2ThermalCamera.cc
+++ b/ogre2/src/Ogre2ThermalCamera.cc
@@ -231,6 +231,11 @@ void Ogre2ThermalCameraMaterialSwitcher::preRenderTargetUpdate(
           }
         }
       }
+      else
+      {
+        ignerr << "non temp object, has the following visibility flags: " << std::hex
+          << item->getVisibilityFlags() << "\n";
+      }
     }
     itor.moveNext();
   }

Since the thermal camera's visibility flag is 0x10000000, this means that the background (which doesn't have a temperature visual) is visible in ign-rendering4, but not in ign-rendering3 (a visual can be seen by the thermal camera if the result of ANDing the visual's visibility flag with the thermal camera's visibility flag is a flag with non-zero bits).

[chapulina]

Addressed in #189