Disable shadows when viewing point cloud markers (#720)

* Prevent point cloud markers from casting shadows
* Build point cloud example on macOS
- Allow the point cloud standalone example to build on macOS.

---------

Signed-off-by: Rhys Mainwaring <rhys.mainwaring@me.com>
Co-authored-by: Ian Chen <ichen@openrobotics.org>
(cherry picked from commit 308ceaf)
Signed-off-by: Ian Chen <ichen@openrobotics.org>

# Conflicts:
#	examples/standalone/point_cloud/CMakeLists.txt

Author: srmainwaring

examples/standalone/point_cloud/CMakeLists.txt

@@ -2,7 +2,8 @@ cmake_minimum_required(VERSION 3.10.2 FATAL_ERROR)
 
 project(gz-gui-point-cloud-example)
 
-if(${CMAKE_SYSTEM_NAME} STREQUAL "Linux")
+if((${CMAKE_SYSTEM_NAME} STREQUAL "Linux") OR
+   (${CMAKE_SYSTEM_NAME} STREQUAL "Darwin"))
   find_package(gz-transport13 QUIET REQUIRED OPTIONAL_COMPONENTS log)
   set(GZ_TRANSPORT_VER ${gz-transport13_VERSION_MAJOR})
 

src/plugins/point_cloud/PointCloud.cc

@@ -375,6 +375,11 @@ void PointCloudPrivate::PublishMarkers()
   marker.set_type(gz::msgs::Marker::POINTS);
   marker.set_visibility(gz::msgs::Marker::GUI);
 
+  // Set a default material - this will disable shadow casting when
+  // the material is processed by the MarkerManager.
+  gz::msgs::Material material;
+  marker.mutable_material()->CopyFrom(material);
+
   gz::msgs::Set(marker.mutable_scale(),
     gz::math::Vector3d::One * this->pointSize);