Port Ambient Occlusion plugin from gazebo-classic

[iche033]

Desired behavior

Port the Ambient Occlusion plugin from gazebo-classic to gz-rendering and offer an API to create ambient occlusion for a scene

Alternatives considered

Implement a new ambient occlusion method directly in gz-rendering

Implementation suggestion

Start off by porting the ambient occlusion plugin from gazebo-classic to ogre (ogre 1.x implementation in gz-rendering):
Source code:

• AmbientOcclusionVisualPlugin.cc
• AmbientOcclusionVisualPlugin.hh

Media files:

• CreaseShading.material
• CreaseShading.compositor
• Modulate.material
• GBuffer.material
• SSAOPost.material
• SSAOPost.compositor
• StdQuad_vp.program
• CreaseShadingFP.glsl
• GBufferFP.glsl
• ModulateFP.glsl
• NoFilterFP.glsl
• StdQuad_vp.glsl

This will help fleshout the API in Scene. As of gz-rendering8 there are currently a couple of functions to create global illumination (GI) in scene, namely CreateGlobalIlluminationVct, and CreateGlobalIlluminationCiVct. Since ambient occlusion can be treated as an approximation of GI, we could consider having a generic API that takes a GI type like:

 GlobalIlluminationPtr Scene::CreateGlobalIllumination(unsigned int _id, const std::string &_name, GlobalIlluminationType _type)

After the implementation is ported to ogre, the code and shaders will need to be ported to ogre2.

Additional context

Original pull request with screenshots: https://osrf-migration.github.io/gazebo-gh-pages/#!/osrf/gazebo/pull-requests/2916/page/1