TODO:
 - Core thread gets stuck on shutdown when OpenGL is used...Somewhere in kernel

CONCRETE TASK:
 - SceneView editor window: Add a way to detect exact mouse position on the render texture
 - Extend SceneTreeView and ResourceTreeView that have events that occurr when selection changes
    - Events need to return SceneObject, Resource or Path (an array of any of those if needed)
 - Extend SceneTreeView and ResourceTreeView so that they have setSelection method accepting SceneObject/Resource-Path arrays
 - Similar to how I have onRenderViewport callback in Renderer have another one that gets triggered from core thread
   - Hook up gizmo rendering there
 - Hook up gizmo manager to ScenePicking so gizmos are considered when picking
   - I'll likely need to update GizmoManager so I can query gizmo SceneObject based on gizmo index

IMMEDIATE:
 - SceneGrid is very ugly. Consider using default lines for now and come back with a better approach later.
   - Potentially enable line AA?
 - Picking code is completely untested and will likely need major fixing
 - Disable DX9 for editor as I will likely want to use geometry shaders for icon rendering, and possibly new AA line shader
   - Or just use MeshHeap and update the icon/lines every frame?
 - Test all the new DrawHelper3D methods

 GIZMO TODO:
  - IMPORTANT: Gizmo rendering happens in update() but it should happen whenever scene view is being rendered as the render target isn't set anywhere
  - Figure out how to deal with builtin components like Camera and Renderable (e.g. how will they have gizmos since they're not managed components?)

LATER:
 - Need a way to render text for gizmos and handles, and in scene in general

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Handles

 - Make a few different base handle types:
   - Slider 1D (e.g. for movement using an arrow cap)
   - Slider 2D (e.g. for movement in 2D using a plane render)
   - Similar for scale/rotation handles  (see Unity for its implementations of those)

Handles should have colliders which will be queries whenever user input is detected in scene view
If any handle is hit the input will not proceed further (e.g. no picking will be done) and that handle control
will become active.

Base handle types should just be positioned in space and then return value every frame as user moves them.
 - This way they can also easily be used from C# for custom user-made stuff

TODO - Think about this
See for inspiration: http://docs.unity3d.com/ScriptReference/Handles.html

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SelectionRenderer

Retrieve a list of selected objects from SelectionManager
Find ones with Renderable components
Retrieve Meshes, and world transforms from them
Draw that same mesh with either a wireframe or a grayed out shader with a slight depth bias

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SceneView editor flow:
  Hook up gizmo, handle and selection rendering methods to be executed after the scene is rendered
  Calculate mouse coords manually relative to the window and to the render texture GUI element
     - Don't use GUI events as we require more precise control (do we?)

  Detect mouse clicks on the scene render target
      Forward those mouse coordinates to HandleManager
      It checks if screen ray intersects any handles and returns the handle if it does
         If handle is found it is activated and method returns
         Otherwise we mark the coordinates as selection start

  Detect mouse drag on the scene render target
    - If we have an active handle
         Forward mouse coordinates to the active handle so it can do its thing
         return
    - Otherwise its assumed we are dragging a selection
         Update selection endpoint and send it to ScenePicking
         Use Selection to select picked objects if any
         return

  Detect mouse release on scene render target
     If we have an active handle
        Clear active handle
        return
     Otheriwse its assumed we are dragging a selection
        Do nothing
        return