class TGLViewer: public TVirtualViewer3D, public TGLViewerBase

 Construct the viewer object, with following arguments:
    'pad' - external pad viewer is bound to
    'x', 'y' - initial top left position
    'width', 'height' - initial width/height

gl-embedded viewer's ctor
 Construct the viewer object, with following arguments:
    'pad' - external pad viewer is bound to
    'x', 'y' - initial top left position
    'width', 'height' - initial width/height

 Common initialization.

 Destroy viewer object.

 Indicate if viewer prefers to receive logical shape descriptions
 in local (kTRUE) or world frame (kFALSE). For GL viewer is kTRUE always
 TVirtualViewer3D interface overload - see base/src/TVirtualViewer3D.cxx
 for description of viewer architecture

 Scale and rotate a histo object to mimic placement in canvas.

 Iterate over pad-primitves and import them.

 Entry point for updating viewer contents via VirtualViewer3D
 interface.

 Start building of viewer scene.
 TVirtualViewer3D interface overload - see base/src/TVirtualViewer3D.cxx
 for description of viewer architecture.

 End building of viewer scene
 TVirtualViewer3D interface overload - see base/src/TVirtualViewer3D.cxx
 for description of viewer architecture

 Add an object to the viewer, using internal physical IDs
 TVirtualViewer3D interface overload - see base/src/TVirtualViewer3D.cxx
 for description of viewer architecture

 Add an object to the viewer, using an external physical ID
 TVirtualViewer3D interface overload - see base/src/TVirtualViewer3D.cxx
 for description of viewer architecture

 Open new composite container.
 TVirtualViewer3D interface overload - see base/src/TVirtualViewer3D.cxx
 for description of viewer architecture.

 Close composite container
 TVirtualViewer3D interface overload - see base/src/TVirtualViewer3D.cxx
 for description of viewer architecture

 Add composite operation used to combine objects added via AddObject
 TVirtualViewer3D interface overload - see base/src/TVirtualViewer3D.cxx
 for description of viewer architecture

 If we accepted all offered physicals into the scene no point in
 rebuilding it.

 Validate if the passed 'buffer' contains all sections we require to add object.
 Returns Int_t combination of TBuffer::ESection flags still required - or
 TBuffer3D::kNone if buffer is valid.
 If 'includeRaw' is kTRUE check for kRaw/kRawSizes - skip otherwise.
 See base/src/TVirtualViewer3D.cxx for description of viewer architecture

 Create and return a new TGLLogicalShape from the supplied buffer

 Create and return a new TGLPhysicalShape with id 'ID', using
 'buffer' placement information (translation etc), and bound to
 suppled 'logical'

 Build and return composite shape mesh

 Force a scene update.
 Code segments taken from protected RebuildScene().

 Resets position/rotation of current camera to default values.

 Setup cameras for current bounding box.

 Perform post scene (re)build setup

 Initialise GL state if not already done

 Post request for redraw of viewer at level of detail 'LOD'
 Request is directed via cross thread gVirtualGL object.

 Draw out the the current viewer/scene

 Draw reference marker and coordinate axes.

 Draw camera markup overlay.

 If in debug mode draw camera aids and overall bounding box.

 Perform GL work which must be done before each draw of scene

 Perform GL work which must be done after each draw of scene

 Make GL context current

 Swap GL buffers

 Post request for select draw of viewer, picking objects round the WINDOW
 point (x,y).
 Request is directed via cross thread gVirtualGL object

 Perform GL selection, picking objects overlapping WINDOW
 area described by 'rect'. Return kTRUE if selection should be
 changed, kFALSE otherwise.
 Select lock should already been taken in other thread in
 TGLViewer::ReqSelect().

 Process result from last selection (in fSelRec) and
 extract a new current selection from it.
 Here we only use physical shape.

 Post request for select draw of viewer, picking objects round the WINDOW
 point (x,y).
 Request is directed via cross thread gVirtualGL object

 Perform GL selection, picking overlay objects only.
 Return TRUE if the selected overlay-element has changed.

 Set viewer viewport (window area) with bottom/left at (x,y), with
 dimensions 'width'/'height'

 Set current active camera - 'cameraType' one of:
 kCameraPerspX, kCameraPerspY, kCameraPerspZ
 kCameraOrthoXOY, kCameraOrthoXOZ, kCameraOrthoZOY

 Set an orthographic camera to supplied configuration - note this
 does not need to be the current camera - though you will not see
 the effect if it is not.

 'camera' defines the ortho camera - one of kCameraOrthoXOY / XOZ / ZOY
 'left' / 'right' / 'top' / 'bottom' define the WORLD coordinates which
 corresepond with the left/right/top/bottom positions on the GL viewer viewport
 E.g. for kCameraOrthoXOY camera left/right are X world coords,
 top/bottom are Y world coords
 As this is an orthographic camera the other axis (in eye direction) is
 no relevant. The near/far clip planes are set automatically based in scene
 contents

 Set a perspective camera to supplied configuration - note this
 does not need to be the current camera - though you will not see
 the effect if it is not.

 'camera' defines the persp camera - one of kCameraPerspXOZ, kCameraPerspYOZ, kCameraPerspXOY
 'fov' - field of view (lens angle) in degrees (clamped to 0.1 - 170.0)
 'dolly' - distance from 'center'
 'center' - world position from which dolly/hRotate/vRotate are measured
             camera rotates round this, always facing in (in center of viewport)
 'hRotate' - horizontal rotation from initial configuration in degrees
 'hRotate' - vertical rotation from initial configuration in degrees

 Fetch the state of guides (axes & reference markers) into arguments

 Set the state of guides (axes & reference markers) from arguments

 Return selected physical shape.

 Emit signal indicating selection has changed

 Calcaulate and return pixel distance to nearest viewer object from
 window location px, py
 This is provided for use when embedding GL viewer into pad

 Process event of type 'event' - one of EEventType types,
 occuring at window location px, py
 This is provided for use when embedding GL viewer into pad

 Handle generic Event_t type 'event' - provided to catch focus changes
 and terminate any interaction in viewer

 Handle mouse button 'event'

 Handle mouse double click 'event'

 Handle configure notify 'event' - a window resize/movement

 Handle keyboard 'event'

 Handle mouse motion 'event'

 Handle window expose 'event' - show

 Handle window expose 'event' - show

 Pass viewer for print capture by TGLOutput.

 From VV3D:

 External GUI component interface