class TGLScene: public TGLSceneBase

 Destroy scene objects

 Release all GL resources for current context identity.
 Requires iteration over all logical shapes.

 Fill scene-info with information needed for rendering, take into
 account the render-context (viewer state, camera, clipping).
 Here we have to iterate over all the physical shapes and select
 the visible ones. While at it, opaque and transparent shapes are
 divided into two groups.

 Setup LOD-dependant values in scene-info.
 We have to perform LOD quantization for all draw-elements.

 Initialize rendering.
 Pass to base-class where most work is done.
 Check if GL-ctx is shared with the previous one; if not
 wipe display-lists of all logicals.

 Render scene.

 Called after the rendering is finished.
 In debug mode draw statistcs is dumped.
 Parent's PostRender is called for GL cleanup.

 Do full rendering of scene.

 First draw the opaques, then the transparents. For each we do
 the number of passes required by draw mode and clipping setup.

 Render all opaque and transparent elements in the scene.

 Render DrawElements in elementVec with given timeout.
 If clipPlanes is non-zero, test each element against its
 clipping planes.

 Process selection record rec.
 'curIdx' is the item position where the scene should start
 its processing.
 Return TRUE if an object has been identified or FALSE otherwise.
 The scene-info member of the record is already set by the caller.

 Encapsulates all physical shapes bounding box with axes aligned box.
 Validity checked in the base-class.

 Adopt dynamically created logical 'shape' - add to internal map
 and take responsibility for deleting.

 Destroy logical shape defined by unique 'ID'.
 Returns kTRUE if found/destroyed - kFALSE otherwise.

 Destroy all logical shapes in scene.
 Return number of destroyed logicals.

 Find and return logical shape identified by unqiue logid.
 Returns 0 if not found.

 Adopt dynamically created physical 'shape' - add to internal map and take
 responsibility for deleting

 Virtual function to destroy a physical. Sub-classes might have
 special checks to perform.
 Caller should also invalidate the draw-list.

 Destroy physical shape defined by unique 'ID'.
 Returns kTRUE if found/destroyed - kFALSE otherwise.

 Destroy physical shapes that are no longer of interest to camera.
 If 'incModified' is true also the modified ones are deleted.
 Return count of number destroyed.

 Find and return physical shape identified by unqiue 'ID'.
 Returns 0 if not found.

 Returns the maximum used physical id.
 Returns 0 if empty.

 Put scene in update mode.

 Exit scene update mode, eventually notify scene consumers.

 Drop display-lists for the logical (assume TGLObject/direct rendering).
 Re-calculate the bounding box (also for all physicals).

 Reposition/recolor physical shape.

 Reposition/recolor physical shape.

 Reposition/recolor physical for given logical (assume TGLObject and
 a single physical).

 Reposition/recolor physical for given logical (assume TGLObject and
 a single physical).

 Moves logicals to refresh-cache.

 Wipes logicals in refresh-cache.

 Find and return logical shape identified by unqiue 'ID' in refresh-cache.
 Returns 0 if not found.

 Sort the TGLPhysical draw list by shape bounding box volume, from
 large to small. This makes dropout of shapes with time limited
 Draw() calls must less noticable. As this does not use projected
 size it only needs to be done after a scene content change - not
 everytime scene drawn (potential camera/projection change).

 Compare 'shape1' and 'shape2' bounding box volumes - return kTRUE if
 'shape1' bigger than 'shape2'.

 Return memory cost of scene.
 Warning: NOT CORRECT at present - doesn't correctly calculate size.
 of logical shapes with dynamic internal contents.

 Print sizes of logical nad physical-shape maps.

 Fill rgba color from ROOT color-index ci and transparency (0->100).

 Check if box is outside of all planes.