Multiple layers - render optimizations

I have an XML config file for my rendering which specifies multiple layers to 
render. When the program renders, I notice that it has to re-scan for chunks 
every time it starts a new layer. The render could save time by re-using the 
data from scanning once.

Also, for multiple layers with the same view direction and zoom levels (but 
different lighting for example), it might be faster to render all light levels 
on each tile at once.

Current psuedocode:
 render layer 1
  for each tile to update
   render tile

suggested psuedocode:
 for each tile to update in all layers where tiles overlap exactly
  render layers 1-n on tile

Original issue reported on code.google.com by masstroy21 on 30 Oct 2012 at 7:13

liuweireign / tectonicus

Multiple layers - render optimizations #19