Implement depth-first sorting algorithm for mapnodes

[SimplyLiz]

Currently the mapnodes are sorted by a Z-index. which works fairly well for 1x1 tiles.
For multitile buildings, it's not possible to calculate a Z-index that will work. Instead, mapNodes should be sorted by a depth search.

I think it's safe to assume, that only the BUILDINGS layer will inhabit multitile buildings. We will still need a basic Z-Order for the overlapping terrain tiles.
Worst case, we'll have two containers (with mapnode*) in two orders, and move the rendering to Map to render each layer.

I found this article:
http://shaunlebron.github.io/IsometricBlocks/
Source Code:
https://github.com/shaunlebron/IsometricBlocks

[iaGuoZhi]

Hi, I'd like to help with this issue. But I found that current implementation doesn't use Z-index. Is it ture? And why there will has multiple buildings in one node?

[SimplyLiz]

I'm refactoring mapNode soon to help with this as preparation. I'll tell you when i'm done and we can discuss the details.

But I found that current implementation doesn't use Z-index
This is true, nodes are ordered in "calculateVisibleNodes" in a for loop.