Fixed volume calculation/Autoprice for 2d Polygonal regions

[CyphurTheFox]

Volume for a 2d polygonal region was not provided by WorldGuard, which breaks autoprice for these region types.

I implemented an algorithm for calculating the volume of a 2d poly region into the worldguard adapters. Should allow Autoprice to work for polygonal regions.

[alex9849]

Thanks for your contribution to AdvancedRegionMarket. Sadly your algorithm is incorrect.
The right region that you see in this picture contains exactly 24 blocks (and is ploygonal). The autoprice is set to 1$ per squareblock. Your algorithm somehow calculates that the region contains -14 (negative) blocks:
https://puu.sh/H9P6P/6e892722dc.jpg
I see you tried to implement the Shoelace formula. The problem with that approach is, that the area only gets calculated to the outer point (exclusively). What leads us to this problem:
https://puu.sh/H7Q4O/a2ca709e4c.png

Also, the Shoelace formula doesn't calculate the exact amount of blocks inside the region. You really get the area in the region (double), but we need the amount of blocks. For example a block that is located at the border of the region may be included into the region by WorldGuard, but the algorithm only counts it as a half block.

[CyphurTheFox]

Thanks for the feedback, I’ll take another crack at it with some different algorithms later. Hopefully I can put together something more satisfactory.