How do I represent blended tiles in a mesh/vertex array?

Question

I recently started making a Terraria clone using the LÖVE library, which is based in OpenGL.

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In Terraria, for each tile, there is a large texture with all possible combinations for merging with neighbouring tiles. They usually only support tiles of the same type, and sometimes other materials, like dirt. As a result, they only need a single vertex array.

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In Starbound, it seems to be simpler. A tutorial I found notes the use of basic 8x8 blocks, with a few edges drawn if the block is next to a block of a different type.

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I want to implement a similar mechanic, but I encountered a serious issue. A single vertex array does not allow z-ordering, which I would need.

• My first idea was to use one vertex array for each type of block, but that would eat a lot of memory.

• My second idea was to use the fact that OpenGL vertex array draws primitives in order. I could use some complicated data structure to represent tiles, so I would always know where to place their vertices in the array. However, that would either require moving lots of vertices or lots of memory.

What is the best way to implement this?

Answer 1

I found a way myself.

The key is to have two vertex arrays. In first you store solid blocks. In second you store edges, only if they are visible. Then you simply draw solid blocks first, then edges.

It is easy to add third array to store in-corners.

Vertex arrays look like these (from left: first, second, third array, final result)

Hope this helps somebody!