TileMesh does not support "empty" tiles

[MarkOates]

Components in Use

A somewhat disjointed problem among several components. The roles of each are not yet sorted out.

• AllegroFlare/Prototypes/Platforming2D/TMJDataLoader
• AllegroFlare/Prototypes/Platforming2D/TMJMeshLoader
• AllegroFlare/TileMaps/PrimMesh

Irregularities

• The magical tile 72 is used to replace 0 tiles when loading. 72 being a blank tile in one of the tileset bitmaps that was used at one point. This was probably done in a hackathon back in the day.
• Tiled, in the TMJ file, 0 is reserved for an empty tile, and the file will start tilesets at different indexes, starting with the first tileset at 1. AllegroFlare components are currently re-indexing all the tilesets to start at 0, and relying on a tileset's declaration at run time to include a single bitmap filename to be used as the tileset.
• As a temporary solution, some games (JourneyOfTheCat) will use automapping rules in Tiled to floodfill empty tiles with a blank tile in the tileset.
• In some components, tile indices are offset by 1.
• Should a negative value -1 indicate an empty tile? Are there locations where uint32_t is used as indices?
• Some TMJ data modifications are applied in AllegroFlare/Prototypes/Platforming2D/TMJDataLoader that should be moved to AllegroFlare/Prototypes/Platforming2D/TMJMeshLoader.

Desired features

• Ultimately, you should be able to use multiple tilesets within Tiled when designing the level, and AllegroFlare should composite and manage them together into a final tileset.
• In a TileMesh, vertices for empty tiles should be removed from the mesh (could be disabled through an optional flag). This technique has been done several times, in Hexagon's TextMesh, BitmapGridMesh, in AllegroFlare's MultiMesh, MusicMesh, etc. You might consider an indexed mesh, or, adding/removing tiles vertices entirely. Tiles may need to be sorted. You could even include background tiles in with the mesh.

Fastest possible would be a single mesh, holding all sprites and tiles, a single shader with different blending modes, additional shader data included in the vertex with correlated data in another bitmap like a normal map. Something like that.

[MarkOates]

This issue describes several different issues with the PrimMesh specifically. Since writing this issue, a new object TileMaps/TileMesh is created that permits empty tiles. It accomplishes this having an internal ALLEGRO_INDEX_BUFFER (along with a ALLEGRO_VERTEX_BUFFER). The tiles are "removed" by having the vertices removed from the index buffer via vertex_indices_for_tile_xy(x, y). They remain present in the vertex buffer.

This core issue is completed, however, the additional issues need to be broken down into separate issues.