About the grass map

Development World Creation
1

Hi, I’d like to know what exactly is this grass map that builds when using the grass tool:

  1. Is the grass map size landscape dependent or field of view dependent? Useful to know how it scales with landscape size.
  2. What type of information does the grass map contain? I guess this is the placement pattern of each mesh…
  3. Can we modify the Grass Types and rebuild the grass map at runtime? If so is this a blocking operation?
  4. Where is the grass map stored?
  5. What is the grass map average size?
  6. Anything else useful to know on the grass map is welcome!
2

I’d love to learn some more about landscape grass as well.

  1. I suspect that the memory usage is landscape resolution dependent and that field of view effects the basepass/transluceny/dynamic shadow costs.

  2. I know the answer to his one! You can easily do this via a console command or via a blueprint executing a console command, Only problem I’ve found is that it makes any grass in the vicinity of the player dissapear and reappear. I do not believe it is a blocking operation as there was not much noticeable frame drop on my end. I suppose this probably means its in a different thread or handled asynchronously. (I’m not massive on the technical side of things so those are my best guesses.

The console command is is something like “dump grass” or “flush grass”, it’s easy to find!

3

Thanks @CupMcCakers, about 1. I would rather think the grass map is not landscape dependent but only dependent only on the grass density. The point is to present “fake” foliage items around the player, it is not to setup precise placement on the landscape as with regular foliage. I think there is no reason for the grass map to scale with the landscape, at least this would be how I would have implemented it… but I would like a confirmation.

Experimenting with changing the grass density in the Grass Type, we can see building the grass map takes less time (and there are less steps) when using a low density rather than a higher one. Changing the culling distance has no effect on the building of the map.

4

Hmm, i don’t really know, and this is all conjecture, but my assumption is that the Grass mesh will always be loaded in memory, then I suppose there will be a weighting map telling the “fake” grass instances which areas of the landscape to spawn on, which could be per vertex or be a texture. If that’s how it’s done, wouldn’t the memory cost would come down to the resolution of the landscape rather than the density of the instances?

Probably a random seed determines at generation the actual point, rotation and scale of each object.

The field of view then just determines which part of the grass map grass should be drawn on at any point?

The cost with additional density would not be memory based, but pure polygon crunching?