Grass is a performance problem before it’s anything else. A convincing meadow needs thousands upon thousands of blades, and VR is unforgiving — you’re rendering everything twice, once per eye, and a dropped frame is felt physically. So the grass system is built around two ideas that keep the cost down: draw it all at once, and only grow it where the player can see it.
Drawing it all at once
The expensive thing in rendering isn’t usually the number of triangles — it’s the number of separate draw calls. Every time you ask the graphics card to draw an object, there’s overhead. Ask it ten thousand times, once per grass blade, and the overhead alone sinks you.
The fix is instancing. The blade is a tiny mesh — a few triangles. Instead of drawing it ten thousand times, you hand the graphics card the blade once plus a list of ten thousand positions, and it draws all of them in a single call. Godot’s MultiMesh does exactly this. One blade design, one draw call, a whole tile’s worth of grass.
var mm := MultiMesh.new()
mm.mesh = blade_mesh
mm.instance_count = blades.size()
for i in range(blades.size()):
mm.set_instance_transform(i, blades[i]) # position, rotation, sizeEach blade gets a random position, rotation, height and a slightly varied colour, so the field doesn’t look like a regular grid.
Only near the player
Even with cheap drawing, covering an entire map in grass is wasteful — you can’t see most of it. So the grass exists only in a radius around the player, divided into tiles. As you walk, tiles ahead of you are built and tiles behind you are thrown away. The total amount of grass stays roughly constant no matter how big the world is, because it’s always just the patch around you.
To avoid a stutter when several tiles need building at once, only a few are built per frame, nearest first. You might occasionally notice grass filling in just ahead if you sprint, but the frame rate stays smooth, which matters far more in VR.
Less detail further out
Within that radius, not all grass needs to be equally fancy. The system uses rings: near tiles are dense and use a detailed curved blade; mid and far tiles get progressively sparser and use a simpler flat blade. You can’t tell the difference at distance, but the saving is large. When a tile crosses from one ring to another as you move, it’s rebuilt at the new detail level. This idea — more detail up close, less far away — is called level of detail, and it shows up all over the project.
Finally, the grass respects the world: it follows each biome’s grass density (lush in meadows, almost none in desert) and skips roads, water and building pads, using the same masks the earlier systems produced.
The grass also sways, which is the next post — wind, done entirely on the graphics card.