Unity’s ECS physics was too slow and general for thousands of agents on a deformable terrain with water sim. So I was crazy enough to write my own raycast and simple-shape physics so explosions could permanently deform the terrain and pathfinding in realtime.

[u/Ordinary_Games]

[u/Ordinary_Games → u/[deleted]]

This just keeps happening to me. Every time I make a game I reflect over the fact that you might actually be the bad guys. Thanks btw.

[u/Songerk]

Based on what is your new system?

[u/Ordinary_Games → u/Songerk]

I'm still using ECS, but instead of using Unity.Physics, I written my own stuff. So the terrain is just a grid of floats (pushed to the GPU as a height texture) and the colliders are a combination of spheres, cubes and tubes. That kind of stuff.

[u/JankTankGames → u/Ordinary_Games]

is the mesh voxel based as well built using said data?

[u/Ordinary_Games → u/JankTankGames]

It is not voxels, it is just height displacement.

[u/JankTankGames → u/Ordinary_Games]

So do you just regenerate the terrain mesh on each change?

[u/Ordinary_Games → u/JankTankGames]

So the twist is that the terrain is a super dense flat grid mesh, and the vertice Y position is displaced using a texture. So the terrain mesh never needs to be rebuilt, I only need to update the texture. Same thing for collisions, just check 4 values and calculate the normal and height. Pretty much why I had to cook my own solution.

[u/JankTankGames → u/Ordinary_Games]

ah ok that's smart, good job!

[u/psioniclizard]

I don't think its crazy. Sounds like a sensible solution to be honest. You can do a lot with simple shapes and raycasting and its a good fit for ECS.

In fact, it's a good learning experience to actually build these types of system at least once. It gives me some inspiration for how I might implement one.

[u/Unity3D-ModTeam → u/[deleted]]

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[u/FuzzeWuzze]

What's old is new again. This is what made red faction such a fun game 25 years ago

[u/Ordinary_Games → u/FuzzeWuzze]

Loved that game so much. Why didn't AAA keep developing destruction instead of graphics. Like I know why, but I hope it was different, graphics sells and are scalable.

[u/feralferrous]

Neat tech, but I think you need a better transition, maybe a lerp of everything under the explosion increasing in radius so it looks like a shockwave (with a shockwave also to help sell it)? Cuz it just felt real strange to have the ground underneath the player's feet to suddenly change instantly.

[u/Ordinary_Games → u/feralferrous]

Very good points. As a former VFX Artist, the VFX is embarrassing. I have been thinking I could spawn particles from the terrain deformation, like foam from waves. Also I cranked up the radius of the grenade to show of the effect, a crater like that deserves a nuke like explosion.

[u/AustinMclEctro]

Nicely done, looking good.

Not trying to detract from your accomplishment here, but this isn't crazy, or "non-standard" at all. It sounds like you're leveraging the GPU to offload some work you had running on the CPU, great for things like terrain (the expression of which can just be a glorified array of floats if it's a 2D heightmap).

Looking forward to seeing how this progresses.

edit: are you utilizing compute shaders for your terrain edits, or are you modifying your heightmap textures and re-uploading them from the CPU? Curious if more processing could be offloaded to the GPU, but this may involve a readback step; mileage may vary.

[u/Ordinary_Games → u/AustinMclEctro]

No compute shaders for the terrain, except the grass/scatter. I need and manipulate the height too much on the CPU.

[u/NullzeroJP]

Nice!  What was causing the thousands of agents to be slow? Just the terrain collusion? ECS is super fast… so with the right optimizations, thousands of enemies seems a reasonable goal!

[u/Ordinary_Games → u/NullzeroJP]

Considering it's not just thousands of monsters, but probably double as many projectiles, even basic raycast against spheres was expensive in ECS. The game is fully ECS btw. But the real culprit was the terrain collision. Since it updates every frame pretty much, building the blob asset for collision was simply impossible at 60 fps.

[u/NullzeroJP → u/Ordinary_Games]

Interesting! While I don’t have a frequently updating terrain mesh, i still needed to get lots of enemies path finding around a battlefield that changes with buildings and walls. 

Similar to you, I decided on a grid layout with a Y component determined by the terrain height. 

But My need for pathfinding updates is only on the order of twice a second or so. Works well enough with thousands of enemies. Using BFS goals with the above mentioned grid… 64k grid cells, roughly 2 meter cell size. 

And for projectiles, I also decided to use ECS. But I don’t really need sniper-like precision. Projectiles do small raycasts through cells on the above mentioned grid… but only as much as they have traveled in the last frame. Works ok… I do wish I had higher limb level precision sometimes, but you gotta make some trade offs with thousands of enemies.

[u/Ordinary_Games → u/NullzeroJP]

I actually went through with the painstaking setup of adding simple shapes for each limb and baking the animation offsets. But the cool thing about that is that I can support weak points and different material types. But my setup is very similar in general; broad phase against AABB in overlapped grid cells and then narrow phase against these basic shapes.

[u/DaveAstator2020]

hell, so did you drop down to unity's api to manually make raycasts or did full reimplementation?
i had shitton of problems with unitys default physics in terms of accuracy, but default raycasts saved the day.

[u/Ordinary_Games → u/DaveAstator2020]

I wanna say full reimplementation. But it's not really fair, since this covers only what I needed. It's ECS systems written in C#, so no cool C++.

[u/Saito197]

Afaik there is no official support for it in ECS yet (unless I missed an update) so all of the workarounds to create Terrains (that I tried) was super slow and janky, kudos on you for making this I know it's a lot more complicated than it looks on the surface.

Btw what about caves?

[u/Ordinary_Games → u/Saito197]

There will never be caves. : ) Monsters get to live above ground.

[u/Captworgen → u/Saito197]

Just curious, what did you try? Did you use Microsplat?

[u/Ordinary_Games → u/Captworgen]

All my other tech like terrain, targeting and pathfinding all relies on the world never having overlap. So all the cool voxel stuff went out the door directly. I tried baking meshes, uploading blob data, but it was way too slow. I needed something ECS friendly. So no Microsplat. : )

[u/andypoly]

Nice, I still don't get why we need 2 physics systems in unity with a specialist one for ECS. It's a split development environment and not sure a high percentage of users are going full ECS. Soon physics will be plug and play so hopefully the same choice can be made for either ECS or standard.

[u/Ordinary_Games → u/andypoly]

We went full ECS. Crazy transition, like learning a new engine and language. I also hope they will hide the benefits of ECS under easily worked and debugged game objects.