Terrain support?

[erichlof]

Hi @lo-th
First, thank you for putting in the effort to port this awesome physics engine! I will definitely be using this as my go-to physics engine for Three.js games.

I have some ideas for games that require terrain-shape support. I would like to put in a feature request to add a terrain class. Do you know this engine well enough to add it yourself, or, if not, do you think the original author would be able to add it?

I guess what would be needed is a simple 2-d array of vertex points that form a grid in the x-z plane. The number of width (x) and depth (z) would be supplied by the developer. Then, for each point a height value (y) is given by the developer. This is where my knowledge gets thin. I'm supposing a series of triangles would have to be made, storing a normal for each triangle. Then, somehow every triangle would have to be tested against all spheres and/or boxes in the scene (using the existing sphere-plane and box-plane routines?) Then the intersection point would have to be tested to be inside the triangle. Finally, an impulse is added to the sphere/box like it would be for a plane, or floor (which is already a part of this engine).

Please let me know what you are willing/able to do with this request. I could try to do one myself, but I don't see any point-in-triangle routines in the library as of yet.

Again, thanks for this wonderful project! :)
-Erich

[lo-th]

Thank's yes terrain this would be the top.
Saharan think of it for next release of OimoPhysics.
For the moment no triangle shape but is possible for sure.
I try to add this but if someone finds an idea I take

[erichlof]

Hi, that's great that Saharan wants to add it. I just might put an issue on his original repo and maybe I can help get the process started.

As for doing it on your own, there are numerous ray-triangle intersection tests out there (Three.js already has one in place). I'm pretty sure we could get a sphere to work, using the sphere's old center position as one end of a line segment and it's current position as the other end of the line segment. But the box is more difficult because of numerous edges and possible orientations. I don't really know how to do that.

A good place to look for ideas on terrain shape is here: https://github.com/bartdeboer/JigLibJS2/blob/master/geometry/JTerrain.js

and here for sphere-terrain collision code:
https://github.com/bartdeboer/JigLibJS2/blob/master/collision/CollDetectSphereTerrain.js

and box-terrain code:
https://github.com/bartdeboer/JigLibJS2/blob/master/collision/CollDetectBoxTerrain.js

EDIT: just found this triangle class: might be helpful
https://github.com/bartdeboer/JigLibJS2/blob/master/geometry/JTriangle.js

JigLibJS2 is also a good physics library, but unfortunately it is not in active development, both original and ports. There are some bugs in this engine I think but I don't know how to fix them.

Anyway, thanks for the info. I will contact Saharan and see what's happening with his terrain implementation. I have starred your repo and I look forward to what's coming next with Oimo!

Thanks!

[lo-th]

hum i think test sphere terrain for the moment
oimo can manage 1000 dynamique sphere i hop more when fixed

also add particule can be cool

[lo-th]

sphere terrain demo added :)

[erichlof]

@lo-th ,
Thank you so much for implementing this! It works great across all of my very different devices - old Windows XP desktop, 'newer' Windows 7 laptop, and even my Samsung Galaxy smartphone!

How did you end up implementing this? How does the internal terrain collision algorithm work? Are you using object (falling boxes' or balls')ray-triangle intersect test for each triangle of the terrain, or falling object's bounding sphere/ bounding box vs. terrain bounding sphere for each triangle of the terrain?

Regardless, this is a great addition to the already awesome Oimo engine - Thanks again! :)

[lo-th]

thank's, i use sphere collision, each vertex of terrain mesh have one sphere. box take many more calculation. is limited 64*64 sphere is good. Triangle can be the best option but i have to make some research about.

[ilixn]

@lo-th Hello, I've looked at your sphere terrain demo, but i didn't understand the concept...
Could you make a wiki page, or add some useful comments in tour code?
I've made the same thing, but without physics (here) and i would like to add physics to it.
Could you please help me (just give me a few explainations if you don't have much time😉) and give me a sort of "example code" ?
Excuse me, this issue is very old😃...
Thanks...